JP2001244575A - Semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a semiconductor light emitting element such as a red semiconductor laser element and a light emitting diode wherein the threshold current value is reduced, the high characteristic temperature is ensured and high output and stable operation are obtained in a wavelength band of 630-660 nm. SOLUTION: In a semiconductor light emitting element which has optical guide layers 5, 7 and clad layers 4, 8 above and below an active layer 6 and is composed of AlGaInP based material or AlGaInAsP based material wherein lattice constants of the clad layers and the optical guide layers become a value between lattice constants of GaAs and GaP, the clad layers 4, 8 and the optical guide layers 5, 7 have indirect transition region compositions. One or both of the optical guide layers 5, 7 are doped with impurities to have the same conductivity type (N-type or P-type) as the adjacent clad layers 4, 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device applied to an optical recording / reading light source, an optical writing light source, a light emitting display, and the like.

[0002]

2. Description of the Related Art AlGaInP-based semiconductor materials have attracted attention as red laser materials having an emission wavelength of 635 to 670 nm. In recent years, in particular, there is great expectation as a light source for high-density optical disks. For example, in the document `` Appl.Phys.Lett.,
vol. 63, No. 11, 1486, 1993, watanabe et al '' contains Al
634 nm laser oscillation by a GaInP-based material has been reported. This light emitting element uses p-doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and n-doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P for the upper and lower cladding layers, respectively, and the active region between the cladding layers is Ga _0.65 In _0.35. P / (Al _0.5 Ga
_0.5 ) _{0.5 In0.5} P has a multiple quantum well structure, and an undoped (Al _0.5
Ga _0.5) is constituted by _0.5 an In _0.5 P optical guide layer (separate confinement heterostructure provided carrier confinement layer) (SCH structure).

In AlGaInP, the refractive index and band gap energy are adjusted by the Al composition, and a light confinement layer of an oscillation wavelength order is provided separately from the carrier confinement layer to increase the light intensity in the active region and reduce the oscillation threshold current. are doing. However, in the double hetero structure of the AlGaInP-based material, the band gap energy difference between the active layer and the cladding layer is not sufficient, and the band offset ratio of the heterojunction on the conduction band side is not sufficient. In addition, there is a problem that electrons easily overflow into the cladding layer.

Some of the electrons that have overflowed from the active layer are confined in the cladding layer and distributed to the light guide layer, and the rest leaks out to the cladding layer. The electron leakage naturally increases the threshold current of the device, but the electrons that overflow into the optical guide layer also have a large effect on the device characteristics. In a state where electrons overflow into the light guide layer, the amount of injected electrons for raising the pseudo-Fermi level to a value required for laser oscillation, that is, the threshold current increases. Furthermore, the fact that electrons distributed in the light guide layer disappear due to non-radiative recombination also causes an increase in threshold current. Such an increase in the oscillation threshold current ultimately adversely affects various characteristics such as the device characteristic temperature and high output.

SCH using conventional AlGaInP-based material
In the structure, it is necessary to use AlGaInP having an Al composition smaller than that of the cladding layer as a light guide layer in order to create a refractive index difference necessary for light confinement. The combination of the composition of the cladding layer and the composition of the light guide layer is, as shown in FIG. 2, the intersection of the 帯 point and the X point of the conduction band (Al _0.7 Ga _0.3 ) _0.5 In _0.5 from the relationship between the increase in the Al composition and the luminous efficiency. (Al _0.5 Ga _0.5 ) _0.5 I in the direct transition region with P as the cladding layer
In many cases, n _0.5 P is used as the light guide layer. In the region where the Al composition is smaller than the crossing point of the band, the amount of change in the band gap energy with respect to the Al composition is large. Thus, carriers easily overflow from the active layer to the light guide layer.

The overflow of carriers into the light guide layer can be reduced by setting the light guide layer to have a wide gap. For example, if AlGaInP in the indirect transition region corresponding to the Al composition of 0.73 or more in FIG. 2 is used for the cladding layer and the light guide layer, the band gap energy change with respect to the Al composition change becomes small, and the overflow of carriers can be reduced. Can be. However, in the composition lattice-matched to the GaAs substrate as shown in FIG. 2, the Al composition of AlGaInP serving as an indirect transition region is large, which is not desirable from the viewpoint of the luminous efficiency of the device.

In Japanese Patent Application Laid-Open No. 5-41560,
The lattice constants formed on a GaAs substrate are GaAs and GaP.
A light emitting device having an AlGaInP double heterostructure having a value between the lattice constants of the above is disclosed as a technique relating to a laser having a wavelength shorter than 600 nm. In this prior art, by setting the lattice constant of the light emitting element to a value between the lattice constants of GaAs and GaP, the band gap energy of AlGaInP increases, and light emission of a short wavelength can be obtained. In addition, there are the following advantages with respect to the fabrication of the SCH structure having the above band gap configuration.

FIG. 3 shows an example of -1 from GaAs.
FIG. 3 is a schematic diagram showing band gap energies corresponding to Γ points and X points of a conduction band of AlGaInP in an unstrained state having% lattice mismatch. The broken line in the drawing indicates the band gap energy corresponding to the point 、, and the solid line indicates the band gap energy corresponding to the point X. In the composition of this lattice constant, there is an intersection of the point X and the point Γ where the Al composition is about 0.23.
The composition is an indirect transition type semiconductor. Further, a change in band gap energy with respect to a change in Al composition after becoming an indirect transition semiconductor is small.

As described above, when the lattice constants of the cladding layer and the light guide layer are smaller than GaAs, the Al composition at the intersection of the Γ point and the X point becomes smaller, and is smaller than that in the case where the lattice matching with GaAs is performed. In the Al composition region, the band gap energies of the substantially clad layer and the optical guide layer are equal to each other.
A CH structure is obtained, and there are advantages in luminous efficiency and reliability. However, in reality, the potential barrier for carriers is not simply determined by the band gap energy alone, but also depends on the doping level between heterojunctions. Therefore, in order to improve the carrier confinement efficiency and the like, it is necessary to manufacture an element in consideration of this.

[0010]

SUMMARY OF THE INVENTION The above-mentioned JP-A-5-41
The semiconductor light emitting device described in Japanese Patent No. 560 has an emission wavelength of 60.
This is a technique disclosed for shortening the wavelength to 0 nm or less, and is not designed in consideration of the above-described problem relating to a red laser having an emission wavelength of 630 to 660 nm. Accordingly, an object of the present invention is to provide a semiconductor light emitting device such as a red semiconductor laser device and a light emitting diode which have a high characteristic temperature with a reduced threshold current value, have a high output in a wavelength band of 630 to 660 nm, and operate stably. I do.

[0011]

As a means for achieving the above object, the present invention has a light guide layer and a clad layer above and below an active layer, and the lattice constant of the clad layer and the light guide layer is GaAs. Between Al and the lattice constant of GaP
In a semiconductor light emitting device composed of a GaInP-based material or an AlGaInAsP-based material, the cladding layer and the light guide layer have an indirect transition region composition, and one or both of the light guide layers have the same conductivity type as an adjacent clad layer. It is configured to be doped with impurities.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure, operation and operation of the present invention will be described below in detail with reference to the drawings. The semiconductor light-emitting device of the present invention, for example, a semiconductor laser device, has an AlGaInP-based material or AlGaIn in an indirect transition region where the lattice constant takes a value between the lattice constants of GaAs and GaP.
The cladding layer and the light guide layer are made of AsP, and the light guide layer is formed by doping impurities with the same conductivity type (conductivity type) as the adjacent cladding layer. That is, the present invention relates to an AlGaInP-based material or AlGaInA
In a light emitting device made of an sP-based material, the lattice constant of the cladding layer takes a value between the lattice constants of GaAs and GaP, and the composition of the cladding layer and the light guide layer is different from the SCH structure in the indirect transition region. In addition, the light guide layer is doped to the same conductivity type as the adjacent cladding layer to improve the carrier confinement efficiency and the injection efficiency in the active layer.

In order to form a light confinement structure by the SCH structure, the cladding layer side needs to be made of AlGaIn (As) P having a large Al composition (small refractive index). FIG.
Shows an outline of the band edge energies of AlInP and GaInP.
The smaller the composition, the higher the conduction band energy. Therefore, the undoped AlGaInP light guide layer and the n-Al
An outline of the band energy of the hetero junction composed of the GaInP clad layer is as shown in FIG. That is, the light guide layer hinders electron injection into the active layer. Further, during operation of the device, although the height of the potential barrier due to the conduction band of the light guide layer is lower than the thermal equilibrium state of FIG. 5A, it still causes the injection of electrons into the active layer. .

When the electron density is increased by n-type doping of the light guide layer as in the present invention, the diffusion potential generated at the heterojunction between the clad layer and the light guide layer is reduced, and the conduction band of the light guide layer becomes n-clad. As it approaches the layer conduction band, the potential barrier for electrons decreases. FIG. 5B shows an outline of the band energy in a thermal equilibrium state when the light guide layer is doped with impurities. In this case, the conduction band energies of the light guide layer and the cladding layer are substantially the same, and the width of the depletion layer is reduced due to an increase in the impurity concentration of the light guide layer. As shown in the figure, spike-like and notch-like potential barriers are formed at the hetero interface due to band discontinuity. As a result, tunneling and heat release are facilitated, and electron injection efficiency is greatly improved. On the valence band side, the potential barrier for holes is relatively high, and the hole confinement efficiency is improved.

Next, the band energy near the p-type cladding layer and the light guide layer will be described. FIG. 6A shows an outline of the band energy in a thermal equilibrium state when the light guide layer is undoped. When the p-type impurity concentration is low, since the conduction band energy of the light guide layer is lower than that of the clad layer, electrons easily overflow from the active layer to the light guide layer. This is better in forward-biased operation of the device, but still not sufficient in terms of electron confinement. When the light guide layer is doped with p-type, the valence band of the light guide layer approaches the valence band of the p-cladding layer and the energy on the conduction band side, that is, the active layer, as shown in the schematic diagram of FIG. The potential barrier of the electrons as viewed from above increases. This improves the efficiency of confining electrons in the active layer.

In the case of undoping, there is a band discontinuity as shown in FIG. 6A, and a spike-like potential barrier formed between the cladding layer and the light guide layer is high and wide. These lower the hole injection efficiency. The effective mass of a valence band hole is heavier than the effective mass of a conduction band electron. Therefore, there is a problem that holes do not easily overflow from the active layer but are difficult to inject. It is also susceptible to potential spikes formed at the heterointerface, which are of little concern for electrons.

When the light guide layer is doped with p-type, the valence band of the light guide layer approaches the valence band of the p clad layer as shown in the schematic diagram of FIG. The width becomes narrow. This facilitates heat release and tunneling of holes and improves injection efficiency. As described above, the hole injection efficiency and the electron confinement efficiency are improved, and the threshold current is reduced. In the above description, AlGaInP has been described as an example. However, AlG containing As as a composition of the cladding layer and the light guide layer is described.
The same applies to aInAsP. Further, the light guide layer may have a strain with respect to the cladding layer.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the semiconductor light emitting device of the present invention will be described below with reference to a semiconductor laser device having a ridge stripe structure. FIG. 1 is a view showing one embodiment of the semiconductor light emitting device of the present invention, and is a sectional view schematically showing the structure of a semiconductor laser device. The semiconductor laser device shown in FIG. 1 uses, for example, an n-GaAs substrate 1 as a substrate, and n-GaAs _0.7 P _0.3 for eliminating lattice irregularity between the substrate 1 and an element portion.
An element portion is formed via the lattice relaxation buffer layer 2 and the n-Ga _0.66 In _0.34 P buffer layer 3, and the element portion is sequentially stacked on the n-Ga _0.66 In _0.34 P buffer layer 3. An n- (Al _a1 Ga _1-a1 ) _b1 In _1-b1 P cladding layer 4 whose lattice constant takes a value between the lattice constants of GaAs and GaP;
(0.51 <b1 <1: In this embodiment, a1 = 0.4,
b1 = 0.66), n- (Al _a2 Ga _1-a2 ) _b2 In _1-b2 P light guide layer 5, (a
2 <a1: a2 = 0.23, b2 = 0.6 in this embodiment
6), undoped GaInAsP active layer 6, p- (Al _a2 Ga _1-a2 ) _b2 In _1-b2 P light guide layer 7, (a
2 <a1: a2 = 0.23, b2 = 0.6 in this embodiment
6), p- (Al _a1 Ga _1-a1 ) _b1 In _1-b1 P clad layer 8,
(0.51 <b1 <1: In this embodiment, a1 = 0.4,
b1 = 0.66), SiO ₂ insulating film 9, p- _{Gab3In1 -b3P} intermediate layer 10 (b3 =
0.66), and a p-GaAs _b4 P _{1 -b4} contact layer 11 (b4 = 0.70 in the present embodiment). A p-side electrode 12 and an n-side electrode 13 are provided.

In this embodiment, the lattice constants of the cladding layers 4 and 8 and the light guide layers 5 and 7 are-
The lattice irregularity is 1.0%. Since GaInP having the above-mentioned lattice constant has a shorter wavelength than 600 nm, the active layer 6 is adjusted to emit red light by using GaInAsP or the like.

The device of this embodiment was manufactured by metal organic chemical vapor deposition (MOCVD). At this time, TMG, TMA, and TMI are used as group III organic metal materials, and PH ₃ and AsH ₃ are used as group V materials. p
The mold cladding layer 8 and the light guide layer 7 are made of, for example, DMZn.
Is doped with an impurity at a concentration of 5 to 7 × 10 ¹⁷ cm ⁻³ . Further, the growth method, the raw material, and the impurity dopant are not limited thereto, and may be other materials. Also, a lattice buffer layer 2 for eliminating lattice irregularities
As a material of GaAsP, GaInP or the like can be used in addition to GaAsP. Further, as the semiconductor substrate 1, Ga
In addition to As, a GaP substrate or the like may be used.
An element portion may be formed on an AsP substrate.

In the fabrication of the device of this embodiment, the growth conditions for the lattice buffer layer 2 were optimized, and the device surface was sufficiently flat, and the crystallinity and luminous efficiency were good. FIG.
The oscillation wavelength of the semiconductor laser device having the structure shown in FIG.
m. When the characteristics of this device were evaluated, the threshold current was lower than that of the conventional device, and the characteristic temperature was higher.

[0022]

As described above, according to the present invention, the light guide layer and the cladding layer are provided above and below the active layer, and the cladding layer and the light guiding layer have lattice constants between GaAs and GaP. AlGaInP-based material or Al
In a semiconductor light emitting device composed of a GaInAsP-based material, the cladding layer and the optical guide layer have an indirect transition region composition, and one or both of the optical guide layers are doped with impurities of the same conductivity type as the adjacent cladding layer. Configuration. That is, by performing n-type impurity doping on the light guide layer on the n-type cladding layer side, the potential barrier at the time of electron injection can be reduced, thereby improving electron injection efficiency and hole confinement efficiency. did. Therefore, the threshold current value was dramatically reduced. Further, by doping the light guide layer on the p-type clad layer side with p-type impurities, the conduction band energy of the p-type light guide layer can be increased, and the efficiency of confining electrons in the active layer is improved. Non-radiative recombination due to electrons spilling over the mold light guide layer was reduced. In addition, the spike-like potential barrier that hinders hole injection was also reduced. As a result, the oscillation threshold current of the device has been dramatically reduced. Also,
The characteristic temperature of the device was also high. In addition, by selecting the lattice constants of the cladding layer and the light guide layer to be smaller than the lattice constant of GaAs, AlGaIn which is an indirect transition is obtained.
The Al composition of P or AlGaInAsP could be reduced. As a result, the Al content in forming the device was small, the device deterioration such as end face oxidation was reduced, and the deterioration over time such as an increase in threshold current was small. From the above, AlG
The effect of improving the characteristics of a red light-emitting element composed of an aInP-based material or an AlGaInAsP-based material and having a lattice constant between GaAs and GaP was obtained.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a semiconductor light emitting device of the present invention, and is a cross-sectional view schematically showing a structure of a semiconductor laser device.

FIG. 2 shows AlGaInP having the same lattice constant as GaAs.
A of band gap energy corresponding to point X and point Γ
It is a figure which shows the change by 1 composition.

FIG. 3 shows AlGa having a lattice constant of -1% from GaAs.
It is a figure which shows the change by the Al composition of the band gap energy corresponding to the X point and the Γ point of InP.

FIG. 4 is a diagram showing a change in band gap energy of AlInP and GaInP depending on a lattice constant.

5A is a diagram showing an outline of band energies of an undoped optical guide layer and an n-type clad layer in a thermal equilibrium state, and FIG. 5B is a diagram showing bands of an n-type optical guide layer and an n-type clad layer in a thermal equilibrium state. It is a figure showing the outline of energy.

FIG. 6A is a diagram showing an outline of band energies of an undoped optical guide layer and a p-type clad layer in a thermal equilibrium state, and FIG. 6B is a diagram showing bands of a p-type optical guide layer and a p-type clad layer in a thermal equilibrium state. It is a figure showing the outline of energy.

[Explanation of symbols]

1: n-GaAs substrate 2: n-GaAs _0.7 P _0.3 lattice buffer layer 3: n-Ga _0.66 In _0.34 P buffer layer 4: n- (Al _a1 Ga _1-a1 ) _b1 In _1-b1 P cladding layer 5 : N- (Al _a2 Ga _{1 -a 2} ) _b2 In _{1 -b 2} P light guide layer 6: undoped GaInAsP active layer 7: p- (Al _a2 Ga _{1 -a 2} ) _b2 In _{1 -b 2} P light guide layer 8: p _{- (Al a1 Ga 1-a1} ) b1 In 1-b1 P cladding layer 9: SiO ₂ insulating film _{10: p-Ga b3 In 1} -b3 P intermediate layer _{10 11: p-GaAs b4 P} 1-b4 contact layer 12 : P-side electrode 13: n-side electrode

Claims (1)

[Claims] An optical guiding layer and a cladding layer are provided above and below an active layer, and the cladding layer and the optical guiding layer have a lattice constant of GaAs.
In a semiconductor light emitting device composed of an AlGaInP-based material or an AlGaInAsP-based material having a value between s and a lattice constant of GaP, the cladding layer and the light guide layer have an indirect transition region composition, and one of the light guide layers or A semiconductor light emitting device wherein both are doped with impurities of the same conductivity type as an adjacent cladding layer.