JP2010056137A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device for modulating carrier density and electric field in a carrier mobility direction, in a two-dimensional carrier gas channel generated in a compound semiconductor function layer. <P>SOLUTION: The semiconductor device (HEMT) 1 includes: a first compound semiconductor layer 21, having a two-dimensional carrier gas channel 23; a second compound semiconductor layer 22, disposed on the first compound semiconductor layer 21 and working as a barrier layer; a first main electrode 3 connected to one end of the two-dimensional carrier gas channel 23; and a second main electrode 4, connected to the other end separated from the one end of the two-dimensional carrier gas channel 23. In the semiconductor device, between the first main electrode 3 and the second main electrode 4, the composition ratio of a composition element of the second compound semiconductor layer 22 is different in the direction of the two-dimensional carrier gas channel 23. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a compound semiconductor functional layer.

  As an electronic device using a gallium nitride (GaN) -based compound semiconductor, a high electron mobility transistor (HEMT) is known. HEMT has high electron (carrier) mobility and is excellent in high-frequency characteristics.

  The HEMT is configured as a nitride-based semiconductor functional layer having a GaN layer functioning as a channel layer and an aluminum gallium nitride (AlGaN) layer functioning as a barrier layer stacked on the GaN layer by a heterojunction. Near the heterojunction of the GaN layer, a two-dimensional electron gas (2DEG) channel in which high mobility electrons travel is generated. A source electrode and a drain electrode are connected to the two-dimensional electron gas channel, and a gate electrode is disposed between the source electrode and the drain electrode. In the HEMT having such a structure, a high carrier density can be realized by a piezoelectric field using spontaneous polarization or lattice mismatch.

The HEMT is described in, for example, Patent Document 1 below.
WO 061038390

  However, in the above-described HEMT, the composition ratio of the composition element between the source electrode and the drain electrode of the barrier layer is constant, and by changing this composition ratio, a high carrier density or electric field in the two-dimensional electron gas channel is obtained. No consideration has been given to modulating the channel direction in the channel direction, that is, the carrier traveling direction.

  The present invention has been made to solve the above problems. Therefore, the present invention can modulate the carrier density and the electric field in the carrier traveling direction in the two-dimensional carrier gas channel generated in the compound semiconductor functional layer by changing the composition ratio of the composition element between the main electrodes of the barrier layer. It is to provide a semiconductor device that can be used.

  In order to solve the above-described problem, a first feature according to an embodiment of the present invention is that a semiconductor device includes a first compound semiconductor layer having a two-dimensional carrier gas channel, and a first compound semiconductor layer disposed on the first compound semiconductor layer. A second compound semiconductor layer that functions as a barrier layer, a first main electrode electrically connected to one end of the two-dimensional carrier gas channel, and the other end spaced from one end of the two-dimensional carrier gas channel A second main electrode that is electrically connected, and the composition ratio of the composition element of the second compound semiconductor layer is between the first main electrode and the second main electrode in the two-dimensional carrier gas channel direction. Is different.

  In the semiconductor device according to the first feature, the first compound semiconductor layer and the second compound semiconductor layer are both compound semiconductor layers containing nitrogen, and the two-dimensional carrier gas channel is a two-dimensional electron gas channel. preferable.

  In the semiconductor device according to the first feature, the composition ratio of the composition elements of the second compound semiconductor layer is preferably continuously different in the two-dimensional carrier gas channel direction.

  Further, in the semiconductor device according to the first feature, it is preferable that the composition ratio of the composition elements of the second compound semiconductor layer is gradually changed in the two-dimensional carrier gas channel direction.

  A second feature according to the embodiment of the present invention is that, in the semiconductor device, the first compound semiconductor layer having a two-dimensional carrier gas channel and the first compound semiconductor layer are disposed and function as a barrier layer. A second compound semiconductor layer; a source electrode electrically connected to one end of the two-dimensional carrier gas channel; a drain electrode electrically connected to the other end spaced from one end of the two-dimensional carrier gas channel; A gate electrode disposed between the source electrode and the drain electrode on the three-dimensional carrier gas channel, wherein the composition ratio of the composition element between the source electrode and the gate electrode of the second compound semiconductor layer is the second It is that it is large with respect to the composition ratio of the composition element between the drain electrode and gate electrode of a compound semiconductor layer.

  According to a third feature of the present invention, in the semiconductor device, the first compound semiconductor layer having a two-dimensional carrier gas channel and the first compound semiconductor layer are disposed and function as a barrier layer. A second compound semiconductor layer; a source electrode electrically connected to one end of the two-dimensional carrier gas channel; a drain electrode electrically connected to the other end spaced from one end of the two-dimensional carrier gas channel; A gate electrode disposed between the source electrode and the drain electrode on the three-dimensional carrier gas channel, wherein the composition ratio of the composition element between the drain electrode and the gate electrode of the second compound semiconductor layer is the second It is large with respect to the composition ratio of the composition element between the source electrode and the gate electrode of the compound semiconductor layer.

  According to a fourth aspect of the present invention, in the semiconductor device, the first compound semiconductor layer having a two-dimensional carrier gas channel and the first compound semiconductor layer are disposed on the first compound semiconductor layer and function as a barrier layer. A second compound semiconductor layer; an anode electrode electrically connected to one end of the two-dimensional carrier gas channel; and a cathode electrode electrically connected to the other end spaced apart from one end of the two-dimensional carrier gas channel. The composition ratio of the composition element on the anode electrode side between the anode electrode and the cathode electrode of the second compound semiconductor layer is larger than the composition ratio of the composition element on the cathode electrode side.

  According to a fifth feature of the present invention, in the semiconductor device, the first compound semiconductor layer having a two-dimensional carrier gas channel and the first compound semiconductor layer disposed on the first compound semiconductor layer function as a barrier layer. A second compound semiconductor layer; an anode electrode electrically connected to one end of the two-dimensional carrier gas channel; and a cathode electrode electrically connected to the other end spaced apart from one end of the two-dimensional carrier gas channel. The composition ratio of the composition element on the cathode electrode side is larger than the composition ratio of the composition element on the anode electrode side between the anode electrode and the cathode electrode of the second compound semiconductor layer.

  According to the present invention, the carrier density and electric field of the two-dimensional carrier gas channel generated in the compound semiconductor functional layer can be modulated in the carrier traveling direction by changing the composition ratio of the composition element between the main electrodes of the barrier layer. A semiconductor device that can be provided can be provided.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic and different from actual ones. In addition, there may be a case where the dimensional relationships and ratios are different between the drawings.

  Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is to arrange the components and the like as follows. Not specific. The technical idea of the present invention can be variously modified within the scope of the claims.

(First embodiment)
The first embodiment of the present invention describes an example in which the present invention is applied to a HEMT that is a three-terminal element as a semiconductor device, the generation of current collapse of this HEMT is reduced, and the breakdown voltage is improved. is there.

[Configuration of HEMT]
As shown in FIG. 1, a HEMT (semiconductor device) 1 according to the first embodiment includes a first compound semiconductor layer 21 having a two-dimensional carrier gas channel (channel region) 23, and a first compound semiconductor layer. A second compound semiconductor layer 22 functioning as a carrier generation region (barrier region) disposed on the heterojunction on 21, a first main electrode 3 connected to one end of a two-dimensional carrier gas channel 23, A second main semiconductor electrode 4 connected to the other end of the two-dimensional carrier gas channel 23, and a second compound semiconductor layer between the first main electrode 3 and the second main electrode 4. The composition ratio of the 22 composition elements differs in the direction of the two-dimensional carrier gas channel 23.

  The first compound semiconductor layer 21 and the second compound semiconductor layer 22 constitute the compound semiconductor functional layer 2, and the HEMT 1 is configured in the compound semiconductor functional layer 2. In the first embodiment, the compound semiconductor functional layer 2 is not shown, but directly on a substrate such as a silicon substrate, a silicon carbide substrate, or a sapphire substrate or for crystallinity matching of the compound semiconductor functional layer 2. It is indirectly formed through the buffer layer. The second compound semiconductor layer 22 of the compound semiconductor functional layer 2 has a smaller lattice constant and a larger band cap than the first compound semiconductor layer 21. Therefore, the second compound semiconductor layer 22 lattice-matched to the first compound semiconductor layer 21 receives a tensile stress.

Here, the compound semiconductor functional layer 2 is made of a group III nitride semiconductor material. A typical group III nitride semiconductor is represented by Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1).

Further, in the first embodiment, the Al (aluminum) composition ratio x1 of the first compound semiconductor layer 21 of the compound semiconductor functional layer 2 is in the range of 0 <x1 <1, and the second compound semiconductor layer 22 When the Al composition ratio x2 is in the range of 0 ≦ x2 <1, and the Al composition ratio x2 is larger than the Al composition ratio x1 (x1 <x2), the first compound semiconductor layer 21 is The second compound semiconductor layer 22 is composed of a nitride semiconductor material represented by Al _x2 Ga _1-x2 N. The nitride semiconductor material is represented by Al _x1 Ga _1-x1 N. That is, the compound semiconductor functional layer 2 includes a stacked structure of the first compound semiconductor layer 21 made of AlGaN and the second compound semiconductor layer 22 made of AlGaN, or made of the first compound semiconductor layer 21 made of GaN and AlGaN. It is constituted by a laminated structure with the second compound semiconductor layer 22.

  In the first embodiment, the film thickness of the first compound semiconductor layer 21 is set to 0.5 μm to 10.0 μm, for example, and here, in the case of a GaN layer, the film thickness is set to 0.5 μm to 3.5 μm, for example. Is set. The film thickness of the second compound semiconductor layer 22 is set to, for example, 10 nm-30 nm.

  In the compound semiconductor functional layer 2, the first compound semiconductor layer 21 is in the vicinity of the heterojunction interface between the first compound semiconductor layer 21 and the second compound semiconductor layer 22 and on the surface portion of the first compound semiconductor layer 21. Then, a two-dimensional carrier gas channel 23 (two-dimensional electron gas layer or two-dimensional hole gas layer) based on the spontaneous polarization and piezo polarization of the second compound semiconductor layer 22 is generated. Here, the two-dimensional carrier gas channel 23 functions as a channel region of electrons (carriers) having high mobility in the HEMT 1.

  In the first embodiment, the first main electrode 3 functions as a source electrode, and the second main electrode 4 functions as a drain electrode. The first main electrode 3 and the second main electrode 4 are ohmic electrodes connected to the two-dimensional carrier gas channel 23 with a low resistance. When a potential higher than the potential applied to the first main electrode 3 is applied to the second main electrode 4 and the gate electrode 5 is turned on, a current flows from the second main electrode 4 to the first main electrode 3. (Electrons as carriers flow in reverse). In the first embodiment, the first main electrode 3 and the second main electrode 4 are stacked on a Ti (titanium) layer having a film thickness of, for example, 10 nm to 50 nm and, for example, 100 nm to 1000 nm. It is comprised by the laminated film with Al layer which has the film thickness.

  The gate electrode 5 is disposed on the second compound semiconductor layer 22 and connected to the two-dimensional carrier gas channel 23 by a Schottky junction. The gate electrode 5 is a laminated film of a Ni (nickel) layer having a thickness of, for example, 100 nm to 500 nm and an Au (gold) layer having a thickness of, for example, 0.1 μm to 1.0 μm laminated on the Ni layer. It is comprised by.

  Although not clearly shown in FIG. 1 and the subsequent drawings, the dimension between the first main electrode 3 and the gate electrode 5 is between the second main electrode 4 and the gate electrode 5 because of the breakdown voltage. It is set shorter than the dimension.

  In the HEMT 1 configured as described above, as shown in FIG. 2, it is a composition element that affects the electric field strength E generated by spontaneous polarization and piezoelectric polarization of the second compound semiconductor layer 22 of the compound semiconductor functional layer 2. The Al composition ratio x2 is set high on the first main electrode 3 side between the first main electrode 3 and the second main electrode 4, and the second main electrode from the first main electrode 3 side is set. It decreases continuously toward the 4th side and is set low on the second main electrode 4 side. That is, the Al composition ratio x2 is continuously different in the direction of the two-dimensional carrier gas channel 23.

  As the Al composition ratio x2 increases, the band gap of the second compound semiconductor layer 22 widens, carriers increase, piezo polarization increases (distortion increases), and the electric field strength E increases. Conversely, when the Al composition ratio x2 is decreased, the band gap of the second compound semiconductor layer 22 is narrowed, carriers are decreased, piezoelectric polarization is weakened (distortion is reduced), and the electric field strength E is weakened. If the Al composition ratio x2 exceeds 0.5, it is difficult to form the second compound semiconductor layer 22 that functions as a barrier layer. On the other hand, if the Al composition ratio x2 is less than 0.1, the on-resistance of the HEMT 1 is increased. Therefore, it is preferable to continuously change the Al composition ratio x2 within this range (x2 = 0.1-0.5).

[Operation principle of HEMT]
As shown in FIG. 2, in the HEMT 1 according to the first embodiment described above, the composition ratio x2 of Al, which is the composition element of the second compound semiconductor layer 22, is high on the first main electrode 3 side. It decreases continuously in the direction of the two-dimensional carrier gas channel 23 from the first main electrode 3 side toward the second main electrode 4 side, and is set low on the second main electrode 4 side. That is, the Al composition ratio x2 of the second compound semiconductor layer 22 is different between the first main electrode 3 side and the second main electrode 4 side, and is asymmetric. Therefore, in the HEMT 1, the strain of the second compound semiconductor layer 22, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization, and the carrier density of the two-dimensional carrier gas channel 23 are different. The carrier density of the two-dimensional carrier gas channel 23 on the second main electrode 4 side of the second compound semiconductor layer 22 is lower than the carrier density of the two-dimensional carrier gas channel 23 on the first main electrode 4 side.

  In addition, as shown in FIG. 2, the electric field strength E generated by spontaneous polarization and piezoelectric polarization is lower on the second main electrode 4 side of the second compound semiconductor layer 22 than on the first main electrode 4 side. That is, when the voltage is applied so that the potential of the second main electrode 4 is higher than the potential of the first main electrode 3 and the HEMT 1 is in the OFF state, conventionally, the electric field on the second main electrode 4 side is Although the strength is increased, in the HEMT 1 according to the first embodiment, the electric field strength E generated by the spontaneous polarization and the piezoelectric polarization can be controlled in a decreasing direction, and the electric field strength distribution can be made uniform. Therefore, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode (drain electrode) 4 can be reduced, so that the occurrence of current collapse can be suppressed.

  Further, in the HEMT 1, the electric field strength E generated at the second main electrode 4 side end of the gate electrode 5 can be reduced as compared with the electric field strength E generated at the first main electrode 3 side end. The breakdown voltage can be improved.

[Method for manufacturing HEMT]
Although the manufacturing method is not specifically described with reference to the drawings, the second compound semiconductor layer 22 of the above-described HEMT 1 is formed by using the MOCVD method. For example, in a MOCVD apparatus, a method of supplying a flow rate ratio of trimethylaluminum (TMA) in an inclined manner on a substrate (wafer) on which the first compound semiconductor layer 21 is formed, or a method of performing a control for inclining the substrate temperature is used. The second compound semiconductor layers 22 having different Al composition ratios can be formed. Here, the flow rate ratio or the substrate temperature of TMA is set high on the first main electrode 3 side and low on the second main electrode 4 side.

  The second compound semiconductor layer 22 can be formed by introducing Al so that the composition ratio x2 is different in the direction of the two-dimensional carrier gas channel 23 using a gray scale mask method or a mask receding method. For the introduction of Al, for example, an ion implantation method or a solid phase diffusion method can be used practically.

[Characteristics of the first embodiment]
As described above, in the HEMT 1 according to the first embodiment, the carrier density and electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode 4 can be reduced, and the generation of current collapse can be suppressed. Further, in the HEMT 1, since the electric field intensity E at the end of the gate electrode 5 can be lowered, the breakdown voltage can be improved.

[First Modification]
The HEMT 1 according to the first modification of the first embodiment describes an example in which the nitride semiconductor material of the compound semiconductor functional layer 2 is replaced.

  The compound semiconductor functional layer 2 of the HEMT 1 according to the first modification is a stacked structure of a first compound semiconductor layer 21 made of InGaN and a second compound semiconductor layer 22 made of AlInN, or a first compound made of GaN. It is constituted by a laminated structure of a semiconductor layer 21 and a second compound semiconductor layer 22 made of AlInN.

The composition ratio y1 of In (indium) of the first compound semiconductor layer 21 is in the range of 0 <y1 <1, and the first compound semiconductor layer 21 is a nitride semiconductor material represented by In _Y Ga _1-y1 N It is. The Al composition ratio x2 of the second compound semiconductor layer 22 is in the range of 0 ≦ x2 <1, the In composition ratio y2 is in the range of 0 <y2 <1, and the second compound semiconductor layer 22 is Al _x2. It is a nitride semiconductor material represented by In _1-y2 N.

  In the HEMT 1 according to the first modified example, the electric field strength generated by spontaneous polarization and piezoelectric polarization of the second compound semiconductor layer 22 of the compound semiconductor functional layer 2 is similar to the HEMT 1 according to the first embodiment described above. The first main electrode between the first main electrode 3 and the second main electrode 4 is at least one of the composition ratio x2 of Al that is a composition element affecting E and the composition ratio Y2 of In. 3 is set higher on the third side, continuously decreases from the first main electrode 3 side toward the second main electrode 4 side, and is set lower on the second main electrode 4 side. That is, the Al composition ratio x2 or the In composition ratio y2 is continuously different in the direction of the two-dimensional carrier gas channel 23.

  In the HEMT 1 according to the first modified example configured as described above, the same operational effects as the operational effects obtained by the HEMT 1 according to the first embodiment can be achieved.

[Second Modification]
The HEMT 1 according to the second modification of the first embodiment describes an example in which the nitride semiconductor material of the compound semiconductor functional layer 2 is replaced.

  The compound semiconductor functional layer 2 of the HEMT 1 according to the second modification has a stacked structure of a first compound semiconductor layer 21 made of InGaN and a second compound semiconductor layer 22 made of AlGaN.

The In composition ratio y1 of the first compound semiconductor layer 21 is in the range of 0 <y1 <1, and the first compound semiconductor layer 21 is a nitride semiconductor material represented by In _Y Ga _1-y1 N. The Al composition ratio x2 of the second compound semiconductor layer 22 is in the range of 0 <x2 <1, and the second compound semiconductor layer 22 is a nitride semiconductor material represented by Al _x2 Ga _1-y2 N.

  In the HEMT 1 according to the second modified example, the electric field strength generated by spontaneous polarization and piezoelectric polarization of the second compound semiconductor layer 22 of the compound semiconductor functional layer 2 is similar to the HEMT 1 according to the first embodiment described above. The composition ratio x2 of Al, which is a composition element affecting E, is set high on the first main electrode 3 side between the first main electrode 3 and the second main electrode 4, and the first main electrode 3 It decreases continuously from the electrode 3 side toward the second main electrode 4 side, and is set low on the second main electrode 4 side. That is, the Al composition ratio x2 is continuously different in the direction of the two-dimensional carrier gas channel 23.

  In the HEMT 1 according to the second modified example configured as described above, the same operational effects as the operational effects obtained by the HEMT 1 according to the first embodiment can be achieved.

(Second Embodiment)
In the second embodiment of the present invention, an example in which the present invention is applied to a HEMT as a semiconductor device and the carrier speed of the HEMT is increased will be described.

[Configuration of HEMT]
As shown in FIG. 3, the HEMT (semiconductor device) 1 according to the second embodiment has the same basic structure as the HEMT 1 according to the first embodiment, but the second compound semiconductor layer 22. The Al composition ratio x2 is set low on the first main electrode 3 side, the Al composition ratio x2 is continuously increased from the first main electrode 3 toward the second main electrode 4, and the second The Al composition ratio x2 is set high on the main electrode 4 side. That is, the HEMT 1 according to the second embodiment is opposite to the two-dimensional carrier gas channel 23 direction in which the Al composition ratio of the second compound semiconductor layer 22 of the HEMT 1 according to the first embodiment is different. The Al composition ratio of the second compound semiconductor layer 22 differs in the direction.

[Operation principle of HEMT]
As shown in FIG. 3, in the HEMT 1 according to the above-described second embodiment, the composition ratio x2 of Al, which is the composition element of the second compound semiconductor layer 22, is low on the first main electrode 3 side. It increases continuously in the direction of the two-dimensional carrier gas channel 23 from the first main electrode 3 side toward the second main electrode 4 side, and is set higher on the second main electrode 4 side. That is, the Al composition ratio x2 of the second compound semiconductor layer 22 is different between the first main electrode 3 side and the second main electrode 4 side, and is asymmetric. Therefore, in the HEMT 1, the strain of the second compound semiconductor layer 22, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization, and the carrier density of the two-dimensional carrier gas channel 23 are different. The carrier density of the two-dimensional carrier gas channel 23 on the second main electrode 4 side of the second compound semiconductor layer 22 is higher than the carrier density of the two-dimensional carrier gas channel 23 on the first main electrode 4 side.

  In addition, as shown in FIG. 3, the electric field strength E generated by spontaneous polarization and piezoelectric polarization is higher on the second main electrode 4 side of the second compound semiconductor layer 22 than on the first main electrode 3 side. That is, the electric field strength E can be increased (modulated) based on the spontaneous polarization and the piezo polarization in the direction opposite to the electric field direction from the second main electrode 4 toward the first main electrode 3 (carrier traveling direction). it can. Therefore, in the HEMT 1, the carriers in the two-dimensional carrier gas channel 23 in the vicinity of the second main electrode (drain electrode) 4 can be accelerated, so that the switching speed can be increased.

  In addition, since the manufacturing method of HEMT1 which concerns on 2nd Embodiment is the same as the manufacturing method of HEMT1 which concerns on the above-mentioned 1st Embodiment, description here is abbreviate | omitted, since it overlaps. In addition, the HEMT 1 according to the second embodiment is made of a material having a laminated structure of the compound semiconductor functional layer 2 in the same manner as the HEMT 1 according to the first modification and the second modification of the first embodiment. Can be changed.

[Characteristics of Second Embodiment]
As described above, in the HEMT 1 according to the second embodiment, the carrier density and the electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the HEMT 1, the electric field strength E in the vicinity of the second main electrode 4 can be increased, and the carriers in the two-dimensional carrier gas channel 23 can be accelerated, so that the switching speed can be increased. Can do.

(Third embodiment)
In the third embodiment of the present invention, an example in which the present invention is applied to a HEMT as a semiconductor device, the carrier speed of the HEMT is increased, and the breakdown voltage is improved will be described.

[Configuration of HEMT]
As shown in FIG. 4, the HEMT (semiconductor device) 1 according to the third embodiment has the same basic structure as the HEMT 1 according to the first embodiment, but the second compound semiconductor layer 22. The Al composition ratio x2 is set high on the first main electrode 3 side, the Al composition ratio x2 is continuously decreased from the first main electrode 3 toward the gate electrode 5, and the gate electrode 5 portion, particularly the first The Al composition ratio x2 is set low at the end of the main electrode 4 on the second side, the Al composition ratio x2 is continuously increased from the gate electrode 5 toward the second main electrode 4, and the second main electrode 4 On the side, the Al composition ratio x2 is set high again. That is, in the HEMT 1, the Al composition ratio x2 of the second compound semiconductor layer 22 is set low in the region corresponding to the gate electrode 5 and set high on the second main electrode 4 side.

[Operation principle of HEMT]
As shown in FIG. 4, in the HEMT 1 according to the third embodiment described above, the composition ratio x2 of Al, which is the composition element of the second compound semiconductor layer 22, is high on the first main electrode 3 side. 1 continuously decreases in the direction of the two-dimensional carrier gas channel 23 from the main electrode 3 side to the gate electrode 5 side, and is set low in a region corresponding to the gate electrode 5. The Al composition ratio x2 of the second compound semiconductor layer 22 continuously increases in the direction of the two-dimensional carrier gas channel 23 from the gate electrode 5 side toward the second main electrode 4 side. High on the 4th side. That is, the Al composition ratio x2 of the second compound semiconductor layer 22 is different between the first main electrode 3 side, the second main electrode 4 side, and the region corresponding to the gate electrode 5, and the gate electrode 5 is the center. The first main electrode 3 side and the second main electrode 4 side are almost symmetrical. Therefore, in the HEMT 1, the strain of the second compound semiconductor layer 22, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization, and the carrier density of the two-dimensional carrier gas channel 23 are different. On the second main electrode 4 side of the second compound semiconductor layer 22, the carrier density of the two-dimensional carrier gas channel 23 is higher than the carrier density of the two-dimensional carrier gas channel 23 in the region corresponding to the gate electrode 5.

  As shown in FIG. 4, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization is higher than the region corresponding to the gate electrode 5 on the second main electrode 4 side of the second compound semiconductor layer 22. That is, the electric field strength E can be increased (modulated) based on the spontaneous polarization and the piezo polarization in the direction opposite to the electric field direction from the second main electrode 4 toward the first main electrode 3 (carrier traveling direction). it can. Therefore, in the HEMT 1, the carriers in the two-dimensional carrier gas channel 23 in the vicinity of the second main electrode (drain electrode) 4 can be accelerated, so that the switching speed can be increased.

  In the HEMT 1, the electric field strength E generated at the second main electrode 4 side end of the gate electrode 5 can be reduced as compared with the electric field strength E generated at the second main electrode 4 side end. The breakdown voltage can be improved.

  In addition, since the manufacturing method of HEMT1 which concerns on 3rd Embodiment is the same as that of the manufacturing method of HEMT1 which concerns on the above-mentioned 1st Embodiment, since description here overlaps, it abbreviate | omits. Further, the HEMT 1 according to the third embodiment is made of a material having a laminated structure of the compound semiconductor functional layer 2 as in the HEMT 1 according to the first modification and the second modification of the first embodiment. Can be changed.

[Characteristics of Third Embodiment]
As described above, in the HEMT 1 according to the third embodiment, the carrier density and the electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode 4 can be reduced, and the generation of current collapse can be suppressed. Further, in the HEMT 1, since the electric field intensity E at the end of the gate electrode 5 can be lowered, the breakdown voltage can be improved.

(Fourth embodiment)
In the fourth embodiment of the present invention, an example in which the present invention is applied to a HEMT as a semiconductor device and the occurrence of current collapse in the HEMT is reduced will be described.

[Configuration of HEMT]
As shown in FIG. 5, the HEMT (semiconductor device) 1 according to the fourth embodiment has the same basic structure as the HEMT 1 according to the first embodiment, but the second compound semiconductor layer 22. The Al composition ratio x2 is set low on the first main electrode 3 side, the Al composition ratio x2 is continuously increased from the first main electrode 3 toward the gate electrode 5, and Al in the gate electrode 5 portion is increased. The composition ratio x2 is set high, the Al composition ratio x2 is continuously decreased from the gate electrode 5 toward the second main electrode 4, and the Al composition ratio x2 is lowered again on the second main electrode 4 side. It is set. That is, in the HEMT 1, the Al composition ratio x2 of the second compound semiconductor layer 22 is set high in the region corresponding to the gate electrode 5, and is set low on the second main electrode 4 side.

[Operation principle of HEMT]
As shown in FIG. 5, in the HEMT 1 according to the above-described fourth embodiment, the composition ratio x2 of Al, which is the composition element of the second compound semiconductor layer 22, is low on the first main electrode 3 side. 1 continuously increases in the direction of the two-dimensional carrier gas channel 23 from the main electrode 3 side toward the gate electrode 5 side, and is set high in a region corresponding to the gate electrode 5. The Al composition ratio x2 of the second compound semiconductor layer 22 continuously decreases in the direction of the two-dimensional carrier gas channel 23 from the gate electrode 5 side toward the second main electrode 4 side. It is set low on the 4th side. That is, the Al composition ratio x2 of the second compound semiconductor layer 22 is different between the first main electrode 3 side, the second main electrode 4 side, and the region corresponding to the gate electrode 5, and the gate electrode 5 is the center. The first main electrode 3 side and the second main electrode 4 side are almost symmetrical. Therefore, in the HEMT 1, the strain of the second compound semiconductor layer 22, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization, and the carrier density of the two-dimensional carrier gas channel 23 are different. On the second main electrode 4 side of the second compound semiconductor layer 22, the carrier density of the two-dimensional carrier gas channel 23 is lower than the carrier density of the two-dimensional carrier gas channel 23 in the region corresponding to the gate electrode 5.

  Further, as shown in FIG. 5, the electric field strength E generated by spontaneous polarization and piezoelectric polarization is lower than the region corresponding to the gate electrode 5 on the second main electrode 4 side of the second compound semiconductor layer 22. That is, when the voltage is applied so that the potential of the second main electrode 4 is higher than the potential of the first main electrode 3 and the HEMT 1 is in the OFF state, conventionally, the electric field on the second main electrode 4 side is Although the strength is increased, in the HEMT 1 according to the fourth embodiment, the electric field strength E generated by the spontaneous polarization and the piezoelectric polarization can be controlled in a decreasing direction, and the electric field strength distribution can be made uniform. Therefore, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode (drain electrode) 4 can be reduced, so that the occurrence of current collapse can be suppressed.

  In addition, since the manufacturing method of HEMT1 which concerns on 4th Embodiment is the same as the manufacturing method of HEMT1 which concerns on the above-mentioned 1st Embodiment, description here is abbreviate | omitted, since it overlaps. Further, the HEMT 1 according to the fourth embodiment is made of a material having a laminated structure of the compound semiconductor functional layer 2 as in the HEMT 1 according to the first and second modifications of the first embodiment. Can be changed.

[Features of Fourth Embodiment]
As described above, in the HEMT 1 according to the fourth embodiment, the carrier density and the electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode 4 can be reduced, and the generation of current collapse can be suppressed.

(Fifth embodiment)
The fifth embodiment of the present invention describes an example in which the present invention is applied to a HEMT as a semiconductor device, and the generation of current collapse of the HEMT is reduced.

[Configuration of HEMT]
As shown in FIG. 6, the HEMT (semiconductor device) 1 according to the fifth embodiment has the same basic structure as the HEMT 1 according to the first embodiment, but the second compound semiconductor layer 22 is the same. The Al composition ratio x2 is set high on the first main electrode 3 side, and the Al composition ratio x2 is gradually decreased from the first main electrode 3 toward the second main electrode 4, so that the second The Al composition ratio x2 is set low on the main electrode 4 side. That is, in the HEMT 1, the second compound semiconductor layer 22 includes a first region 22 A in which the Al composition ratio x 2 is set high on the first main electrode 3 side, and the Al composition ratio x 2 is low. The set third region 22C is disposed on the second main electrode 4 side, and the second region 22B set to the intermediate Al composition ratio x2 between the first region 22A and the third region It is arranged between 22C. Here, in a stepwise manner, a region with a constant Al composition ratio continues continuously at a predetermined distance in the direction of the two-dimensional carrier gas channel 23, and then another region with another constant Al composition ratio differs from that. It means that it continues continuously at a predetermined distance in the direction of the dimension carrier gas channel 23.

[Operation principle of HEMT]
As shown in FIG. 6, in the HEMT 1 according to the fifth embodiment described above, the composition ratio x2 of Al, which is the composition element of the second compound semiconductor layer 22, is high on the first main electrode 3 side. It decreases stepwise in the direction of the two-dimensional carrier gas channel 23 from the first main electrode 3 side toward the second main electrode 4 side, and is set lower on the second main electrode 4 side. That is, the Al composition ratio x2 of the second compound semiconductor layer 22 is different between the first main electrode 3 side and the second main electrode 4 side and is asymmetric. Therefore, in the HEMT 1, the strain of the second compound semiconductor layer 22, the electric field intensity E generated by spontaneous polarization and piezoelectric polarization, and the carrier density of the two-dimensional carrier gas channel 23 are different. On the second main electrode 4 side of the second compound semiconductor layer 22, the carrier density of the two-dimensional carrier gas channel 23 is lower than the carrier density of the two-dimensional carrier gas channel 23 in the region corresponding to the gate electrode 5.

  Further, as shown in FIG. 6, the electric field strength E generated by spontaneous polarization and piezoelectric polarization is larger than the region corresponding to the first main electrode 3 side on the second main electrode 4 side of the second compound semiconductor layer 22. Lower. That is, when the voltage is applied so that the potential of the second main electrode 4 is higher than the potential of the first main electrode 3 and the HEMT 1 is in the OFF state, conventionally, the electric field on the second main electrode 4 side is Although the strength is increased, in the HEMT 1 according to the fifth embodiment, the electric field strength E generated by the spontaneous polarization and the piezoelectric polarization can be controlled in a decreasing direction, and the electric field strength distribution can be made uniform. Therefore, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode (drain electrode) 4 can be reduced, so that the occurrence of current collapse can be suppressed.

[Method for manufacturing HEMT]
A method for manufacturing the HEMT 1 according to the fifth embodiment described above is as follows.

  First, as shown in FIG. 7, the first region 22A of the second compound semiconductor layer 22 is formed on the first compound semiconductor layer 21 at least in the region where the two-dimensional carrier gas channel 23 of the HEMT 1 is formed. The The first region 22A is a compound semiconductor layer having a high composition ratio of Al, which is a composition element. The first region 22A is formed by, for example, the MOCVD method, and the Al composition ratio is controlled by adjusting the flow ratio of TMA during the film formation.

  On the first region 22A, a mask 221 in which regions for forming the second region 22B and the third region 22C are opened is formed. For example, a silicon oxide film can be used for the mask 221. As shown in FIG. 8, the first region 22 </ b> A exposed from the opening is removed by etching using a mask 221. Subsequently, as shown in FIG. 9, the second region 22 </ b> B of the second compound semiconductor layer 22 is formed on the first compound semiconductor layer 21 using the mask 221. The second region 22B is a compound semiconductor layer having an intermediate composition ratio of Al as a composition element. Similarly to the first region 22A, the second region 22B is formed by, for example, the MOCVD method, and the Al composition ratio is controlled by adjusting the flow rate ratio of TMA during the film formation. Thereafter, the mask 221 is removed.

  On the first region 22A and the second region 22B, a mask 222 in which a region for forming the third region 22C is opened is formed. For example, a silicon oxide film can be used for the mask 222. As shown in FIG. 10, the second region 22 </ b> B exposed from the opening is removed by etching using a mask 222. Subsequently, as shown in FIG. 11, the third region 22 </ b> C of the second compound semiconductor layer 22 is formed on the first compound semiconductor layer 21 using the mask 222. The third region 22C is a compound semiconductor layer having a low composition ratio of Al, which is a composition element. Similarly to the first region 22A and the second region 22B, the third region 22C is formed by, for example, MOCVD, and the Al composition ratio is adjusted by adjusting the flow rate ratio of TMA at the time of this film formation. Control. When the third region 22C is formed, the second compound semiconductor layer 22 is completed. Thereafter, the mask 222 is removed.

  In addition, when each of the first region 22A and the second region 22B of the second compound semiconductor layer 22 is removed by etching, etching reaching the first compound semiconductor layer 21 may be performed. In this case, as described above, generation of crystal defects in the vicinity of the heterojunction interface can be prevented.

  The formation order of the first region 22A, the second region 22B, and the third region 22C of the second compound semiconductor layer 22 may be reversed, or the second region 22B, the first region The order of formation of the region 22A and the third region 22C, or the order of formation of the second region 22B, the third region 22C, and the first region 22A may be used.

Also,
[Features of Fifth Embodiment]
As described above, in the HEMT 1 according to the fifth embodiment, the carrier density and electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the HEMT 1, the generation of hot electrons in the vicinity of the second main electrode 4 can be reduced, and the generation of current collapse can be suppressed.

  Note that, in the HEMT 1 according to the fifth embodiment, the material of the stacked structure of the compound semiconductor functional layer 2 is used as in the HEMT 1 according to the first modification and the second modification of the first embodiment described above. Can be changed.

[Modification]
The HEMT 1 according to the modification of the fifth embodiment is the first main electrode of the second compound semiconductor layer 22 of the compound semiconductor functional layer 2 in the HEMT 1 according to the fifth embodiment shown in FIG. The Al composition ratio x2 of the first region 22A disposed on the third side is low, the Al composition ratio x2 of the third region 22C is high, and the Al composition ratio x2 of the second region 22B is intermediate between the two. Is set. That is, in the HEMT 1 according to the modification of the fifth embodiment, the Al composition ratio x2 is set low on the first main electrode 3 side of the second compound semiconductor layer 22, and The Al composition ratio x2 is increased stepwise toward the second main electrode 4, and the Al composition ratio x2 is set higher on the second main electrode 4 side.

  In the HEMT 1 according to the modification of the fifth embodiment configured as described above, the carrier density and the electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 are modulated in the carrier traveling direction. be able to. As a result, in the HEMT 1, the electric field strength E in the vicinity of the second main electrode 4 can be increased, and the carriers in the two-dimensional carrier gas channel 23 can be accelerated, so that the switching speed can be increased. Can do.

(Sixth embodiment)
In the sixth embodiment of the present invention, an example in which the present invention is applied to a Schottky barrier diode (SBD) that is a two-terminal element as a semiconductor device and the breakdown voltage of the SBD is improved will be described.

[Configuration of SBD]
As shown in FIG. 12, the SBD (semiconductor device) 11 according to the fourth embodiment includes a first compound semiconductor layer 21 having a two-dimensional carrier gas channel 23 and a heterogeneity on the first compound semiconductor layer 21. Connected to the second compound semiconductor layer 22 disposed by bonding, the first main electrode 3 connected to one end of the two-dimensional carrier gas channel 23, and the other end separated from one end of the two-dimensional carrier gas channel 23 The second main electrode 4 is provided, and the composition ratio of the composition element of the second compound semiconductor layer 22 between the first main electrode 3 and the second main electrode 4 is two-dimensional carrier gas channel 23. Different in direction. In the sixth embodiment, the first main electrode 3 is used as a cathode electrode that is ohmically connected to the two-dimensional carrier gas channel 23, and the second main electrode 4 is an anode that is Schottky connected to the two-dimensional carrier gas channel 23. Used as an electrode.

  Here, the compound semiconductor functional layer 2 is a nitride-based semiconductor functional layer, similar to the compound semiconductor functional layer 2 of the HEMT 1 according to the first embodiment described above. A composition ratio x2 of Al, which is a composition element on the first main electrode 3 (anode electrode) side, between the first main electrode 3 and the second main electrode 4 of the second compound semiconductor layer 22 is: It is set higher than the composition ratio x2 of Al, which is a composition element on the second main electrode (cathode electrode) 4 side.

  In the SBD 11, the electric field tends to concentrate on the second main electrode (cathode electrode) 4 side that becomes a Schottky connection. Therefore, similarly to the HEMT 1 according to the first embodiment described above, by setting the Al composition ratio x2 on the second main electrode 4 side of the second compound semiconductor layer 22 to be low, The carrier density in the vicinity of the second main electrode 4 of the dimensional carrier gas channel 23 can be reduced, and the electric field strength E can be reduced.

  The stacked structure of the compound semiconductor functional layer 2 of the SBD 11 according to the sixth embodiment is the same as the compound semiconductor functional layer of the HEMT 1 according to the first modification and the second modification of the first embodiment described above. You may change into the laminated structure of 2.

[Features of Sixth Embodiment]
As described above, in the SBD 11 according to the sixth embodiment, the carrier density and the electric field strength E of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 can be modulated in the carrier traveling direction. . As a result, in the SBD 11, since the electric field strength E in the vicinity of the second main electrode 4 can be weakened, the breakdown voltage can be improved.

[Modification]
The SBD 11 according to the modified example of the sixth embodiment shown in FIG. 13 has the same basic structure as the SBD 11 shown in FIG. 12, but the second compound semiconductor layer 22 on the first main electrode 3 side is the same. The Al composition ratio x2 is set low, and the Al composition ratio x2 on the second main electrode 4 side of the second compound semiconductor layer 22 is set high.

  In the SBD 11 according to the modified example configured as described above, as described in the HEMT 1 according to the second embodiment described above, the carrier density of the two-dimensional carrier gas channel 23 generated in the compound semiconductor functional layer 2 and The electric field strength E can be modulated in the carrier traveling direction. As a result, in the SBD 11, the electric field strength E in the vicinity of the second main electrode 4 can be increased, and the carriers in the two-dimensional carrier gas channel 23 can be accelerated, so that the switching speed can be increased. Can do.

  In the SBD 11 according to the sixth embodiment and its modification, the composition ratio of the composition elements of the second compound semiconductor layer 22 is continuously changed in the two-dimensional carrier gas channel 23 direction. Similarly to the HEMT 1 according to the fifth embodiment, the composition ratio of the composition elements of the second compound semiconductor layer 22 may be changed stepwise in the direction of the two-dimensional carrier gas channel 23.

(Other embodiments)
As described above, the present invention has been described by a plurality of embodiments. However, the description and the drawings constituting a part of this disclosure do not limit the present invention. The present invention can be applied to various alternative embodiments, examples, and operational technologies.

  For example, in the present invention, the bottom surface of at least one of the first main electrode 3, the second main electrode 4, and the gate electrode 5 may be engraved until it reaches the first compound semiconductor layer 21. In the present invention, the gate electrode 5 may also be engraved like a well-known recess gate structure.

  Further, in the present invention, the thickness of the second compound semiconductor layer 22 is increased from the end of the second main electrode 4 opposite to the first main electrode 3 toward the end of the second compound semiconductor layer 22. You may comprise so that it may increase.

  Furthermore, the present invention is not limited to a single layer structure or a multi-layer structure, and the Al composition ratio may be changed in the thickness direction of the second compound semiconductor layer 22. For example, in the second compound semiconductor layer 22, the Al composition ratio x2 on the first main electrode 3 side is set to a low region and a high region in the thickness direction, and the Al composition on the second main electrode 4 side is set. The ratio x2 may be set only in the low region.

  Furthermore, in the present invention, the composition ratio of the composition elements of the second compound semiconductor layer 22 may be changed stepwise in two or four steps in the direction of the two-dimensional carrier gas channel 23.

  Further, in the present invention, the second compound semiconductor layer 22 having a dopant may be stacked on the first compound semiconductor layer 21 via a non-doped (i-type) compound semiconductor layer. In the present invention, the second compound semiconductor layer 22 may be stacked on the first compound semiconductor layer 21 via a spacer layer. For example, an AlN layer can be used as the spacer layer.

  Furthermore, the present invention provides a cap layer that is composed of, for example, a GaN layer between the second compound semiconductor layer 22 and the first main electrode 3 and the second main electrode 4 to reduce the surface level of carriers. It may be arranged.

1 is a cross-sectional view of main parts of a semiconductor device according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating an electric field distribution state and a composition profile of a composition element of the semiconductor device illustrated in FIG. 1. It is typical sectional drawing explaining the electric field distribution state of the semiconductor device which concerns on the 2nd Embodiment of this invention, and the composition profile of a composition element. It is typical sectional drawing explaining the electric field distribution state of the semiconductor device which concerns on the 3rd Embodiment of this invention, and the composition profile of a composition element. It is typical sectional drawing explaining the electric field distribution state of the semiconductor device which concerns on the 4th Embodiment of this invention, and the composition profile of a composition element. It is typical sectional drawing explaining the electric field distribution state of the semiconductor device which concerns on the 5th Embodiment of this invention, and the composition profile of a composition element. It is 1st process sectional drawing explaining the manufacturing method of the semiconductor device which concerns on 5th Embodiment. It is 2nd process sectional drawing. It is 3rd process sectional drawing. It is a 4th process sectional view. FIG. 10 is a fifth process cross-sectional view. It is a typical sectional view explaining the electric field distribution state of a semiconductor device concerning a 6th embodiment of the present invention, and the composition profile of a composition element. It is a typical sectional view explaining the electric field distribution state of a semiconductor device concerning the modification of a 6th embodiment, and the composition profile of a composition element.

Explanation of symbols

1 ... Semiconductor device (HEMT)
2 ... Compound semiconductor functional layer 21 ... First compound semiconductor layer (carrier passage region)
22 ... Second compound semiconductor layer (carrier generation region)
22A ... 1st area | region 22B ... 2nd area | region 22C ... 3rd area | region 221, 222 ... Mask 23 ... Two-dimensional carrier gas channel 3 ... 1st main electrode (source electrode or anode electrode)
4 ... 2nd main electrode (drain electrode or cathode electrode)
5 ... Gate electrode 11 ... Semiconductor device (SBD)

Claims (8)

A first compound semiconductor layer having a two-dimensional carrier gas channel;
A second compound semiconductor layer disposed on the first compound semiconductor layer and functioning as a barrier layer;
A first main electrode connected to one end of the two-dimensional carrier gas channel;
A second main electrode connected to the other end spaced from one end of the two-dimensional carrier gas channel,
A semiconductor device characterized in that a composition ratio of composition elements of the second compound semiconductor layer differs in the two-dimensional carrier gas channel direction between the first main electrode and the second main electrode.   The first compound semiconductor layer and the second compound semiconductor layer are both compound semiconductor layers containing nitrogen, and the two-dimensional carrier gas channel is a two-dimensional electron gas channel. The semiconductor device described.   3. The semiconductor device according to claim 1, wherein a composition ratio of composition elements of the second compound semiconductor layer is continuously different in a direction of the two-dimensional carrier gas channel. 4.   3. The semiconductor device according to claim 1, wherein the composition ratio of the composition elements of the second compound semiconductor layer varies stepwise in the direction of the two-dimensional carrier gas channel. A first compound semiconductor layer having a two-dimensional carrier gas channel;
A second compound semiconductor layer disposed on the first compound semiconductor layer and functioning as a barrier layer;
A source electrode connected to one end of the two-dimensional carrier gas channel;
A drain electrode connected to the other end spaced from one end of the two-dimensional carrier gas channel;
A gate electrode disposed between the source electrode and the drain electrode on the two-dimensional carrier gas channel;
The composition ratio of the composition element between the source electrode and the gate electrode of the second compound semiconductor layer is the composition ratio of the composition element between the drain electrode and the gate electrode of the second compound semiconductor layer. A semiconductor device characterized by being larger than the above. A first compound semiconductor layer having a two-dimensional carrier gas channel;
A second compound semiconductor layer disposed on the first compound semiconductor layer and functioning as a barrier layer;
A source electrode connected to one end of the two-dimensional carrier gas channel;
A drain electrode connected to the other end spaced from one end of the two-dimensional carrier gas channel;
A gate electrode disposed between the source electrode and the drain electrode on the two-dimensional carrier gas channel;
The composition ratio of the composition element between the drain electrode and the gate electrode of the second compound semiconductor layer is the composition ratio of the composition element between the source electrode and the gate electrode of the second compound semiconductor layer. A semiconductor device characterized by being larger than the above. A first compound semiconductor layer having a two-dimensional carrier gas channel;
A second compound semiconductor layer disposed on the first compound semiconductor layer and functioning as a barrier layer;
An anode electrode connected to one end of the two-dimensional carrier gas channel;
A cathode electrode connected to the other end spaced apart from one end of the two-dimensional carrier gas channel,
The composition ratio of the composition element on the anode electrode side between the anode electrode and the cathode electrode of the second compound semiconductor layer is larger than the composition ratio of the composition element on the cathode electrode side. Semiconductor device. A first compound semiconductor layer having a two-dimensional carrier gas channel;
A second compound semiconductor layer disposed on the first compound semiconductor layer and functioning as a barrier layer;
An anode electrode connected to one end of the two-dimensional carrier gas channel;
A cathode electrode connected to the other end spaced apart from one end of the two-dimensional carrier gas channel,
The composition ratio of the composition element on the cathode electrode side between the anode electrode and the cathode electrode of the second compound semiconductor layer is larger than the composition ratio of the composition element on the anode electrode side. Semiconductor device.

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