JP4929652B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device having an active layer made of AlGaInP, and more particularly to a surface emitting semiconductor light emitting device having a current diffusion layer made of AlGaAs.

  Recently, the demand for red, yellow, and yellow-green semiconductor light-emitting devices using AlGaInP-based compound semiconductors in the light-emitting layer has increased significantly. The main applications are display indicators for electrical products, numeric keypad lighting for mobile phones, traffic lights, brake lights for automobiles and interior lighting.

  The AlGaInP-based semiconductor light-emitting device has a double heterostructure formed by sequentially growing an n-type GaAs buffer layer, an n-type AlGaInP cladding layer, an AlGaInP active layer, and a p-type AlGaInP cladding layer on an n-type GaAs substrate by MOCVD. It is common to have The resistivity of the p-type AlGaInP cladding layer cannot be lowered sufficiently even when doped with p-type impurities, and since it is difficult to grow a thick AlGaInP film by the MOCVD method, a current is injected into the entire active layer, In order to facilitate the extraction, a current diffusion layer made of AlGaAs or GaP, which is a material different from AlGaInP, is formed on the p-type cladding layer. According to such a structure, the current injected into the p-type layer is supplied to the entire active layer by diffusing the current to the entire layer in the current diffusion layer, so that the entire active layer can emit light. . Further, by increasing the thickness of the current diffusion layer, sufficient current can be diffused, and at the same time, extraction of light from the side surface of the element is promoted. This current spreading layer is sometimes called a window layer or a window layer because the material composition is selected so as to be transparent to the light emitted from the active layer.

  As a material for the current diffusion layer, GaP is mainly used because it is relatively easy to form a thick film by the VPE method and there is little absorption with respect to light on the short wavelength side. However, GaP has a large lattice mismatch with the GaAs substrate and it is difficult to sufficiently increase the crystallinity, and phosphorus-based deposits are deposited inside the reactor and piping of the MOCVD apparatus for thick film growth. For this reason, there are many cases where AlGaAs is selected because the lattice irregularity with the GaAs substrate is small and the maintenance of the apparatus is relatively easy due to the difficulty of maintenance. A semiconductor light emitting device using AlGaAs for the current diffusion layer is disclosed in, for example, Patent Document 1.

  As the p-type dopant of AlGaAs and AlGaInP, zinc (hereinafter referred to as Zn) is often used, but Zn diffuses and penetrates from the p-type current diffusion layer or the p-type cladding layer to the active layer by heat received during crystal growth. There are many cases. It is known that Zn diffused in the active layer forms non-radiative recombination centers and degrades the luminous efficiency of the active layer. The influence of such non-radiative recombination centers due to Zn becomes even more pronounced when the light emitting element is continuously energized, and the reliability of the light emitting element is significantly deteriorated.

  In order to solve such a problem, for example, Patent Document 2 proposes a method of forming a part of the p-type cladding layer on the active layer side substantially non-doped (hereinafter referred to as a first method). ing. According to this method, even if Zn is diffused from the p-type current diffusion layer, it is diffused only to the non-doped cladding layer and hardly diffuses to the active layer, thereby suppressing reduction in luminous efficiency due to Zn diffusion. It is supposed to be possible.

  However, if the cladding layer is non-doped in this way, the diffusion of Zn into the active layer is certainly reduced, but the Zn diffused in the cladding layer affects the light emission efficiency, and the light emitting state of the light emitting element is uneven. The inventors have found. Although details of the cause are unknown, it is presumed that the diffused Zn does not work as an acceptor inside the cladding layer.

  On the other hand, Patent Document 3 proposes a method (hereinafter referred to as a second method) in which a p-type current diffusion layer made of AlGaAs has a multilayer structure of four or more layers of semiconductor materials having different compositions. According to this method, even if the current diffusion layer is trapped at the interface inside the multilayer structure and the current diffusion layer has a high carrier concentration, the dopant does not diffuse into the active layer, so that efficient current diffusion, reduction of operating voltage, and high light output can be realized. It is said that.

  However, the present inventors have found a problem that when the current diffusion layer is formed using such a method, the growth lot generates a light output that is greatly reduced by continuous energization. The cause of this is unknown, but it is presumed that the dopant trapped at the interface could not stay inside the multilayer structure due to fluctuations in growth conditions but diffused into the active layer.

  On the other hand, in Patent Document 4, the p-type AlGaAs window layer, that is, the p-type impurity concentration in the portion near the active layer of the p-type AlGaAs current diffusion layer is lowered and the p-type impurity concentration in the portion far from the active layer is increased. A method (hereinafter referred to as a third method) has been proposed. According to this method, by suppressing the diffusion of p-type impurities into the active layer, the generation of non-radiative recombination centers in the active layer can be prevented, and the p-type impurities at a portion far from the active layer can be increased. Since the resistivity of the current diffusion layer can be lowered, it is said that a light-emitting element with high luminance and excellent reliability can be provided.

Certainly, according to this method, it is possible to obtain a light emitting device having higher luminance and higher reliability than conventional ones. However, if the p-type impurity concentration of the current diffusion layer is increased in order to further increase the luminance, current can be applied. Although the previous light output is increased, the problem that the light output is significantly reduced by continuous energization is unavoidable. When the p-type impurity concentration is lowered in order to suppress a decrease in light output due to continuous energization, the deterioration in energization is improved, but the light output before energization cannot be increased. That is, the present inventors have found that there is a problem that there is a trade-off between the light output before and after energization regarding the p-type impurity concentration of the current diffusion layer.
JP-A-3-171679 JP-A-8-293623 Japanese Patent Laid-Open No. 2002-164568 JP-A-5-335619

  None of the methods described in the above-mentioned publications can sufficiently avoid the diffusion of Zn from the p-type AlGaAs current diffusion layer due to heat during crystal growth or continuous energization of the light-emitting element. At present, sufficient measures have not been taken to reduce the luminous efficiency due to the formation of Zn-related non-radiative recombination centers in the cladding layer.

  Accordingly, the present invention has been made to solve such a problem, and suppresses formation of non-radiative recombination centers in the active layer due to Zn diffusion from the p-type AlGaAs current diffusion layer, thereby increasing the brightness. A highly reliable semiconductor light emitting device is provided.

  As a result of intensive studies on the layer structure and the Zn concentration of the p-type AlGaAs current diffusion layer, the present inventors have increased the light output before energization and the continuous energization with respect to the Zn concentration of the current diffusion layer having a two-layer structure. The present inventors have found a condition for suppressing a decrease in light output and have made the present invention.

  The semiconductor light emitting device of the present invention has an n-type cladding layer made of AlGaInP, an active layer, a p-type cladding layer, and a current diffusion layer made of AlGaAs on a GaAs substrate, and Zn as a p-type impurity in the current diffusion layer. A doped semiconductor light emitting device, wherein the current diffusion layer includes at least two layers of a first current diffusion layer and a second current diffusion layer having different Zn concentrations from the side close to the active layer, The Zn concentration of the current diffusion layer is higher than the Zn concentration of the second current diffusion layer.

  Conventionally, in a semiconductor light-emitting device using Zn as a p-type dopant, the diffusion of Zn from the AlGaAs current diffusion layer to the active layer cannot be sufficiently prevented despite the proposed method described above. In many cases, countermeasures such as using a dopant such as magnesium or carbon having a small diffusion coefficient have been taken. However, magnesium has poor controllability in crystal growth, such as memory effect and doping delay, and carbon has problems such as difficulty in controlling the doping level, resulting in a bad production yield. It was.

  According to the present invention, Zn having good controllability in crystal growth can be used as the p-type dopant of the current diffusion layer, so that a high-brightness and high-reliability semiconductor device can be obtained by preventing Zn diffusion into the active layer. There is an effect that it can be manufactured without lowering.

  A first invention of the present application has an n-type cladding layer made of AlGaInP, an active layer, a p-type cladding layer, and a current diffusion layer made of AlGaAs on a GaAs substrate, and the current diffusion layer contains Zn as a p-type impurity. A doped semiconductor light emitting device, wherein the current diffusion layer includes at least two layers of a first current diffusion layer and a second current diffusion layer having different Zn concentrations from the side close to the active layer, The semiconductor light emitting device is characterized in that the Zn concentration of the current diffusion layer is higher than the Zn concentration of the second current diffusion layer. With this configuration, the light output before energization can be increased, and at the same time, a decrease in light output due to continuous energization can be suppressed.

According to a second invention of the present application, in the invention according to claim 1, the Zn concentration of the first current diffusion layer is set in a range of 4 × 10 ¹⁸ / cm ³ or more and 2 × 10 ¹⁹ / cm ³ or less. The thickness of the first current diffusion layer is set in the range of 0.5 μm to 3 μm. With this configuration, the light output before energization can be increased.

According to a third invention of the present application, in the invention according to claim 1 or 2, the Zn concentration of the second current diffusion layer is set in a range of 5 × 10 ¹⁷ / cm ³ or more and less than 3 × 10 ¹⁸ / cm ^3. This is a semiconductor light-emitting element. With this configuration, the diffusion of Zn into the active layer can be suppressed without impairing the current spread in the current diffusion layer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view of a semiconductor light emitting device according to an embodiment of the present invention. In FIG. 1, an n-type GaAs buffer layer 2, an n-type Al _0.35 Ga _0.15 In _0.5 P cladding layer 3, an undoped Al _0.05 Ga _0.45 In _0.5 P active layer 4, a p-type Al _0.35 Ga _0.15 In _{A 0.5} P clad layer 5 and a p-type Al _0.7 Ga _0.3 As current diffusion layer 6 are formed. These layer structures are grown by MOCVD, and the current diffusion layer 6 is doped with Zn as a p-type impurity. The current diffusion layer 6 has a two-layer structure of a first current diffusion layer 7 and a second current diffusion layer 8 having different Zn concentrations from the side close to the active layer 4. A p-side electrode 9 for bonding is formed on a part of the second current diffusion layer 8. The region where the p-side electrode 9 is not formed on the second current diffusion layer 8 and the side surface portion of the current diffusion layer 6 are substantially light emitting surfaces. An n-side electrode 10 is formed on the surface of the n-type GaAs substrate 1 opposite to the n-type GaAs buffer layer 2.

  The first feature of the present invention is that the Zn concentration of the first current diffusion layer 7 is higher than the Zn concentration of the second current diffusion layer 8. The details of the reason why it is possible to increase the light output before energization and to suppress the decrease in the light output due to continuous energization by such a configuration is unknown, but it is presumed as follows Can do.

  Comparing the present invention with the prior art, the first method, the second method, and the third method described above are relatively adjacent to the current diffusion layer doped with Zn at a relatively high concentration. A p-type cladding layer having a low Zn concentration or a current diffusion layer having a low Zn concentration is formed. In such a configuration in which the Zn concentration in the layer closer to the active layer is lowered and the Zn concentration in the current diffusion layer far from the active layer is increased, there is a large concentration difference between the two layers. It is considered that the concentration difference becomes a driving force for diffusion, and tends to produce an effect of promoting diffusion to the active layer side.

  In contrast, in the present invention, the Zn concentration of the current diffusion layer closer to the active layer is increased and the Zn concentration of the current diffusion layer closer to the active layer is decreased. Diffusion occurs toward the current diffusion layer. For this reason, it is considered that Zn diffusion to the active layer side is reduced, and formation of non-radiative recombination centers in the active layer and the p-type cladding layer is suppressed. Furthermore, since the Zn concentration of the current diffusion layer closer to the active layer can be increased, the light output can be increased.

The second feature of the present invention is that the Zn concentration of the first current diffusion layer is set in the range of 4 × 10 ¹⁸ / cm ³ or more and 2 × 10 ¹⁹ / cm ³ or less, and the first current diffusion is performed. The thickness of the layer is set in the range of 0.5 μm to 3 μm. When the Zn concentration of the first current diffusion layer is smaller than 4 × 10 ¹⁸ / cm ³ , the light output before energization cannot be increased although the decrease in light output due to continuous energization is small. On the other hand, if it is higher than 2 × 10 ¹⁹ / cm ³ , the light output before energization can be increased, but the light output is reduced by continuous energization. On the other hand, when the thickness of the first current diffusion layer is thinner than 0.5 μm, the light output before energization cannot be increased although the decrease in the light output due to continuous energization is small. On the other hand, if it is thicker than 3 μm, it becomes close to the case where the current diffusion layer is composed of a single layer with a high Zn concentration, so that the light output is reduced due to continuous energization.

The third feature of the present invention is that when the Zn concentration and thickness range of the first current diffusion layer is set as described above, the Zn concentration of the second current diffusion layer is 5 × 10 ¹⁷ / cm ³ or more 3 It is set within a range of less than × 10 ¹⁸ / cm ³ . When the Zn concentration of the second current diffusion layer is lower than 5 × 10 ¹⁷ / cm ³ , the current spread is deteriorated and light is emitted only near the p-side electrode, so that the light output cannot be increased. On the other hand, when it becomes higher than 3 × 10 ¹⁸ / cm ³ , there is a tendency that a decrease in light output due to continuous energization becomes remarkable.

  In addition, it is preferable that the thickness of the p-type cladding layer 5 is set in the range of 0.5 μm to 3.0 μm in order to sufficiently achieve the effects of the present invention. If the thickness is less than 0.5 μm, the margin for an increase in Zn diffusion due to fluctuations in growth conditions decreases and the light output tends to decrease. On the other hand, when the thickness is larger than 3.0 μm, the growth time of the p-type cladding layer itself becomes longer, and the decrease in light output due to the diffusion of the p-type impurities doped in the p-type cladding layer into the active layer tends to become remarkable. There is.

  As described above, by specifying the requirements for the first current diffusion layer, the second current diffusion layer, and the p-type cladding layer, the effect of the present invention can be more remarkably exhibited.

  In the present embodiment, the current diffusion layer has been described as being composed of two layers, the first current diffusion layer and the second current diffusion layer. For example, a third current diffusion layer is further formed on the second current diffusion layer. Even when a layer having a different Zn concentration is provided as the current diffusion layer, the third current diffusion layer is not set to a Zn concentration or thickness enough to diffuse to the first current diffusion layer or the p-type cladding layer. It is included in the scope of the idea of the present invention.

  The active layer may have a multiple quantum well structure in which well layers and barrier layers are alternately stacked, and a distributed Bragg reflection layer in which layers having different refractive indexes are alternately stacked between a substrate and an n-type cladding layer. It may be formed.

  As an example of the present invention, a method for manufacturing the semiconductor light emitting element shown in FIG. 1 will be described.

(Example)
First, an n-type GaAs buffer layer 2, an n-type Al _0.35 Ga _0.15 In _0.5 P cladding layer 3, an undoped Al _0.05 Ga _0.45 In _0.5 P active layer 4 are formed on an n-type silicon (Si) doped GaAs substrate 1 by MOCVD. Then, the p-type Al _0.35 Ga _0.15 In _0.5 P clad layer 5 is grown sequentially. Hydrogen diluted monosilane (SiH ₄ ) is used as the n-type impurity material, but hydrogen selenide can also be used. Trimethylaluminum, trimethylgallium, trimethylindium and phosphine are used as the raw materials for Al, Ga, In and P, respectively. Thereafter, a p-type Al _0.7 Ga _0.3 As current diffusion layer 6 is continuously grown on the p-type cladding layer 5. The current diffusion layer has a two-layer structure in which a first current diffusion layer 7 having a high Zn concentration and a second current diffusion layer 8 having a low Zn concentration are continuously grown from the side close to the active layer. The thicknesses of the p-type cladding layer, the first current diffusion layer, and the second current diffusion layer were 1.0 μm, 2.0 μm, and 5.0 μm, respectively.

  The MOCVD growth from the n-type buffer layer to the p-type cladding layer is performed at a growth temperature of about 660 ° C., a growth pressure of 76 Torr, and the growth rate of each layer is 15 nm / min to 20 nm / min. The ratio of the supply amount, that is, the V / III ratio was 150 to 200.

  The current diffusion layer was grown at a growth temperature of about 660 ° C., a growth pressure of 76 Torr, a growth rate of about 80 nm / min, and a V / III ratio of about 50. The Zn concentration is adjusted by appropriately changing the flow rate of bubbling hydrogen of dimethyl zinc, which is a Zn raw material.

  After the growth of the current diffusion layer is finished, AuGeNi is formed on the entire surface of the wafer on the n-type GaAs substrate side, AuZn is formed on the entire surface of the current diffusion layer side by vapor deposition, and AuZn on the current diffusion layer side is formed. The film was patterned by photolithography to form an n-side electrode on the n-type GaAs substrate side and a p-side electrode on the current diffusion layer side. Thereafter, the semiconductor light emitting device according to the present invention is obtained by separating the wafer into individual chips by dicing.

FIG. 2 is a graph showing the Zn concentration range of the first current diffusion layer and the second current diffusion layer of the semiconductor light emitting device according to the embodiment of the present invention. The Zn concentration is measured by secondary ion mass spectrometry. For example, “1E + 18” indicates 1 × 10 ¹⁸ in the density notation.

  Using the manufacturing method of this example, the Zn concentrations of the first current diffusion layer and the second current diffusion layer are adjusted so that the Zn concentration is in the range shown by the hatched portion in FIG. When the element was fabricated and mounted on the stem and the characteristics were evaluated, the light output before energization was as high as 2.2 to 2.8 mW. Further, when this semiconductor light emitting device was continuously energized at a forward current of 50 mA, the ratio of the light output after 500 hours of energization to the light output before energization, that is, the residual luminance ratio was about 96 to 104%. It was good. Note that substantially the same results were obtained when the thickness of the p-type cladding layer was set in the range of 0.5 μm to 3.0 μm.

(Comparative example)
For comparison, a semiconductor light emitting device was fabricated in the same manner as in the example except that the conditions of Zn concentration in the range shown in A, B, C, and D of FIG. 2 were used, and the light output before energization and 500 hours after energization The remaining luminance rate was evaluated. Conditions A and B correspond to those using the third method described above. The semiconductor light emitting device using the condition A had a light output before energization of 1.2 mW and a luminance residual ratio of 85%. The condition of B was an optical output of 0.8 mW and a luminance residual ratio of 90%. On the other hand, the condition of C was an optical output of 1.5 mW and the remaining luminance rate was 60%, and the condition of D was an optical output of 1.7 mW and a remaining luminance rate of 70%.

  The present invention includes two current diffusion layers having different Zn concentrations, and by increasing the Zn concentration on the side closer to the active layer, the light output can be increased and at the same time the reduction of the light output due to continuous energization is suppressed. It can also be applied to applications that require.

1 is a schematic cross-sectional view of a semiconductor light emitting device according to an embodiment of the present invention. The graph which shows the range of Zn density | concentration of the 1st current spreading layer and the 2nd current spreading layer of the semiconductor light-emitting device concerning one embodiment of the present invention

Explanation of symbols

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type Al _0.35 Ga _0.15 In _0.5 P clad layer 4 undoped Al _0.05 Ga _0.45 In _0.5 P active layer 5 p-type Al _0.35 Ga _0.15 In _0.5 P clad layer 6 p-type Al _0.7 Ga _0.3 As current spreading layer 7 first current spreading layer 8 second current spreading layer 9 p-side electrode 10 n-side electrode

Claims (2)

A semiconductor light emitting device having an n-type cladding layer made of AlGaInP, an active layer, a p-type cladding layer, and a current diffusion layer made of AlGaAs on a GaAs substrate, wherein the current diffusion layer is doped with Zn as a p-type impurity. The current spreading layer includes at least two layers of a first current spreading layer and a second current spreading layer having different Zn concentrations from the side close to the active layer, and the first current spreading layer has a Zn concentration of the first current spreading layer. rather higher than the Zn concentration of the second current spreading layer,
The Zn concentration of the first current spreading layer is set in a range of 4 × 10 ¹⁸ / cm ³ or more and 2 × 10 ¹⁹ / cm ³ or less, and the thickness of the first current spreading layer is 0.5 μm. To 3 μm . A semiconductor light emitting device characterized by being set in a range of 3 μm to 3 μm . 2. The semiconductor light emitting element according to claim 1, wherein the Zn concentration of the second current diffusion layer is set in a range of 5 × 10 ¹⁷ / cm ³ or more and less than 3 × 10 ¹⁸ / cm ³ .

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