JP3699753B2 - Semiconductor laser device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a semiconductor laser device used in an optical disk storage / reproduction device, a laser beam printer, and the like.
[0002]
[Prior art]
In a visible light semiconductor laser using an existing AlGaInP-based material, the forbidden band width difference between the active layer quantum well and the cladding layer is about 450 meV, which is allocated to the conduction band and the valence band. The band discontinuity at is as small as about 200 meV. Furthermore, when the forbidden band width of the active layer quantum well is increased to shorten the oscillation wavelength, the amount of band discontinuity is further reduced, and carriers, particularly electrons, tend to leak from the active layer to the cladding layer. For this reason, as the operating temperature increases, the oscillation characteristics of the laser deteriorate, and the upper limit environmental temperature decreases as the wavelength becomes shorter.
[0003]
In order to overcome this weak point, a superlattice layer such as AlInP / GaInP (for example, Kishino et al., Appl. Phys. Lett. 58, 1822 (1991)) or Al _x In _1-x containing tensile strain is formed outside the active layer. Means such as providing a P single-layer barrier layer (for example, Gase et al., 1994 Autumn Applied Physics Society 20p-S-8) in the p-cladding layer have been attempted. However, the superlattice layer has many different crystal interfaces and causes crystal defects, and it is necessary to manufacture a layer of about 1 nm accurately and uniformly over several cycles, and individual differences in laser elements are likely to occur. Many laser devices designed to shorten the oscillation wavelength have tensile strain in the active layer quantum well. In this case, if an Al _x In _1-x P single-layer barrier layer with tensile strain is introduced, The amount of strain introduced increases as a whole, and crystal defects tend to occur. Further, when x is increased, AlInP also becomes a large barrier against holes, hindering hole injection and increasing the element resistance. These problems exist in the prior art.
[0004]
[Problems to be solved by the invention]
In visible semiconductor lasers using AlGaInP-based materials, in order to increase the allowable operating temperature, the amount of leakage of electrons from the active layer should be reduced, and at that time, the barrier against holes should be made as small as possible to increase device resistance. It is a problem to prevent. There are two types of electron leakage: X-barre and Γ-barre, and it is necessary to take measures to prevent electron leakage for both. Furthermore, in order to improve device characteristics such as device resistance reduction, it is necessary to reduce the Al composition of the cladding layer.
[0005]
[Means for Solving the Problems]
FIG. 1 shows a band lineup of Al _x In _1-x P and (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P grown on a GaAs substrate. Here, the energy position at the bottom of the conduction band Γ of Al _x In _1-x P is set as a common reference and set to zero. According to this, the band discontinuity of the valence band Γ point disappears near x = 0.47, while the band discontinuity of about 100 meV exists at the conduction band Γ point. As in the example of Al _0.47 In _0.53 P, with respect to the valence band, the barrier height with respect to the cladding layer is 25 meV or less, which is about room temperature energy, and it is positive by introducing a barrier layer for the conduction band. A reduction in hole injection efficiency is prevented from greatly affecting device characteristics. For this reason, it is composed of an AlGaInP crystal having an energy gap of Γ point equivalent to (Al _y Ga _1-y ) _0.5 In _0.5 P with compressive strain and Al composition y between 0.8 and 0.95. By introducing a barrier layer, the above conditions can be satisfied. However, the barrier layer cannot form a barrier against the conduction band X point. Accordingly, the band discontinuity with the cladding layer can be increased by lowering the X point position of the barrier layer constituting the quantum well active layer. Specifically, in an AlGaInP-based crystal having a large Al composition ratio and compressive strain, the position of the X point can be lowered by making the Γ-point forbidden bandwidth equal to that of an existing barrier layer. Therefore, an AlGaInP crystal having an Γ point energy gap equivalent to (Al _y Ga _1-y ) _0.5 In _0.5 P with an Al composition y between 0.4 and 0.55 and containing compressive strain is activated. By using it for the barrier layer constituting the layer quantum well, the band discontinuity with the cladding layer at the point X can be increased.
[0006]
Also, since the carrier confinement efficiency is improved by providing a barrier layer such as Al _x In _1-x P in the vicinity of the active layer, the Al composition of the (Al _y Ga _1-y ) _0.5 In _0.5 P cladding layer on the outside is improved. The p-type impurity concentration of the p-cladding layer can be increased and the crystallinity can be improved.
[0007]
In addition, what added As etc. in the range which does not have trouble in this AlGaInP-type crystal | crystallization described in the claim is also contained in the scope of the present invention.
[0008]
[Action]
A barrier layer made of an AlGaInP-based crystal having an energy gap of Γ point equivalent to (Al _y Ga _1-y ) _0.5 In _0.5 P with compressive strain and Al composition y between 0.8 and 0.95 By introducing the barrier, the barrier of the valence band can be almost eliminated while keeping the barrier of the conduction band Γ point as high as 100 eV. An example of this band lineup is shown in FIG. As a result, the high-temperature operating characteristics of the laser element can be improved.
[0009]
As shown in FIG. 3, the barrier layer constituting the active layer quantum well has an Al composition y between 0.4 and 0.55 and a Γ point equivalent to (Al _y Ga _1-y ) _0.5 In _0.5 P. By using an AlGaInP-based crystal (for example, Al _x In _1-x P (0.34 ≦ x ≦ 0.40)) having an energy gap and applied with compressive strain, a band at the X point with the cladding layer The amount of discontinuity can be increased, electron leakage from point X is reduced, and the high-temperature operating characteristics of the laser element are improved.
[0010]
An Al _x In _1-x P barrier layer is provided in the vicinity of the active layer, and the Al composition of the outer (Al _y Ga _1-y ) _0.5 In _0.5 P clad layer is reduced so that y <0.6. It is possible to reduce the oxygen concentration and the growth supply density, and when used for the p-type cladding layer, the p-type impurity concentration can be made higher than before. If this structure is introduced into the n-type cladding layer, the amount of band discontinuity with GaAs can be reduced. These improvements can reduce the element resistance and improve the element characteristics such as the operating temperature rise and the oscillation threshold reduction.
[0011]
【Example】
(Example 1)
This will be described with reference to FIG. n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer (1 × 10 ¹⁸ / cm ³ ) _doped with Si on an n-GaAs (100) substrate (1 × 10 ¹⁸ / cm ³ ) by an organic metal epitaxial growth method. ) 1.5 μm, not doped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P / GaInP / (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P single quantum well, not doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer 15 nm, Zn doped p-Al _0.47 In _0.53 P 20 nm, Zn doped p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer (8 × 10 ¹⁷ / cm ³ ) ([p] = 2 × 10 ¹⁷ / cm ³ ) is grown by 1 μm. The growth temperature is 700 ° C. and the growth pressure is 100 torr. This is mesa-etched and Si-doped n-GaAs (1 × 10 ¹⁹ / cm ³ ) is buried in a thickness of 0.7 μm, and Zn-doped p-GaAs (1 × 10 ¹⁹ / cm ³ ) is grown. Grows 2 μm. Thereafter, p-type and n-type ohmic electrodes are attached and cleaved to form a laser chip. In this device, the maximum oscillation temperature rises by 20 ° C. compared to a device having the same multilayer structure except that there is no AlInP barrier layer. In addition, the element resistance hardly changes.
[0012]
(Example 2)
In addition to the AlInP barrier layer shown in Example 1, an Al _0.4 In _0.6 P crystal is used as the barrier layer instead of (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P constituting the quantum well active layer (FIG. 3). In this case, with respect to X-barrel, the band discontinuity between AlInP and (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P in the active layer can be increased, and the maximum oscillation temperature can be further increased by 5 ° C. compared to the first embodiment. In addition, the oscillation threshold also decreased by 10%.
[0013]
(Example 3)
As shown in FIG. 5, n-Al _0.50 In _0.50 P (10 nm) in which n- (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P is 1.4 μm and Si is doped on the same n-GaAs substrate as in Example 1. ) / N- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (10 nm) (1 × 10 ¹⁸ / cm ³ ) is grown in five layers. After growing (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P directly on the active layer, Zn- _doped p-Al _0.47 In _0.53 P (10 nm) / p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (10 nm) (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P (1 × 10 ¹⁸ / cm ³ ) doped with Zn and grown by 0.9 μm. By adopting this structure, the element resistance and the oscillation threshold were lowered.
[0014]
【The invention's effect】
The element characteristics of a visible light emitting semiconductor laser during high temperature operation are improved, and a semiconductor laser device that can withstand use at a higher temperature than before can be supplied.
[Brief description of the drawings]
1 is a band lineup of Al _x In _1-x P / (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P heterogeneous crystal junctions.
FIG. 2 shows a band lineup by introducing a compressive strained AlGaInP barrier layer in the cladding layer.
FIG. 3 shows a band lineup by introducing a compressive strained AlGaInP barrier layer in the active layer.
FIG. 4 is a cross-sectional view of a laser device in which a compressive strain AlGaInP barrier layer according to the present invention is introduced into a cladding layer.
FIG. 5 is a cross-sectional view of a laser device in which the Al composition of the cladding layer AlGaInP according to the present invention is reduced.
[Explanation of symbols]
_{1 ... p- (Al 0.7 Ga 0.3} ) 0.5 In 0.5 P, 2 ... p-Al 0.47 In 0.53 P, 3 ... u- (Al 0.5 Ga 0.5) 0.5 In 0.5 P, 4 ... n- (Al 0.7 Ga 0.3) _0.5 In _0.5 P, 5 ... u-GaInP, 6 ... u-Al _0.4 In _0.6 P, 7 ... p-type electrode, 8 ... p-GaAs, 9 ... n-GaAs, 10 ... n-GaAs, 11 ... n-GaAs Substrate, 12 ... n-type electrode, 13 ... p- (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P, 14 ... p-Al _0.40 In _0.60 P (10 nm) / (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (10 nm) 5 Period: 15 ... n-Al _0.40 In _0.60 P (10 nm) / (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (10 nm) 5 periods, 16 ... n- (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P.

Claims (1)

In a visible light emitting semiconductor laser device, the Al composition x has an energy gap of Γ point equivalent to (Al _x Ga _1-x ) _0.5 In _0.5 P between 0.8 and 0.95, and compressive strain is low. A first barrier layer composed of added Al _y In _1-y P mixed crystal (y is in the range of 0.44 to 0.50) and whose energy position at the bottom of its conduction band is higher than that of the adjacent cladding layer In the cladding layer near the active layer,
The second barrier layer constituting part of the quantum well active layer made of AlGaInP-based crystal is made of Al _z In _1-z P mixed crystal, and the Al composition z is in the range of 0.35 to 0.40. A semiconductor laser device.

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