JP2015207706A - Thin-film lamination structure of compound semiconductor, semiconductor device using the same, and method of manufacturing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film lamination structure of a compound semiconductor that can increase an In composition and that has a structure with reduced dislocation.SOLUTION: Provided is a structure obtained by sequentially laminating a plurality of InGaN layers 5, 9, and 13 by using mask materials 2, 6, and 10. A GaN layer 3 and InGaN layers 7 and 11 are configured by island-like parts with triangular cross sections and that are grown through openings 2a, 6a, 10a of each mask 2, 6, 10, and high-In composition InGaN thin films 5, 9, and 13 are formed thereon. Thereby, threading dislocation existing inside can be extended in parallel to a growth direction, and the dislocation can be reduced. In addition, with respect to the plurality of InGan layers 5, 9, and 13, the In composition becomes larger as it goes above. That is, when a composition of the m-th (m is a natural number) InGaN layer is defined as InGaN, xm<x(m+1) is satisfied in a comparison between In compositions of the m-th InGaN layer and the (m+1)th InGaN layer above the m-th InGaN layer.

Description

  The present invention relates to a compound semiconductor thin film stack structure having a structure for reducing intrinsic defects (dislocations), a semiconductor device, and a method for manufacturing the same, and more particularly, to a semiconductor device having a visible light semiconductor laser using InGaN as a light emitting layer. It is suitable.

  Conventionally, Patent Document 1 proposes a method using lateral selective overgrowth (ELO) as a structure and manufacturing method for improving the quality of a GaN substrate and the like.

  Specifically, a stripe-shaped mask layer is formed on the c-plane of the first Group 3-5 compound semiconductor layer serving as a base crystal with a stripe direction of 0.095 degrees or more and 9.6 degrees from the <1-100> direction. It is formed so as to deviate within the range of less than. The second group 3-5 compound semiconductor layer is selectively grown in the lateral direction on the c-plane using this mask layer. By shifting the stripe direction of the mask layer from a predetermined <1-100> direction within the above-described range, the fluctuation of the c-axis of the required compound semiconductor layer that is selectively grown in the lateral direction on the c-plane of the base crystal is reduced. . For this reason, it is possible to reduce the low-angle grain boundaries generated in the second 3-5 group compound semiconductor layer, and it is possible to improve the quality of the GaN substrate and the like.

Japanese Patent No. 4137633

  However, the manufacturing method described in Patent Document 1 has a problem that the In composition cannot be increased. In addition, there is a problem that the dislocations gathered at the point that the dislocations extended in the horizontal direction by the selective growth in the horizontal direction change the direction in the vertical direction remain on the surface.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide a compound semiconductor thin-film stack structure, a semiconductor device, and a method for manufacturing the same, having a structure in which the In composition can be increased and dislocations are reduced.

  In order to achieve the above object, according to the invention described in claims 1 to 4, a GaN substrate (1) or a substrate composed of a support substrate having a GaN thin film formed on the surface, a plurality of substrates provided on the substrate, A first protective film (2) having an opening (2a) formed thereon, and GaN grown upward from the substrate through a plurality of openings in the first protective film and having a triangular cross section. A plurality of first island-shaped portions (3), a first high In composition InGaN thin film (4) covering the surface of each of the plurality of first island-shaped portions and having a high In composition; A portion in which the In composition is lower than that of the In composition InGaN thin film, is selectively grown in the lateral direction from the first high In composition InGaN thin film, and is selectively grown in the lateral direction from a plurality of adjacent first island-shaped portions. The first InGaN layer ( ), A second protective film (6) provided on the first InGaN layer and having a plurality of openings (6a) formed therein, and the first InGaN through the plurality of openings in the second protective film. A plurality of second island-shaped portions (7) made of InGaN having a triangular cross section and a surface of each of the plurality of second island-shaped portions are covered with a high In composition. The second high In composition InGaN thin film (8), the In composition is lower than the second high In composition InGaN thin film, and laterally selectively grown from the second high In composition InGaN thin film, A second InGaN layer (9) in which the portions grown in the lateral direction from a plurality of adjacent second island-shaped portions are joined together, and the second InGaN layer is more than the first InGaN layer. Is characterized by a high In composition. There.

  In this way, the structure is formed by sequentially stacking a plurality of InGaN layers using a protective film as a mask material. An island-shaped portion having a triangular cross section is formed from the opening of each protective film, and a high In composition InGaN thin film is formed thereon. For this reason, threading dislocations existing inside can be extended parallel to the growth direction, and dislocations can be reduced.

  In addition, with respect to the plurality of InGan layers, the In composition increases as it goes upward. As a result, the In composition can be gradually increased as the layers are stacked, and by increasing the number of stacked layers, an InGaN layer having a higher In composition can be obtained.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

It is sectional drawing which showed the thin film laminated structure of the compound semiconductor concerning 1st Embodiment of this invention. It is sectional drawing which showed the manufacturing process of the thin film laminated structure of the compound semiconductor shown in FIG. It is sectional drawing of the sample used in order to investigate the reduction effect of the number of dislocations in the case of setting it as the structure of 1st Embodiment. It is a figure which shows the result of having investigated the reduction effect of the number of dislocations using the sample shown in FIG. It is sectional drawing of the sample used in order to investigate the direction and number of a dislocation in the case of setting it as the structure of 1st Embodiment. It is a figure which shows the result of having investigated the direction and number of dislocations using the sample shown in FIG. It is sectional drawing of the laser diode to which the thin film laminated structure of the compound semiconductor concerning 2nd Embodiment of this invention was applied. It is sectional drawing of the light emitting diode to which the thin film laminated structure of the compound semiconductor concerning 2nd Embodiment of this invention was applied. It is sectional drawing of HEMT (high electron mobility transistor) to which the thin film laminated structure of the compound semiconductor concerning 2nd Embodiment of this invention was applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
A first embodiment of the present invention will be described. In the present embodiment, a compound semiconductor thin film stack structure having a structure with reduced dislocations suitable for application to a visible light semiconductor laser or the like using InGaN as a light emitting layer and a method for manufacturing the same will be described.

  As shown in FIG. 1, the compound semiconductor thin film laminated structure according to the present embodiment is formed using a GaN substrate 1 as a base material. Here, the GaN substrate 1 is used. However, since the underlying material may be a GaN layer, a sapphire substrate or the like may be used as a support substrate, and a structure in which the GaN layer is formed on the support substrate may be used. On the surface of the GaN substrate 1, a first-layer mask material 2 corresponding to a first protective film in which a plurality of openings 2a are formed apart is formed.

The mask material 2 is made of an insulating film such as a silicon oxide film (SiO ₂ ) or a silicon nitride film (SiN). Although the upper surface shape of the opening 2a formed in the mask material 2 is arbitrary, for example, a circular shape, a square shape, a stripe shape, or the like is used.

  On the surface of the portion of the GaN substrate 1 exposed from the opening 2a of the mask material 2, the GaN layer 3 is selectively grown by epitaxial growth. Since a plurality of openings 2a are formed apart from each other, a plurality of GaN layers 3 are arranged in an island shape and constitute a first island-shaped portion. Since the GaN layer 3 has a lattice constant that matches that of the underlying GaN substrate 1, the occurrence of dislocations at the interface with the GaN substrate 1 is suppressed. In addition, only threading dislocations from the GaN substrate 1 are present. The cross-sectional shape of the GaN layer 3 becomes a triangle by tapering as it goes to the front end side in the growth direction, and threading dislocations existing inside are formed in parallel to the growth direction.

  A high In composition InGaN thin film 4 having an increased In composition is formed on the surface of the GaN layer 3. An InGaN layer 5 is formed from the surface of the high In composition InGaN thin film 4 and the surface of the mask material 2. The high In composition InGaN thin film 4 has a higher In composition than the InGaN layer 5 formed thereon. In the high In composition InGaN thin film 4, since the lattice constant is different from that of the GaN layer 3, dislocations are reduced by complete relaxation.

The InGaN layer 5 corresponds to the first InGaN layer whose composition is In _x1 Ga _(1-x1) N, and is formed by epitaxial growth starting from the high In composition InGaN thin film 4. The InGaN layer 5 is first grown mainly in the lateral direction by lateral selective growth, and the InGaN layers 5 grown laterally from the adjacent high In composition InGaN thin films 4 are united to further upward (vertical direction). It has a grown structure. For this reason, at the same height as the high In composition InGaN thin film 4, the dislocation extends in the lateral direction, and at the position where the InGaN layers 5 that are selectively grown laterally from the adjacent high In composition InGaN thin film 4 are joined together, the dislocation is 1 It is in a state where it gathers at the place and extends upward. Also, dislocations extend upward from the apex position of the high In composition GaN thin film 4 (hereinafter, the dislocations are concentrated in one place and extended upward and the high In composition GaN thin film 4 A location where dislocations extend upward, such as a location where dislocations extend upward from the apex position, is referred to as a “dislocation formation location”. On the surface of the InGaN layer 5, a second mask material 6 corresponding to the second protective film is formed.

The mask material 6 is made of an insulating film such as a silicon oxide film (SiO ₂ ) or a silicon nitride film (SiN). Although the upper surface shape of the opening 6a formed in the mask material 2 is arbitrary, for example, a circular shape, a square shape, a stripe shape, or the like is used. The opening 6a formed in the mask material 6 is formed at a position offset from the opening 2a formed in the first-layer mask material 2 when viewed from the normal direction to the substrate surface. Specifically, the formation position of the opening 6 a is set so that the mask material 6 is present at the dislocation formation location so that the dislocation that has been extended is stopped by the mask material 6.

  An InGaN layer 7 is selectively grown by epitaxial growth on the surface of the portion of the InGaN layer 5 exposed from the opening 6a of the mask material 6. Since a plurality of openings 6a are formed apart from each other, a plurality of InGaN layers 7 are arranged in an island shape, and constitute a second island-shaped portion. Since the InGaN layer 7 has a lattice constant that matches that of the underlying InGaN layer 5, the generation of dislocations at the interface with the InGaN layer 5 is suppressed. When threading dislocations are present in the InGaN layer 5, they are inherited. However, since the mask material 6 is formed at the dislocation formation site, threading dislocations in the InGaN layer 5 are blocked, and the number of dislocations is reduced. Has been reduced. The cross-sectional shape of the InGaN layer 7 becomes a triangle by tapering as it goes to the front end side in the growth direction, and threading dislocations existing inside are formed in parallel to the growth direction.

  On the surface of the InGaN layer 7, a second high In composition InGaN thin film 8 having an increased In composition is formed. An InGaN layer 9 is formed from the surface of the high In composition InGaN thin film 8 and the surface of the mask material 6. The composition of the high In composition InGaN thin film 8 is larger than that of the InGaN layer 9 formed thereon. In the high In composition InGaN thin film 8, since the lattice constant is different from that of the InGaN layer 7, the dislocation is reduced by complete relaxation.

The InGaN layer 9 corresponds to a second InGaN layer having a composition of In _x2 Ga _(1-x2) N, and is formed by epitaxial growth starting from the high In composition InGaN thin film 8. The InGaN layer 9 has the same structure as the InGaN layer 5 described above. However, since the dislocation is reduced by the mask material 6, the InGaN layer 9 is in a state where the dislocation is further reduced than the InGaN layer 5. The InGaN layer 9 has an In composition larger than that of the first InGaN layer 5 (x1 <x2).

  A third-layer mask material 10 corresponding to a third protective film is further formed on the surface of the InGaN layer 9. The mask material 10 is basically configured in the same manner as the first and second mask materials 2 and 6, but the opening 10 a formed in the mask material 10 is the opening 6 a of the mask material 6. The structure is offset from. Thereby, threading dislocations formed in the InGaN layer 9 are further blocked. An InGaN layer 11 is further formed from the opening 10a. This InGaN layer 11 has the same configuration as the InGaN layer 9 and has a triangular cross section like the InGaN layer 7. In addition, since a plurality of openings 10a are formed apart from each other, the plurality of InGaN layers 11 are arranged in an island shape, forming a third island-shaped portion.

Further, a high In composition InGaN thin film 12 having the same configuration as that of the second high In composition InGaN thin film 8 is formed on the surface of the InGaN layer 11. An InGaN layer 13 is formed on the surfaces of the high In composition InGaN thin film 12 and the mask material 10. The InGaN layer 13 corresponds to a third InGaN layer having a composition of In _x3 Ga _(1-x3) N, and is formed by epitaxial growth starting from the high In composition InGaN thin film 8. The InGaN layer 13 has an In composition larger than that of the second InGaN layer 9 (x2 <x3).

  As described above, the compound semiconductor thin film stacked structure according to the present embodiment is configured by sequentially stacking the plurality of InGaN layers 5, 9, and 13 using the mask materials 2, 6, and 10. Then, the GaN layer 3 and the InGaN layers 7 and 11 are formed of island-like portions having a triangular cross section from the openings 2a, 6a, and 10a of the masks 2, 6, and 10, and the high In composition InGaN thin film 5 is formed thereon. 9 and 13 are formed. For this reason, threading dislocations existing inside can be extended parallel to the growth direction, and dislocations can be reduced.

Further, the In composition of the plurality of InGan layers 5, 9, and 13 is increased as it goes to the upper layer. That is, when the composition of the m-th layer (m is a natural number) InGaN layer is In _xm Ga _(1-xm) N, the In composition of the m + 1th layer and the (m + 1) th InGaN layer that is the upper layer is compared. , Xm <x (m + 1). As described above, the In composition is gradually increased as the layers are stacked. Therefore, by increasing the number of stacked layers, an InGaN layer having a higher In composition can be obtained.

  In the present embodiment, three layers of InGaN layers 5, 9, and 13 are stacked. However, this number is arbitrary, and a plurality of layers of two or more layers may be used.

  Next, the manufacturing method of the compound semiconductor thin film laminated structure comprised as mentioned above is demonstrated with reference to FIG.

[Step shown in FIG. 2 (a)]
A GaN substrate 1 is prepared, and an insulating film is formed thereon by, for example, a CVD method to form a first layer mask material 2. Then, the mask material 2 is patterned to form an opening 2a at a desired position. Thereafter, the GaN layer 3 is selectively grown on the surface of the portion of the GaN substrate 1 exposed from the opening 2a of the mask material 2 by epitaxial growth. The GaN layer 3 grown at this time has a triangular cross-sectional shape. In addition, since the lattice constant matches with the underlying GaN substrate 1, the GaN layer 3 is suppressed from generating dislocations at the interface with the GaN substrate 1, and penetrates from the GaN substrate 1. Only dislocations are formed in the GaN layer 3.

  Subsequently, a high In composition InGaN thin film 4 having an increased In composition is grown on the surface of the GaN layer 3. Further, the InGaN layer 5 is grown from the surface of the high In composition InGaN thin film 4 and the surface of the mask material 2.

[Step shown in FIG. 2 (b)]
If the growth of the InGaN layer 5 is continued, the InGaN layer 5 mainly grows in the lateral direction, and dislocations are formed so as to extend according to the crystal orientation in accordance with the growth. Then, InGaN layers 5 that are selectively grown in the lateral direction from adjacent high In composition InGaN thin films 4 are joined together. At this position, dislocations gather in one place.

[Step shown in FIG. 2 (c)]
As the InGaN layer 5 grows upward, dislocations also extend upward. Further, the dislocation extends upward from the apex position of the high In composition GaN thin film 4. In this way, the InGaN layer 5 is grown to a desired thickness.

[Step shown in FIG. 2 (d)]
After the second mask material 6 is formed again by, for example, the CVD method, the same steps as in FIGS. 2A to 2C are performed, so that the InGaN layer 7, the high In composition InGaN thin film 8, and the InGaN layer 9 are processed. Form.

  Although the subsequent steps are not shown in the drawing, the compound semiconductor thin film laminated structure shown in FIG. 1 is completed by performing the same manufacturing steps as in FIGS. 2A to 2C for the third layer. .

  In this manner, the InGaN layers 5, 9, and 13 are stacked and formed so that the InGaN layer can be gradually increased in In composition. At that time, the high In composition InGaN thin films 4, 8 and 12 are inserted under the InGaN layers 5, 9 and 13, so that they exist in lower layers due to complete relaxation due to the difference in lattice constant. It is possible to reduce the dislocation that has been performed.

  Further, by making the GaN layer 3 to be selectively grown first from the opening 2a of the mask material 2 into a triangular cross section, it becomes possible to minimize the upward extension of dislocations only at the apex position and the dislocation formation location. . Further, since the formation positions of the openings 2a, 6a, and 10a of the mask materials 2, 6, and 10 are offset, the dislocations extending upward are blocked by the upper mask material, and the dislocations can be further reduced. become.

  Therefore, it is possible to obtain a compound semiconductor thin film stack structure in which the In composition can be increased and dislocations are reduced.

  As a reference, the effect of the compound semiconductor thin film laminated structure manufactured as described above was confirmed. Specifically, as shown in FIG. 3, a 2.3 μm thick GaN layer 21, a 10 nm thick high In composition InGaN thin film 22, and a 500 nm to 600 nm thick InGaN layer 23 are sequentially formed on a sapphire substrate 20. A film-formed structure was created. Then, the number of dislocations in each structure was examined by SEM (scanning electron microscopy). Further, as a comparative example, the number of dislocations when only the GaN substrate was used and the number of dislocations when the InGaN layer 23 was formed at 888 ° C. when the high In composition InGaN thin film 22 was not formed were also examined. In the case of forming the high In composition InGaN thin film 22, the deposition temperature of the InGaN layer 23 was changed to 888 ° C. and 905 ° C., and the number of dislocations was examined.

  As a result, as shown in FIG. 4, it was confirmed that the number of dislocations was reduced in the case where it was formed compared to the case where the high In composition InGaN thin film 22 was not formed. Moreover, even when the deposition temperature of the InGaN layer 23 changed, the number of dislocations was reduced. In particular, when the film forming temperature was set to 905 ° C., although the size of the dislocation was large, the number of dislocations was reduced as compared with the case where it was set to 888 ° C. Thus, it can be seen that the number of dislocations in the InGaN layer 23 formed thereon can be reduced by inserting the high In composition InGaN thin film 22.

  When the GaN layer 21 is formed on the sapphire substrate 20, the number of dislocations increases. The sapphire substrate 20 is used to facilitate comparison of the number of dislocations between the structure of this embodiment and the conventional structure. However, if the GaN substrate 1 is used as described above, the number of dislocations can be further reduced. Become.

  Further, as shown in FIG. 5, after forming the mask material 32 having the GaN layer 31 and the opening 32a formed on the sapphire substrate 30, a GaN layer 33 is formed from the opening 32a, and further on the mask material 32. A high In composition InGaN thin film 34 and an InGaN layer 35 were stacked. And in this structure, when the cathode luminescence (CL) image was confirmed, the image shown in FIG. 6 was obtained. As shown in this figure, although the upward dislocation extends from the apex of the GaN layer 33 having a triangular cross section, the remaining dislocations extend only in the lateral direction, forming a low dislocation region. It can be confirmed that it is made. This result also shows that the extension of dislocations upwards can be minimized.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, a specific example of a semiconductor device to which the compound semiconductor thin film stacked structure described in the first embodiment is applied will be described.

  FIG. 7 is a cross-sectional view of a chip in which a laser diode using the compound semiconductor thin film laminated structure described in the first embodiment is formed. This laser diode is configured as follows. Specifically, as shown in FIG. 7, a buffer layer 42, an n-type cladding layer 43, a guide layer 44, an active layer 45, an electron blocking layer 46, a guide layer 47, and a p-type cladding are formed on an n-type substrate 41. A layer 48 and a contact layer 49 are formed in this order. A ridge shape is formed by providing a recess 50 that reaches the guide layer 47 through the contact layer 49 and the p-type cladding layer 48, and an insulating film 51 is formed on the surface thereof. Further, the p-type electrode 52 is electrically connected to the contact layer 49 through the contact hole formed in the insulating film 51, and the n-type electrode 53 is electrically connected on the back side of the n-type substrate 41. Yes. A laser diode is configured by such a configuration.

  The buffer layer 42 of the laser diode configured as described above is configured by the compound semiconductor thin film stacked structure described in the first embodiment. Thus, the compound semiconductor thin film laminated structure described in the first embodiment can be applied as the buffer layer 42 in the laser diode.

  Then, the manufacturing method of the laser diode comprised as mentioned above is demonstrated.

  First, an n-type substrate 41 made of n-type GaN is prepared. Then, using this n-type substrate 41 as the GaN substrate 1 described in the first embodiment, and using the manufacturing method described in the first embodiment thereon, for example, a thickness of about 2 μm per layer and a total of about 6 μm. An InGaN layer having a three-layer structure with a thickness of 1 is formed. Thereby, for example, the In composition of the uppermost InGaN layer in the buffer layer 42 can be reduced to about 20%.

Next, an n-type cladding layer 43 made of n-type InGaN is formed on the buffer layer 42. For example, the n-type cladding layer 43 is formed to a thickness of 1 μm, the In composition is about 20%, Si is used as the dopant, and the doping concentration is 1 × 10 ¹⁹ cm ⁻³ . On the n-type cladding layer 43, a guide layer 44 made of non-doped InGaN is formed. For example, the guide layer 44 is formed with a film thickness of 200 nm, and the In composition is about 25%.

Further, on the guide layer 44, a single quantum well composed of a combination of an In _0.3 Ga _0.7 N quantum well layer / In _0.15 Ga _0.85 N barrier layer or a multiple quantum well composed of a plurality of pairs is formed. An active layer 45 is formed. Each quantum well layer and barrier layer are both non-doped. For example, the In composition in each quantum well layer is 40%, the In composition in each barrier layer is 25%, and the film thickness is 3 nm. Is 12 nm.

  Subsequently, an electron block layer 46 composed of non-doped InGaN is formed on the active layer 45. For example, the electron block layer 46 is formed with an In composition of 20% and a film thickness of 15 nm. A guide layer 47 made of non-doped InGaN is formed on the electron block layer 46. For example, the guide layer 44 is formed with a film thickness of 200 nm, and the In composition is about 25%.

Next, a p-type cladding layer 48 made of p-type InGaN is formed on the guide layer 47. For example, the p-type cladding layer 48 is formed with a thickness of 1 μm, the In composition is about 20%, Mg is used as the dopant, and the doping concentration is 5 × 10 ¹⁸ cm ⁻³ . A contact layer 49 made of p-type InGaN is formed on the p-type cladding layer 48. For example, the contact layer 49 is formed to a thickness of 200 nm, the In composition is about 20%, Mg is used as the dopant, and the doping concentration is 5 × 10 ¹⁹ cm ⁻³ .

  Thereafter, by performing dry etching using a desired mask, the concave portion 50 that penetrates the contact layer 49 and the p-type cladding layer 48 and reaches the middle of the guide layer 47 is formed. As a result, a ridge shape having a width of 2 μm is formed at the center of the emission width.

Further, an insulating film 51 made of SiO ₂ , SiN, or the like is formed on the surface, and then patterned using a desired mask to form a contact hole in the insulating film 51 on the contact layer 49. Then, after forming the p-type electrode 52 on the front surface side and the n-type electrode 53 on the back surface side, each process known as a laser diode forming process, that is, cleaving to expose the end face, Then, a step of forming a multilayer film for adjusting the end face reflectance is performed. Finally, the chip of the laser diode shown in FIG. 7 is completed by cutting the chip along the cavity direction.

  As described above, the buffer layer 42 of the laser diode can be configured by the thin film laminated structure of the compound semiconductor described in the first embodiment. In the laser diode configured as described above, a buffer layer 42 in which dislocations are reduced as described in the first embodiment and the In composition is gradually increased can be used. In other words, in a visible light semiconductor laser such as a radar diode having an InGaN light emitting layer, dislocations that impair the performance and longevity of the visible light semiconductor laser are reduced, and the emission wavelength is increased by increasing the In composition. It becomes possible to do.

  As described above, the compound semiconductor thin film stacked structure described in the first embodiment reduces dislocations that impair the performance and longevity of the visible light semiconductor laser in the visible light semiconductor laser using InGaN as the light emitting layer. It can be used as a compound semiconductor thin film stack structure in which the In composition can be increased in order to increase the emission wavelength.

(Third embodiment)
A third embodiment of the present invention will be described. Also in this embodiment, a specific example of a semiconductor device to which the compound semiconductor thin film stacked structure described in the first embodiment is applied will be described.

  FIG. 8 is a cross-sectional view of a chip in which a light emitting diode using the thin film laminated structure of compound semiconductors described in the first embodiment is formed. This light emitting diode is configured as follows. Specifically, as shown in FIG. 8, a GaN template 62, a buffer layer 63, an n-type cladding layer 64, an active layer 65, a p-type cladding layer 66, and a transparent conductive film 67 are formed in this order on an insulating substrate 61. Has been. A recess 68 that penetrates the transparent conductive film 67, the p-type cladding layer 66 and the active layer 65 and reaches the n-type cladding layer 64 is provided, and an insulating film 69 is formed on the surface thereof. Further, the p-type electrode 70 is electrically connected to the transparent conductive film 67 through the contact hole formed in the insulating film 69, and the n-type electrode 71 is electrically connected to the n-type cladding layer 64. ing. A light emitting diode is configured by such a configuration.

  The buffer layer 63 of the light emitting diode having such a configuration is configured by the thin film laminated structure of the compound semiconductor described in the first embodiment. Thus, the compound semiconductor thin film laminated structure described in the first embodiment can be applied as the buffer layer 63 in the light emitting diode.

  Then, the manufacturing method of the light emitting diode comprised as mentioned above is demonstrated.

  First, an insulating substrate 61 composed of a sapphire substrate or the like is prepared. Then, the GaN template 62 is formed on the insulating substrate 61, and the buffer layer 63 is formed thereon by using the manufacturing method described in the first embodiment, for example, with a thickness of 2 μm per layer and a total of about 6 μm. An InGaN layer having a three-layer structure with a thickness of 1 is formed. Thereby, for example, the In composition of the uppermost InGaN layer in the buffer layer 63 can be reduced to about 20%.

Next, an n-type cladding layer 64 made of n-type InGaN is formed on the buffer layer 63. For example, the n-type cladding layer 64 is formed with a thickness of 1 μm, the In composition is about 20%, Si is used as the dopant, and the doping concentration is 1 × 10 ¹⁹ cm ⁻³ . Further, on the n-type cladding layer 64, a single quantum well composed of a combination of In _0.3 Ga _0.7 N quantum well layer / In _0.15 Ga _0.85 N barrier layer or a multiple quantum well composed of a plurality of sets. An active layer 65 is formed. Each quantum well layer and barrier layer are both non-doped. For example, the In composition in each quantum well layer is 40%, the In composition in each barrier layer is 25%, and the film thickness is 3 nm. Is 12 nm.

Subsequently, a p-type cladding layer 66 made of p-type InGaN is formed on the active layer 65. For example, the p-type cladding layer 66 is formed with a thickness of 1 μm, the In composition is about 20%, the dopant is Mg, and the doping concentration is 5 × 10 ¹⁸ cm ⁻³ . A transparent conductive film 67 is formed on the p-type cladding layer 66.

  Thereafter, dry etching using a desired mask is performed to form a recess 68 that penetrates the transparent conductive film 67, the p-type cladding layer 66, and the active layer 65 and reaches the middle of the n-type cladding layer 64.

Further, an insulating film 69 made of SiO ₂ , SiN or the like is formed on the surface, and then patterned using a desired mask, and contacts the insulating film 69 on the transparent conductive film 67 and the n-type cladding layer 64. A hole is formed. Then, the p-type electrode 70 is formed on the surface of the transparent conductive film 67, the n-type electrode 71 is formed on the surface of the n-type cladding layer 64, and finally the chip is cut out, whereby the light emitting diode shown in FIG. The chip is completed.

  As described above, the buffer layer 63 of the light emitting diode can be configured by the thin film laminated structure of the compound semiconductor described in the first embodiment. In the light-emitting diode configured as described above, a buffer layer 63 in which dislocations are reduced as described in the first embodiment and the In composition is gradually increased can be used. That is, dislocations that impair the performance and life of the light-emitting diode are reduced, and the emission wavelength can be increased by increasing the In composition.

  As described above, the compound semiconductor thin film laminated structure described in the first embodiment reduces dislocations that impair the performance and long life of the light-emitting diode in the light-emitting diode using InGaN as the light-emitting layer, and lengthens the emission wavelength. Therefore, it can be used as a compound semiconductor thin film stack structure in which the In composition can be increased.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. Also in this embodiment, a specific example of a semiconductor device to which the compound semiconductor thin film stacked structure described in the first embodiment is applied will be described.

  FIG. 9 is a cross-sectional view of a chip formed with a HEMT using the compound semiconductor thin film stack structure described in the first embodiment. This HEMT is configured as follows. Specifically, as shown in FIG. 9, a GaN template 82, a buffer layer 83, a channel layer 84, and an electron supply layer 85 are sequentially formed on a substrate 81. An insulating film 86 is formed on the surface of the electron supply layer 85. Further, the source electrode 87 and the drain electrode 88 are provided apart from each other so as to penetrate the electron supply layer 85 and be electrically connected to the channel layer 84 through a contact hole formed in the insulating film 86. . A gate electrode 89 electrically connected to the electron supply layer 85 through a contact hole formed in the insulating film 86 is provided between the source electrode 87 and the drain electrode 88. The HEMT is configured by such a configuration.

  The buffer layer 83 in the HEMT having such a configuration is configured by the compound semiconductor thin film stacked structure described in the first embodiment. Thus, the compound semiconductor thin film stack structure described in the first embodiment can be applied as the buffer layer 83 in the HEMT.

  Then, the manufacturing method of HEMT comprised as mentioned above is demonstrated.

  First, a substrate 81 composed of a sapphire substrate or the like is prepared. Then, a GaN template 82 is formed on the substrate 81, and a buffer layer 83 is formed thereon by using the manufacturing method described in the first embodiment, for example, with a thickness of 2 μm per layer and a total of about 6 μm. A three-layer InGaN layer having a thickness is formed. Thereby, for example, the In composition of the uppermost InGaN layer in the buffer layer 83 can be reduced to about 20%.

  Next, a channel layer 84 made of non-doped InGaN is formed on the buffer layer 83. For example, the channel layer 84 is formed with a thickness of 500 nm, and the In composition is about 20%. On the channel layer 84, an electron supply layer 85 made of non-doped GaN is formed with a thickness of 20 nm, for example.

  Further, after an insulating film 86 made of SiN or the like is formed on the surface, patterning is performed using a desired mask, and contact holes are formed in regions where the source electrode 87 and the drain electrode 88 are to be formed. At this time, a recess is provided so as to penetrate the electron supply layer 85 and reach the channel layer 84 at the same time. Then, after the source electrode 87 and the drain electrode 88 are formed, the source electrode 87 and the drain electrode 88 are brought into ohmic contact with the channel layer 84 by performing heat treatment.

  In addition, after the gate electrode 89 in the insulating film 86 is subjected to recess etching, the gate electrode 89 is formed thereon. Finally, by cutting out the chip, the HEMT chip shown in FIG. 9 is completed.

  As described above, the buffer layer 83 of the HEMT can be configured by the compound semiconductor thin film stacked structure described in the first embodiment. The HEMT configured as described above can use a buffer layer 83 in which dislocations as described in the first embodiment are reduced and the In composition is gradually increased. That is, dislocations that impair high performance and long life of the HEMT are reduced.

  As described above, the compound semiconductor thin film stacked structure described in the first embodiment is used as a compound semiconductor thin film stacked structure in which dislocations that impair the performance and long life of the HEMT are reduced in HEMTs using InGaN. Can do.

(Other embodiments)
The present invention is not limited to the embodiment described above, and can be appropriately changed within the scope described in the claims.

  For example, in each of the above-described embodiments, the compound semiconductor thin film stack structure in which three InGaN layers are stacked has been described as an example. However, any structure in which two or more layers are formed may be used. Each time the InGaN layer is stacked, the In composition of the uppermost InGaN layer can be made higher by making the In composition gradually higher.

Specifically, a GaN substrate 1 or a support substrate on which a GaN layer is formed is used as a substrate, and a protective film composed of an insulating film 2 or the like is formed thereon, and a plurality of openings formed in the protective film. A plurality of island-shaped GaN layers 3 having a triangular cross section are formed in the opposite direction to the substrate through the portion. Further, after the high In composition InGaN thin film 4 is formed on the surface of the GaN layer, the InGaN layer 5 is formed by lateral selective growth from the surface of the high In composition InGaN thin film 4. Then, the InGaN layers 5 selectively grown in the lateral direction from the adjacent high In composition InGaN thin films 4 are combined, and then the InGaN layer 5 is grown in the vertical direction. By repeating such steps, the composition of the m-th layer (m is a natural number) InGaN layer is In _xm Ga _(1-xm) N in a compound semiconductor thin film stack structure in which a plurality of InGaN layers are stacked. The composition of the lower high In composition InGaN thin film is In _xm0 Ga _(1-xm0) N, and the following relationship may be established. That is, xm <x (m + 1) is established by comparing the In composition of the m + 1st layer and the (m + 1) th InGaN layer above it, and the In composition of the mth InGaN layer and the high In composition InGaN thin film therebelow And xm <xm0 may be satisfied.

  In the second to fourth embodiments, an example of a semiconductor device to which the compound semiconductor thin film stacked structure described in the first embodiment can be applied has been described. However, the present invention may be applied to semiconductor devices having other structures. good. In the second to fourth embodiments, an example in which the first conductivity type is an n-type and the second conductivity type is a p-type is shown. However, an element of a type in which the conductivity type of each component is inverted. The present invention can also be applied to.

1 GaN substrate 2, 6, 10 Mask material 3 GaN layer 4, 8, 12 High In composition InGaN thin film 5, 7, 9, 11, 13 InGaN layer

Claims (8)

A substrate composed of a GaN substrate (1) or a support substrate having a GaN thin film formed on its surface;
A first protective film (2) provided on the substrate and having a plurality of openings (2a);
A plurality of first island portions (3) made of GaN grown upward from the substrate through the plurality of openings in the first protective film and having a triangular cross section; and
A first high In composition InGaN thin film (4) covering the surface of each of the plurality of first island-shaped portions and having a high In composition;
The In composition is lower than that of the first high In composition InGaN thin film, is selectively grown in the lateral direction from the first high In composition InGaN thin film, and is laterally expanded from the plurality of adjacent first islands. A first InGaN layer (5) in which the directionally grown portions are joined together;
A second protective film (6) provided on the first InGaN layer and having a plurality of openings (6a);
A plurality of second island-shaped portions (7) made of InGaN grown upward from the first InGaN layer through the plurality of openings in the second protective film and having a triangular cross section;
A second high In composition InGaN thin film (8) covering the surface of each of the plurality of second island-shaped portions and having a high In composition;
The In composition is lower than that of the second high In composition InGaN thin film, is selectively grown in the lateral direction from the second high In composition InGaN thin film, and is laterally expanded from the adjacent second island-shaped portions. A second InGaN layer (9) in which the directionally grown portions are joined together,
2. A compound semiconductor thin film stacked structure, wherein the second InGaN layer has an In composition higher than that of the first InGaN layer.   The second protective film, the second island-shaped portion, and the second protective film, the second island-shaped portion further above the second high-In composition InGaN thin film and the second InGaN layer. The same composition as that of the second high In composition InGaN thin film and the second InGaN layer is repeatedly laminated, and the In composition of the InGaN layer is increased as the upper layer is formed. Compound semiconductor thin film stack structure. The composition of the high In composition InGaN thin film in the m-th layer (m is a natural number of 2 or more) of the repeated lamination is In _xm0 Ga _(1-xm0) N, and the composition of the InGaN layer is In _xm Ga _(1-xm). 3. The compound semiconductor thin film stacked structure according to claim 2, wherein the composition of the high In composition InGaN thin film and the InGaN layer in the m-th layer is N, where xm <xm0. The composition of the InGaN layer in the m-th layer (m is a natural number of 2 or more) among the repeatedly stacked layers is In _xm Ga _(1-xm) N, and m + 1 is the upper layer of the m-th layer and the m-th layer. 4. The compound semiconductor thin film multilayer structure according to claim 2, wherein xm <x (m + 1) is established when the composition of the high In composition InGaN thin film in the layer is compared. 5. A thin film laminated structure of a compound semiconductor according to any one of claims 1 to 4 is provided as a buffer layer (42, 63, 83),
A semiconductor device, wherein a semiconductor element is formed on the buffer layer.   The semiconductor device according to claim 5, wherein the semiconductor element is any one of a laser diode, a light emitting diode, and a high electron mobility transistor. A method for producing a thin film multilayer structure of a compound semiconductor according to any one of claims 1 to 4,
Preparing a substrate composed of the GaN substrate or a support substrate having a GaN thin film formed on the surface;
Forming the first protective film having the plurality of openings formed on the substrate;
Epitaxially growing the plurality of first island-shaped portions made of GaN having a triangular cross section through the plurality of openings in the first protective film from the substrate;
Depositing the first high In composition InGaN thin film with a high In composition so as to cover the surface of each of the plurality of first island-shaped portions;
The first InGaN layer having an In composition lower than that of the first high In composition InGaN thin film is laterally selectively grown from the first high In composition InGaN thin film by epitaxial growth, and the plurality of adjacent second layers A step of bringing the portions selectively grown in the horizontal direction from one island-shaped portion together, and then growing further upward;
Forming the second protective film having the plurality of openings formed on the first InGaN layer;
Epitaxially growing the plurality of second island-shaped portions made of InGaN having a triangular cross-section through the plurality of openings in the second protective film from the first InGaN layer;
Depositing the second high In composition InGaN thin film with a high In composition so as to cover the surface of each of the plurality of second island-shaped portions;
The second InGaN layer having an In composition lower than that of the second high In composition InGaN thin film and having an In composition higher than that of the first InGaN layer is epitaxially grown to form the second high In composition InGaN. A step of selectively growing in the lateral direction from the thin film, and combining the portions that have been selectively grown in the lateral direction from the plurality of adjacent second island-shaped portions, and then growing further upward. A method of manufacturing a thin film laminated structure of a compound semiconductor characterized by the above. The compound semiconductor thin film laminated structure formed by using the compound semiconductor thin film laminated structure manufacturing method according to claim 7 is used as a buffer layer (42, 63, 83).
A method of manufacturing a semiconductor device, comprising forming a semiconductor element on the buffer layer.

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