JP2006210630A - Group iii nitride semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain impurities from diffusing into an active layer so as to provide a group III nitride semiconductor laser device which is kept stable in optical output characteristics and excellent in reliability as a result. <P>SOLUTION: The group III nitride semiconductor laser device has a configuration in which a p-type impurity diffusion restricting layer 7 that has an electrical field which extends from a p-type clad layer 10 toward the active layer 5 in an equilibrium state is provided between the active layer 5 and the p-type clad layer 10, so that the electrical field functions as a means for pulling back the p-type impurities which are turned negative ions toward the p-type clad layer 10. The p-type impurities can be restrained from diffusing, the diffusion of the p-type impurities can be controlled, and as a result the group III nitride semiconductor laser device can be provided which is stable in optical output characteristics and excellent in reliability. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device using a group III nitride semiconductor.

  In recent years, there has been a growing demand for semiconductor laser devices that output blue-violet light as light sources for next-generation high-density optical disks, and light emission made of group III nitride semiconductors, which are direct transition semiconductors with a forbidden bandwidth ranging from 1.9 eV to 6.2 eV. Research and development of equipment is actively conducted.

In a laser device made of a group III nitride semiconductor, AlGaN containing Al in the cladding layer is often used, but with such a crystal, it becomes difficult to generate p-type carriers as the Al composition ratio increases. Tend. Therefore, a high-concentration p-type impurity exceeding 10 ¹⁸ cm ⁻³ is added to the p-type cladding layer. In addition, in order to suppress leakage of electrons from the active layer to the p-type cladding layer, an electron block layer made of AlGaN having an Al composition ratio larger than that of the p-type cladding layer may be provided before the p-type cladding layer. However, a high-concentration p-type impurity is also added to this layer.

On the other hand, high-concentration p-type impurities cause light absorption loss, and when diffused in the active layer, they can form defect levels and deteriorate laser characteristics.
Conventionally, there has been disclosed a structure in which a p-side cladding layer is constituted by a stack of an n-type layer and a p-type layer and a distance is provided between the active layer and the p-type layer.

Hereinafter, a conventional group III nitride semiconductor laser device will be described with reference to FIG.
FIG. 12 is a cross-sectional view showing the structure of a conventional group III nitride semiconductor laser device.
As shown in FIG. 12, the conventional III-nitride semiconductor laser device includes an n-type contact layer 102, an n-type cladding layer 103, an undoped n-side light guide layer 104, and a multiple quantum well (epitaxially grown) grown on a sapphire substrate 101. MQW) Insulating film with a laminated structure comprising an active layer 105, an undoped p-side light guide layer 106, an undoped p-side first cladding layer 108, a p-type electron blocking layer 109, a p-type second cladding layer 110, and a p-type contact layer 111 112, a p-side electrode 113 and an n-side electrode 114 are provided (see, for example, Patent Document 1).

However, the above structure may be intended to reduce the operating voltage, and the direction and magnitude of the electric field that has a great influence on the diffusion of ionized impurities is not considered.
JP 2003-289176 A

  An object of the present invention is to provide a group III nitride semiconductor laser device having stable light output characteristics by suppressing diffusion of p-type impurities into an active layer and, as a result, having high reliability. To do.

  In order to achieve the above object, a group III nitride semiconductor laser device according to claim 1 of the present invention is provided in a direction from the p-type cladding layer to the active layer at least in an equilibrium state between the active layer and the p-type cladding layer. It includes a p-type impurity diffusion suppression layer having an electric field toward it.

The group III nitride semiconductor laser device according to claim 2, wherein an n-type group III nitride semiconductor region provided with an n-side electrode, a p-type group III nitride semiconductor region provided with a p-side electrode and provided with a cladding layer, An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region, the active layer, and the p-type group III nitride semiconductor region And a p-type impurity diffusion suppression layer composed of Al _x1 Ga _1-x1-y1 In _y1 N (x1 + y1 ≦ 1).

The group III nitride semiconductor laser device according to claim 3, wherein an n-type group III nitride semiconductor region provided with an n-side electrode, a p-type group III nitride semiconductor region provided with a p-side electrode and provided with a cladding layer, An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region, the active layer, and the p-type group III nitride semiconductor region Between the first p-type impurity diffusion suppression layer composed of Al _x1 Ga _1-x1-y1 In _y1 N (x1 + y1 ≦ 1), and the active layer and the first p-type impurity diffusion suppression layer And a second p-type impurity diffusion suppression layer composed of Al _x2 Ga _1-x2-y2 In _y2 N (x2 + y2 ≦ 1).

The group III nitride semiconductor laser device according to claim 4, wherein an n-type group III nitride semiconductor region provided with an n-side electrode, a p-type group III nitride semiconductor region provided with a p-side electrode and provided with a cladding layer, An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region, the active layer, and the p-type group III nitride semiconductor region A p-type impurity diffusion suppression layer composed of Ga _1-y1 In _y1 N (0 <y1 ≦ 1), and the p-type impurity diffusion suppression layer in the p-type group III nitride semiconductor region, The adjacent region is a GaN layer.

The group III nitride semiconductor laser device according to claim 5, wherein an n-type group III nitride semiconductor region provided with an n-side electrode, a p-type group III nitride semiconductor region provided with a p-side electrode and provided with a cladding layer, An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region, the active layer, and the p-type group III nitride semiconductor region A first p-type impurity diffusion suppression layer composed of a plurality of layers of Al _xan1 Ga _1-xan1-yan1 In _yan1 N (layers n1 = 1, 2,..., M1, xan1 + yan1 ≦ 1), and a _{Al x2 Ga 1-x2-y2} in y2 N (x2 + y2 ≦ 1) second p-type impurity diffusion suppression layer composed between the active layer and the first p-type impurity diffusion suppression layer , The strain amount of the second p-type impurity diffusion suppression layer is the first Characterized in that does not exceed the amount of strain type impurity diffusion suppression layer.

  The group III nitride semiconductor laser device according to claim 6 is the group III nitride semiconductor laser device according to claim 5, wherein the In composition ratio of the first p-type impurity diffusion suppression layer is set to the second p-type impurity. It is characterized by being larger than the In composition ratio of the diffusion suppressing layer.

  The group III nitride semiconductor laser device according to claim 7 is the group III nitride semiconductor laser device according to claim 5, wherein the number m of layers is 5 or less. .

  The group III nitride semiconductor laser device according to claim 8 is the group III nitride semiconductor laser device according to any one of claims 5, 6, or 7, wherein the second p-type impurity diffusion suppression layer is used. An n-type impurity is added to at least a part of the structure.

  As described above, by suppressing the diffusion of the p-type impurity into the active layer, it is possible to provide a group III nitride semiconductor laser device having stable light output characteristics and, as a result, having high reliability.

  In the semiconductor laser device according to the present invention, a p-type impurity diffusion suppression layer having an electric field from the p-type cladding layer toward the active layer in at least an equilibrium state is provided between the active layer and the p-type cladding layer. This electric field works to pull back the p-type impurities that are negative ions in the direction of the p-type cladding layer and can suppress the diffusion of the p-type impurities, so that the control of the p-type impurities becomes possible and stable. As a result, it is possible to provide a group III nitride semiconductor laser device having high light output characteristics and high reliability.

  The group III nitride semiconductor laser device of the present invention has a p-type electric field (hereinafter referred to as a negative electric field) between the active layer and the p-type cladding layer at least in an equilibrium state from the p-type cladding layer toward the active layer. A type impurity diffusion suppression layer is provided.

  Since the p-type impurity becomes negative ions due to the emission of holes, the negative electric field existing between the active layer and the p-type cladding layer works to pull the p-type impurity back toward the p-type cladding layer. Diffusion of type impurities into the active layer can be suppressed.

The semiconductor laser device of the present invention has a p-type impurity diffusion suppression layer made of Al _x1 Ga _1-x1-y1 In _y1 N between the active layer and the p-type cladding layer, and the Al _x1 Ga _1-x1- Al _x2 Ga _1-x2-y2 In _y2 N is disposed between _y1 In _y1 N and the active layer in contact with the Al _x1 Ga _1-x1-y1 In _y1 N, and the Al _x1 Ga _{1-x1- y1} an in _y1 N has a compressive strain, is configured to further distortion amount of the _{Al x2 Ga 1-x2-y2} in y2 N it does not exceed the amount of strain _{Al x1 Ga 1-x1-y1} in y1 N.

Since the AlGaInN-based material has a characteristic that the natural polarization _Psp and the piezopolarization _Ppz are larger than those of other III-V group semiconductors, the magnitude and polarity of the electric field can be controlled using these polarizations. Can do. The size of P _sp is uniformly determined by the material, but P _pz is the in-plane strain ε ₁ (= (a−a ₀ ) / a ₀ , a: in-plane lattice constant in the strain state, a ₀ : In-plane lattice constant in a relaxed state).

P _pz = 2ε ₁ * (e ₃₁ −e ₃₃ * C ₁₃ / C ₃₃ ) (1)
e ₃₁ , e ₃₃ : Piezoelectric coefficient
C ₁₃ , C ₃₃ : Elastic constant From the equation (1), it can be seen that the magnitude of P _pz increases in proportion to the amount of strain, and its sign is determined by the direction of strain. In AlGaInN-based materials, the parentheses in the formula (1) must be negative (reference: O. Ambacher et al., J. Phys .: Condens. Matter, Vol. 14, 3399-3434 (2002)). , P _pz is positive for compressive strain and negative for tensile strain.

The charge induced by the polarization P (= P _sp + P _pz ) is expressed by the following equation:
ρ _P = −∇P (2)
_{Al x1 Ga 1-x1-y1} In y1 N / Al x2 Ga 1-x2-y2 In y2 N hetero interface _{(Al x1 Ga 1-x1-} y1 In y1 N upper _{layer, Al x2 Ga 1-x2-} y2 In y2 In the case where N is the lower layer, a fixed charge as shown by the following formula is induced.

σ = P ₂ −P ₁
= (P _SP2 + P _PZ2 ) − (P _SP1 + P _PZ1 )
= (P _SP2 -P _SP1 ) + (P _PZ2 -P _PZ1 ) (3)
Here, representing the polarization of each _{P 1} and _{P 2 Al x1 Ga 1-x1-y1} In y1 N and _{Al x2 Ga 1-x2-y2} In y2 N.

In order to generate a negative electric field in the Al _x1 Ga _1-x1-y1 In _y1 N layer, it is necessary to make the σ negative. Since the hetero interface is formed of a semiconductor layer made of the same material, it can be considered that the difference between P _SP1 and P _SP2 is small. Therefore, in order to make σ negative, P _PZ1 is positive and P _PZ2 <P _PZ1 may be satisfied. _{That, Al x1 Ga 1-x1-} y1 In y1 N has a compressive _strain, Al _x2 strain of the _{Ga 1-x2-y2 In y2} N exceeds the _{Al x1 Ga 1-x1-y1} In y1 N strain of By avoiding this, a negative electric field can be realized.

In this case, p-type impurity diffusion suppression layer is composed of _{Ga 1-y} In y N layer, in contact with the _{Ga 1-y} In y N between the active layer and the _{Ga 1-y} In y N GaN is disposed, and the In composition ratio y of the Ga _1-y In _y N is preferably 0.03 or more. This configuration is the combination with the smallest number of elements that can realize a negative electric field in this material system, and can be most easily manufactured.

The p-type impurity diffusion suppression layer is composed of a plurality of Al _xan Ga _1-xan-yan In _yan N layers (n = 1, 2,..., M), and the Al _xan Ga _1-xan-yan In layer is formed. Al _xbn Ga _1-xbn-ybn In _ybn N layer (n = 1, 2,... in contact with each Al _xan Ga _1-xan-yan In _yan N layer between the _yan N layer and the active layer M), the Al _xan Ga _1-xan-yan In _yan N layer has compressive strain, and the strain amount of each Al _xbn Ga _1-xbn-ybn In _ybn N layer is p-type cladding layer A structure that does not exceed the amount of strain of the Al _xan Ga _1-xan-yan In _yan N layer in contact with each other may be used. By making the p-type impurity diffusion suppression layer thinner and multi-layered, a higher negative electric field can be obtained, and the diffusion suppression effect of the p-type impurity can be enhanced.

In this case, the number m of the Al _xan Ga _1-xan-yan In _yan N layer is desirably 5 or less. When m is 5 or less, the effect of suppressing the diffusion of p-type impurities can be enhanced while suppressing an increase in device resistance.

Further, Al _xbn Ga _1-xbn arranged in contact with each Al _xan Ga _1-xan-yan In _yan N layer (n = 1, 2,..., _M ) constituting the p-type impurity diffusion suppression layer. _-Ybn In _{ybn An} n-type impurity may be added to at least a part of the N layer (n = 1, 2,..., _M ). Since the effect of suppressing the diffusion of the p-type impurity is also expected for the n-type impurity, the effect of suppressing the diffusion of the p-type impurity can be enhanced by a synergistic effect with the negative electric field.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a cross-sectional view showing the configuration of the semiconductor laser device according to the first embodiment, and FIG. 2 is a diagram showing the electric field distribution of the semiconductor laser device according to the first embodiment.
First, a method for manufacturing the semiconductor laser device in the first embodiment will be described.

  First, a substrate 1 made of sapphire having a diameter of about 51 mm (2 inches) is prepared, and the surface thereof is washed with an acidic aqueous solution. Subsequently, the cleaned substrate 1 is held on, for example, a susceptor in a reaction furnace of a metal organic chemical vapor deposition (MOVPE) apparatus, and the reaction furnace is evacuated to a vacuum. Subsequently, the inside of the reaction furnace is set to a hydrogen atmosphere having a pressure of about 300 × 133.322 Pa (300 Torr), the temperature is raised to about 1100 ° C., the substrate 1 is heated, and the substrate surface is thermally cleaned for about 10 minutes.

Next, after the temperature of the reaction furnace is lowered to about 500 ° C., trimethylgallium (TMG) with a supply amount of about 25 μmol / min and ammonia (NH ₃ ) with a supply amount of about 7.5 L / min on the substrate 1. By simultaneously supplying a gas and a carrier gas made of hydrogen, a low-temperature buffer layer (not shown) made of gallium nitride (GaN) having a thickness of about 20 nm is grown. At this time, the value of the supply ratio between the ammonia gas as the group V material and the TMG as the group III material is about 6500.

Subsequently, the temperature in the reaction furnace is raised to about 1000 ° C., and while supplying silane (SiH ₄ ) gas as an n-type dopant, a thickness of about 4 μm is formed on a low-temperature buffer layer (not shown). Then, an n-type contact layer 2 made of n-type GaN having a silicon (Si) impurity concentration of about 1 × 10 ¹⁸ cm ⁻³ is grown. Subsequently, while also supplying trimethylaluminum (TMA) as a group III material on the n-type contact layer 2, the n-type having a thickness of about 1.2 μm and an Si impurity concentration of about 5 × 10 ¹⁷ cm ⁻³ . An n-type cladding layer 3 made of Al _0.05 Ga _0.95 N is grown.

Thereafter, on the n-type cladding layer 3, n-type GaN having a thickness of about 90 nm and an Si impurity concentration of about 1 × 10 ¹⁷ cm ⁻³ and Ga _0.98 In _{0. The} n-side light guide layer 4 is grown by laminating ₀₂ N. Here, the growth of Ga _0.98 In _0.02 N is performed after the temperature in the reactor is lowered to about 800 ° C. and the carrier gas is changed from hydrogen to nitrogen. Further, during the growth of In _0.02 Ga _0.98 N, trimethylindium (TMI) and TMG are supplied to the group III raw material.

Thereafter, on the n-side light guide layer 4, three strained quantum wells made of Ga _0.9 In _0.1 N having a thickness of about 3 nm and Ga _0.98 In ₀ having a thickness of about 7.5 nm are formed. Two barrier layers made of _0.02 N are alternately stacked to grow a multiple quantum well (MQW) active layer 5.

Thereafter, Ga _0.98 In _0.02 N having a thickness of about 35 nm and Al _0.02 Ga _0.98 N having a thickness of about 45 nm are stacked on the MQW active layer 5 to form a p-side first layer. The light guide layer 6 is grown. Here, the growth of Al _0.02 Ga _0.98 N is performed again after raising the temperature in the reactor to about 1000 ° C. and returning the carrier gas from nitrogen to hydrogen.

Thereafter, a p-type impurity diffusion suppression layer 7 made of Al _0.02 Ga _0.92 In _0.06 N having a thickness of about 10 nm is grown on the p-side first light guide layer 6. Subsequently, the p-side second light guide layer 8 made of GaN having a thickness of about 15 nm is grown on the p-type impurity diffusion suppression layer 7.

Thereafter, while supplying Group III source materials TMA and TMG, Group V source material ammonia gas, and p-type dopant biscyclopentadienylmagnesium (Cp ₂ Mg) gas, the p-side second light guide layer 8 An electron blocking layer 9 made of p-type Al _0.16 Ga _0.84 N having a thickness of about 10 nm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ is grown thereon. Subsequently, a p-type cladding layer made of p-type Al _0.05 Ga _0.95 N having a thickness of about 0.5 μm and an Mg impurity concentration of about 1 × 10 ¹⁹ cm ⁻³ on the electron block layer 9. Grow 10 The p-type cladding layer 10 may be composed of Al _0.10 Ga _0.90 N / GaN superlattice (SL).

Thereafter, a p-type contact layer 11 made of p-type GaN having a thickness of about 50 nm and an Mg impurity concentration of about 1 × 10 ²⁰ cm ⁻³ is grown on the p-type cladding layer 10.
Next, the substrate 1 grown up to the p-type contact layer 11 is taken out of the reaction furnace, the surface of the p-type contact layer 11 is washed with an organic solvent, and further cleaned by hydrofluoric acid-based wet etching. Then, an insulating film (not shown) made of silicon dioxide (SiO ₂ ) having a thickness of about 0.1 μm is deposited over the entire surface of the p-type contact layer 11. Thereafter, a resist pattern (not shown) having a predetermined shape corresponding to the shape of the mesa portion is formed on the insulating film by a photolithography method, and wet etching using, for example, a hydrofluoric acid-based aqueous solution is performed using the resist pattern as a mask. Thus, a pattern is formed on the insulating film. Next, dry etching using, for example, chlorine (Cl ₂ ) gas is performed until the n-type contact layer 2 is exposed using the insulating film having a predetermined shape as a mask. By this etching, the upper layer portion of the n-type contact layer 2, the n-type cladding layer 3, the n-side light guide layer 4, the MQW active layer 5, the p-side first light guide layer 6, the p-type impurity diffusion suppression layer 7, and the p-side The second light guide layer 8, the electron block layer 9, the p-type cladding layer 10 and the p-type contact layer 11 are patterned into a mesa shape.

Next, the insulating film used as an etching mask is removed by wet etching using, for example, a hydrofluoric acid aqueous solution. Thereafter, an insulating film (not shown) made of silicon dioxide (SiO ₂ ) having a thickness of about 0.2 μm is deposited on the entire surface of the substrate again using, for example, plasma CVD. Thereafter, a resist pattern (not shown) having a predetermined shape corresponding to the shape of the ridge portion is formed on the insulating film by photolithography, and wet etching using, for example, a hydrofluoric acid-based aqueous solution is performed using the resist pattern as a mask. Thus, a pattern is formed on the insulating film. Next, dry etching using, for example, chlorine (Cl ₂ ) gas is performed to the middle of the p-type cladding layer 10 using the insulating film having a predetermined shape as a mask to form a ridge. The remaining thickness of the p-type cladding layer 10 is determined by the design with respect to the light emission angle and the kink level.

Next, the insulating film used as an etching mask is removed by wet etching using, for example, a hydrofluoric acid aqueous solution. Thereafter, the insulating film 12 made of silicon dioxide (SiO ₂ ) having a thickness of about 0.2 μm is deposited on the entire surface of the substrate again using, for example, plasma CVD. Thereafter, a resist pattern (not shown) having a predetermined shape excluding the n-side electrode formation region is formed on the insulating film 12 by photolithography, and using this resist pattern as a mask, for example, a hydrofluoric acid aqueous solution is used. A pattern is formed on the insulating film 12 by wet etching. Next, a titanium (Ti) film and an aluminum (Al) film are sequentially formed on the entire surface of the substrate with the resist pattern remaining, for example, by vacuum evaporation, and then the resist pattern is formed on the Ti film and It is removed together with the Al film. As a result, an n-side electrode 14 in contact with the n-type contact layer 2 through the opening of the insulating film 12 is formed. Next, the alloy process for making the n side electrode 14 ohmic-contact is performed.

  Next, in the same process, the insulating film 12 above the ridge is removed to expose the p-type contact layer 11, and then the nickel electrically connected to the p-type contact layer 11 in the same manner as the n-side electrode 14. A p-side electrode 13 made of a laminate of (Ni) and gold (Au) is formed.

  Next, although not shown, the resonator structure of the laser element is formed by cleavage or the like, and then end face coating is applied to each end face of the cleaved resonator. Here, the resonator length is, for example, 600 μm, the front-side end surface reflectance is, for example, 10%, and the rear-side end surface reflectance is, for example, 95%.

Thus, a GaN semiconductor laser device having the target structure is formed.
The result of calculating the electric field distribution of the semiconductor laser device will be described with reference to FIG.
Al _0.02 Ga _0.92 In _0.06 N constituting the p-type impurity diffusion suppression layer 7 has a compressive strain of about 0.6%, and constitutes the p-side first light guide layer 6 to form the p-type. Al _0.02 Ga _0.98 N in contact with the impurity diffusion suppression layer 7 has a compressive strain of about 0.05%. Since the compressive strain of the p-type impurity diffusion suppression layer 7 is larger than that of the p-side first light guide layer 6, negative fixed charges are induced at these interfaces. FIG. 2 shows the electric field distribution around the active layer 5, but in this embodiment, a negative electric field of about 3.5 × 10 ⁵ V / cm can be obtained in the region of the p-type impurity diffusion suppression layer 7. , Mg as a p-type impurity can be prevented from diffusing into the active layer. As a result, a highly reliable blue-violet semiconductor laser device can be obtained.

In the present embodiment, the p-side first light guide layer 6 in contact with the p-type impurity diffusion suppression layer 7 is composed of an AlGaN ternary compound, but the composition ratio of each element is arbitrary, and the p-type impurity diffusion suppression layer 7 is If the amount of strain is smaller than that of the constituting crystal, an AlGaInN quaternary compound may be used. Since the quaternary compound can independently control the amount of distortion and the refractive index, the light output characteristics of the laser device and the design freedom of the beam shape can be kept large.
(Embodiment 2)
A second embodiment of the present invention will be described with reference to FIG. 3, FIG. 4, FIG. 5, FIG.

FIG. 3 is a cross-sectional view showing the configuration of the semiconductor laser device according to the second embodiment, and FIG. 4 is a calculation result of the relationship between the electric field strength and the In composition ratio in the p-type impurity diffusion suppression layer made of Ga _1-y In _y N. FIG. 5 is a diagram showing the Mg concentration distribution in the second embodiment, FIG. 6 is a diagram showing the IL characteristics of the semiconductor laser device according to the second embodiment, and FIG. 7 is a semiconductor according to the second embodiment. It is a figure which shows the aging characteristic of a laser apparatus.

First, the configuration of the semiconductor laser device according to the second embodiment of the present invention will be described with reference to FIG.
Except for the p-side first light guide layer 26 and the p-type impurity diffusion suppression layer 27, this embodiment is the same as the first embodiment. Here, the p-side first light guide layer 26 is composed of a laminate of Ga _0.98 In _0.02 N and GaN, the p-type impurity diffusion suppression layer 27 and GaN are adjacent to each other, and the p-type impurity diffusion suppression layer 27 is formed. _Is composed of Ga _0.94 In _0.06 N.

Next, the relationship between the In composition ratio y and the electric field F in the p-type impurity diffusion suppression layer in a structure in which the p-type impurity diffusion suppression layer is composed of Ga _1-y In _y N will be described with reference to FIG.
In FIG. 4, the thickness d of the p-type impurity diffusion suppression layer is also a parameter, but the electric field F becomes almost zero when the In composition ratio y is 0.02, regardless of the film thickness, and the In composition ratio y is It can be seen that the negative electric field tends to increase along with the increase. Therefore, in order to suppress diffusion of p-type impurities, it is desirable that the In composition ratio y is 0.03 or more.

In this embodiment, since the thickness of Ga _0.94 In _0.06 N constituting the p-type impurity diffusion suppression layer 27 is 10 nm, a negative electric field of about 3 × 10 ⁵ V / cm can be obtained.
FIG. 5 shows the results of SIMS analysis of the distribution in the layer thickness direction of Mg added as a p-type impurity in the electron block layer 9, the p-type cladding layer 10, and the like. From the figure, the p-type layer has about 1 ×
It was confirmed that Mg added with 10 ¹⁹ cm ⁻³ rapidly decreased in concentration to 10 ¹⁶ cm ⁻³ in the p-type diffusion suppression layer and did not diffuse further from there. Further, FIG. 6 shows the measurement result of the injection current-light output characteristics at room temperature of the semiconductor laser device, and it was found that the threshold current was a very low value of about 35 mA. Further, FIG. 7 shows the result of investigating the dependency of the operating current Iop on the energization time in a constant light output energization test at 60 ° C. and 100 mW. The increase rate of Iop after 1200 hours is 20% or less, and is stable at a high temperature. It was confirmed to work.

As described above, the p-type impurity diffusion suppression layer is made of Ga _1-y In _y N, and the p-side has a laminated structure of Ga _0.98 In _0.02 N and GaN below the p-type impurity diffusion suppression layer. By providing the first light guide layer, a negative electric field can be obtained, so that it can be configured with a combination of the minimum number of elements. Most easily, stable light can be obtained by suppressing diffusion of p-type impurities into the active layer. A group III nitride semiconductor laser device having output characteristics and, as a result, high reliability can be provided.
(Embodiment 3)
A third embodiment of the present invention will be described with reference to FIGS. 8, 9, 10, and 11. FIG.

  FIG. 8 is a cross-sectional view showing the configuration of the semiconductor laser device according to the third embodiment, FIG. 9 is a diagram showing the dependency of the band gap wavelength of the semiconductor laser device according to the third embodiment on the In composition ratio, and FIG. FIG. 11 is a diagram showing a calculation result of the dependence of the current-voltage characteristics on the number of negative electric field layers when a negative electric field layer is stacked.

First, the configuration of the semiconductor laser device according to the third embodiment will be described with reference to FIG.
Except for the structure of the p-type impurity diffusion suppression layer 37, the second embodiment is the same as the second embodiment. In the present embodiment, the p-type impurity diffusion suppression layer 37 includes a negative electric field layer 37a _{1 made} of Ga _0.94 In _0.06 N having a thickness of about 4 nm and a Ga _0.91 In _0.09 N having a thickness of about 4 nm. negative field layer 37a ₂ and thickness made is constituted by lamination of the intermediate layer 37b made of GaN of about 7 nm. As shown in FIG. 4, the strength of the negative electric field in the Ga _1-y In _y N layer can be increased by increasing the In composition ratio y and decreasing the film thickness. However, when the In composition ratio y is increased, the band gap is reduced, so that the In composition ratio y is limited by a trade-off with laser light absorption. FIG. 9 shows the dependence of the band gap of Ga _1-y In _y N on the In composition ratio y. In the 400 nm band laser device, the band gap of Ga _1-y In _y N approaches the wavelength of the laser beam. If y exceeds 0.06, absorption may become a problem. However, when the film thickness is reduced, the absorption edge increases and the absorption volume decreases due to the quantum effect. Therefore, even if the In composition ratio y is larger than 0.06, the influence of absorption can be reduced. Further, as shown in the present embodiment, the negative electric field layers (37a ₁ , 37a ₂ ) are formed in a double structure through the intermediate layer 37b, so that only the negative electric field layer 37a ₂ located at a position away from the active layer is provided. It is possible to increase the In composition ratio y, and it is easy to increase the negative electric field while suppressing the influence of absorption.

As described above, the p-type impurity diffusion suppression layer has a structure in which the negative electric field layer is laminated via the intermediate layer, thereby increasing the In composition ratio y only in the negative electric field layer 37a ₂ located away from the active layer. Since the negative electric field can be increased while suppressing the influence of absorption, diffusion of p-type impurities into the active layer can be suppressed, and stable light output characteristics are obtained. A group III nitride semiconductor laser device having high reliability can be provided.

  Further, the electric field distribution of the present embodiment is shown in FIG. 10, but a negative electric field approximately twice that of the first embodiment is obtained, and the effect of suppressing the diffusion of p-type impurities can be enhanced. In the present embodiment, an example in which the p-type impurity diffusion suppression layer 37 is configured by two negative electric field layers has been described. However, as the number of layers is increased, the effect of suppressing the diffusion of p-type impurities is increased accordingly.

  However, increasing the number of layers can adversely affect current-voltage characteristics. FIG. 11 shows the results of calculating the current-voltage characteristics using the number of negative electric field layers as a parameter. When the number of layers increases, the rising voltage tends to increase, but it has been confirmed that there is no problem with five layers. Therefore, the number of negative electric field layers constituting the p-type impurity diffusion suppression layer 37 is preferably 5 or less.

Further, in the semiconductor laser device described in the third embodiment, the semiconductor layer the intermediate layer 37b sandwiched between the negative field layer 37a ₁ and 37a ₂ constituting the p-type impurity diffusion suppression layer 37 is not doped with impurities intentionally However, for example, an n-type impurity such as Si may be added. It is known that p-type impurities are difficult to diffuse in a semiconductor layer containing n-type impurities at a concentration higher than that, and a synergistic effect with a negative electric field effect can be expected. Therefore, the effect of suppressing the diffusion of p-type impurities can be enhanced, and a highly reliable blue-violet semiconductor laser can be easily realized.

  The group III nitride semiconductor laser device of the present invention can suppress the diffusion of p-type impurities into the active layer, has a stable light output characteristic, and as a result, a group III nitride semiconductor having high reliability A laser device can be provided, and is useful for a semiconductor laser device using a group III nitride semiconductor.

Sectional drawing which shows the structure of the semiconductor laser apparatus concerning Embodiment 1 The figure which shows the electric field distribution of the semiconductor laser apparatus concerning Embodiment 1. Sectional drawing which shows the structure of the semiconductor laser apparatus concerning Embodiment 2 Graph showing the calculation results of the relationship between the electric field strength and the In composition ratio of the p-type impurity diffusion suppression layer composed of Ga _{1-y In y N} The figure which shows Mg concentration distribution in Embodiment 2 The figure which shows the IL characteristic of the semiconductor laser apparatus concerning Embodiment 2 The figure which shows the aging characteristic of the semiconductor laser apparatus concerning Embodiment 2 Sectional drawing which shows the structure of the semiconductor laser apparatus concerning Embodiment 3 The figure which shows In composition ratio dependence of the band gap wavelength of the semiconductor laser apparatus concerning Embodiment 3 Electric field distribution diagram of semiconductor laser device according to Embodiment 3 The figure which shows the calculation result of the negative electric field layer number dependence of the current-voltage characteristic when a negative electric field layer is laminated Sectional view showing the structure of a conventional group III nitride semiconductor laser device

Explanation of symbols

Reference Signs List 1 substrate 2 n-type contact layer 3 n-type cladding layer 4 n-side light guide layer 5 active layer 6 p-side first light guide layer 7 p-type impurity diffusion suppression layer 8 p-side second light guide layer 9 electron blocking layer 10 p P-type contact layer 12 insulating film 13 p-side electrode 14 n-side electrode 26 p-side first light guide layer 27 p-type impurity diffusion suppression layer 37 p-type impurity diffusion suppression layer 37a ₁ negative electric field layer 37a ₂ negative electric field Layer 37b intermediate layer 101 sapphire substrate 102 n-type contact layer 103 n-type cladding layer 104 n-side light guide layer 105 active layer 106 p-side light guide layer 108 p-side first cladding layer 109 electron blocking layer 110 p-side second cladding layer 111 p-type contact layer 112 insulating film 113 p-side electrode 114 n-side electrode

Claims (8)

  A group III nitride semiconductor laser device comprising a p-type impurity diffusion suppression layer having an electric field directed from the p-type cladding layer toward the active layer at least in an equilibrium state between the active layer and the p-type cladding layer. an n-type group III nitride semiconductor region provided with an n-side electrode;
a p-type group III nitride semiconductor region having a p-side electrode and a cladding layer;
An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region;
A p-type impurity diffusion suppression layer composed of Al _x1 Ga _1-x1-y1 In _y1 N (x1 + y1 ≦ 1) is provided between the active layer and the p-type group III nitride semiconductor region. Group III nitride semiconductor laser device. an n-type group III nitride semiconductor region provided with an n-side electrode;
a p-type group III nitride semiconductor region having a p-side electrode and a cladding layer;
An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region;
A first p-type impurity diffusion suppression layer composed of Al _x1 Ga _1-x1-y1 In _y1 N (x1 + y1 ≦ 1) between the active layer and the p-type group III nitride semiconductor region;
Having a _{Al x2 Ga 1-x2-y2} In y2 N (x2 + y2 ≦ 1) second p-type impurity diffusion suppression layer composed between the active layer and the first p-type impurity diffusion suppression layer A group III nitride semiconductor laser device characterized by the above. an n-type group III nitride semiconductor region provided with an n-side electrode;
a p-type group III nitride semiconductor region having a p-side electrode and a cladding layer;
An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region;
A p-type impurity diffusion suppression layer composed of Ga _1-y1 In _y1 N (0 <y1 ≦ 1) between the active layer and the p-type group III nitride semiconductor region; A group III nitride semiconductor laser device, wherein a region adjacent to the p-type impurity diffusion suppression layer in the nitride semiconductor region is a GaN layer. an n-type group III nitride semiconductor region provided with an n-side electrode;
a p-type group III nitride semiconductor region having a p-side electrode and a cladding layer;
An active layer formed of an n-type group III nitride semiconductor between the n-type group III nitride semiconductor region and the p-type group III nitride semiconductor region;
A plurality of layers of Al _xan1 Ga _1-xan1-yan1 In _yan1 N (layers n1 = 1, 2,..., M1, xan1 + yan1 ≦ 1) are formed between the active layer and the p-type group III nitride semiconductor region. A first p-type impurity diffusion suppression layer to be formed;
And a _{Al x2 Ga 1-x2-y2} In y2 N (x2 + y2 ≦ 1) second p-type impurity diffusion suppression layer composed between the active layer and the first p-type impurity diffusion suppression layer The group III nitride semiconductor laser device, wherein the strain amount of the second p-type impurity diffusion suppression layer does not exceed the strain amount of the first p-type impurity diffusion suppression layer.   6. The group III nitride semiconductor laser device according to claim 5, wherein an In composition ratio of the first p-type impurity diffusion suppression layer is larger than an In composition ratio of the second p-type impurity diffusion suppression layer. .   7. The group III nitride semiconductor laser device according to claim 5, wherein the number m of layers is 5 or less.   The group III nitride semiconductor laser device according to claim 5, wherein an n-type impurity is added to at least a part of the second p-type impurity diffusion suppression layer. .

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