JPH104239A - Semiconductor light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode having a ridge structure which can be manufactured in simple steps. SOLUTION: Within a semiconductor laser, a selectively oxidizable p-AlAs semiconductor layer 18 is provided between a ridge structure 19-21 and an active layer 16 so that a selective oxide layer 18b may be formed by oxidizing the semiconductor layer part corresponding to the side edge part of the ridge width in the manufacturing step so as to leave the part corresponding to the center of the ridge width intact as the semiconductor layer part 18A. The transverse mode control and the current constriction are made possible by assembling the selective oxidazed part 18B together with the ridge structure. In such a constitution, the ridge structured semiconductor layer can be manufactured by only a single growing step for simplifying the manufacturing step. Furthermore, the width of the ridge structure is made narrow on the end of the resonator and wide on the central part, so that the effective ridge width in the central part may be narrowed and a current blocking structure is formed near the end. Through these procedures, the laser threshold can be reduced while enabling a circular beam of small diameter to be emitted as well as the laser COD to be avoided.

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, and more particularly, to a structure of an edge emitting semiconductor light emitting device having a double hetero structure.

[0002]

2. Description of the Related Art A semiconductor light emitting device having a double hetero structure has a structure in which an active layer having a small band gap is sandwiched above and below a crystal layer having a larger band gap. In this structure, since the upper and lower crystal layers have a higher refractive index than the active layer, the laser light is preferably confined in the active layer.

FIG. 4 shows a structure of a conventional short wavelength laser of a type called a buried ridge waveguide type semiconductor laser.
FIG. 1A shows an entire cross section, and FIG. 1B shows a partially detailed cross section of FIG. 1A. On the n-GaAs substrate 51,
N- (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P cladding layer 52, n- (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P light confinement layer 53, a plurality of Ga _0.5 In _0.5 P well layers 54 and (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P barrier layer 55 sandwiching the well layer
A quantum well active layer 56 of p- (Al _0.1 Ga
_0.9 ) _0.5 In _0.5 P light confinement layer 57 is formed thereon, and further thereon, a ridge structure of p- (Al _0.3 Ga _0.7 ) _0.5 In
_0.5 P cladding layer _{58, p-Ga 0.5 In 0.5} P layer 59, and, p-GaAs contact layer 60 is formed. A p-side electrode and an n-side electrode (not shown) are arranged so as to sandwich the entirety in the vertical direction. R-structure p- (Al _0.3 Ga _0.7 )
The ridge width of the _0.5 In _0.5 P cladding layer 58 is about 4 μm at the bottom of the ridge, and on both sides in the width direction of the ridge,
An n-GaAs buried layer 61 for current blocking and transverse mode control is formed.

A conventional semiconductor laser of the type described above, for example, in the case of a semiconductor laser oscillating at 680 nm, has an oscillation threshold current of about 30 mA, and an optical output of 50 mW or more can be obtained in the basic transverse mode operation.

[0005]

In the conventional semiconductor laser, in order to form the ridge structure, a growth process up to the p-GaInP layer 59 and n-GaAs burying after forming a ridge waveguide by a photolithography method. A step of growing the layer 61 and a subsequent step of growing the p-GaAs layer 60;
Requires two crystal growth steps. Therefore, there is a problem that the process is complicated and the production efficiency is low.

Further, a radiation beam obtained from a conventional semiconductor laser has an elliptical shape having a divergence of, for example, about 7 ° × 30 °, and the elliptical beam pattern makes it difficult to focus the beam on the hole of the optical disk. There are also problems.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a semiconductor light emitting device having a nearly circular radiation beam pattern whose process is simple and whose beam size can be easily reduced.

[0008]

According to the present invention, there is provided a semiconductor light emitting device comprising an optical resonator having upper and lower active layers sandwiched between crystal layers having a band gap larger than the band gap of the active layer. At least one of the crystal layers has a composition of Al _X Ga _{1 -X} As with 0.8 <x ≦ 1.
Wherein one part of the semiconductor layer is formed on the oxide film layer.

In the semiconductor light emitting device of the present invention, during the manufacturing process, the portion for selectively oxidizing the semiconductor layer to form a selectively oxidized layer and the portion to be left as a semiconductor layer may be selected by selecting the oxidation conditions. I can do it. The selective oxidation layer is
By combining with the ridge structure, current confinement and transverse mode control of the laser can be performed, so that a step of growing a buried layer for burying the ridge structure is not required.

[0010] Further, by matching the positional relationship with the ridge structure, the width left as a semiconductor layer portion is made an effective ridge width, and this ridge width can be selected by selection of oxidation conditions, so that the effective ridge width is reduced. It is possible to reduce the threshold value for laser oscillation by making it smaller, and to form a current blocking structure at the end face of the resonator at the same time.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a particularly preferred embodiment of the semiconductor light emitting device of the present invention, the crystal layer above the active layer has a ridge structure, and the width of the ridge structure is equal to the light intensity at the end face of the optical resonator in the resonator direction. It is formed smaller than the central part of the resonator.
Here, when the semiconductor layer made of Al _X Ga _{1 -X} As (0.8 <x ≦ 1) is selectively oxidized, the ridge width and the oxidation conditions are appropriately selected, so that the ridge is formed at the center of the optical resonator. AlAs is oxidized only at the side edges, and AlAs is oxidized over the entire ridge width at the end face.

Since the selective oxide layer acts as a layer for current confinement and lateral mode control, the effective ridge width can be reduced. On the other hand, near the resonator end face,
Oxidation of AlAs in the entire width direction of the ridge can effectively prevent a current flowing through the cavity end face. Further, since the electric field of the light spreads greatly at the end face of the resonator, a nearly circular output beam pattern is obtained, and the beam diameter can be easily reduced.

In general, in a conventional short-wavelength semiconductor laser, the cavity facet is thermally melted by laser light,
The phenomenon that laser oscillation stops instantaneously "COD
(Catastrophic Optical Damage) "frequently occurs, which shortens the life of the semiconductor laser. This COD is conventionally
This is prevented by adopting a window structure in which the resonator end face is transparent to oscillation light, or an end face non-injection structure in which current is not injected into the end face.

There is a report on selective oxidation of the AlAs layer applied to the formation of a vertical cavity in a surface emitting laser device (Y. Hayashi et al., Electronics Letters, V).
o.31, pp.560-562,1995). In this surface emitting laser device,
The AlAs layer in the peripheral portion is oxidized while leaving the center portion of the cylindrical mesa to reduce the diameter of the effective active region of the cylindrical mesa, thereby reducing the threshold value and the laser diameter.
However, in the present invention, by applying the formation of the selective oxidation layer to a semiconductor laser having a ridge structure, there is obtained an advantage that a growth step for forming a buried layer is not required.

In the present invention, a large COD light output can be obtained by applying the selective oxidation layer to a double hetero structure.
Further, this is also different from the above-mentioned report example in that an effect based on the positional relationship between the selective oxidation region and the ridge region is obtained. Further, in a preferred embodiment of the present invention, by applying selective oxidation of the semiconductor layer to a semiconductor light emitting element having a ridge structure having a small width near an end face, an advantage not obtained in the conventional surface emitting laser device can be obtained. .

The present invention will be described in more detail with reference to the drawings. FIG. 1A is a cross-sectional view showing the structure of a semiconductor laser according to an embodiment of the present invention, and FIG. 1B is a partially detailed cross-sectional view thereof.

On the n-GaAs substrate 11, first, a 1 μm thick n- (Al _0.3 Ga _0.7 ) _0.5 In _0.5
P clad layer 12, 20 nm thick (Al _0.1 Ga _0.9 )
_0.5 In _0.5 P light confinement layer 13, Ga _0.5 In of 7 nm thickness
_0.5 P quantum well layer 14 and 10 nm thick (Al _0.1 Ga
_0.9 ) _0.5 In _0.5 P quantum well active layer 1 composed of P barrier layer 15
6, and 20 nm thick (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P
The light confinement layer 17 is formed by growth.

Further, a semiconductor layer 2 constituting the semiconductor layer is further formed thereon.
A p-AlAs layer 18 having a thickness of 0 nm is laminated, and the widthwise central portion of the optical resonator is left as it is as a p-AlAs layer 18A, and the peripheral portion excluding the central portion is oxidized during the manufacturing process. A selective oxidation layer 18B is formed. Semiconductor layer 1
8, a 1 μm thick p- (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P cladding layer 19 having a ridge structure as a whole,
A 20 nm thick p-Ga _0.5 In _0.5 P layer 20 and 1 μm
A stack of p-GaAs contact layers 21 having a thickness of m is formed. An SiN layer 22 is formed to cover the entire surface including the ridge structure and the semiconductor layer, and further, an electrode (not shown) is formed across the entire surface. The ridge structure has a rod shape elongated in the resonator direction as a whole, and is formed in a tapered shape in which the vicinity of both end surfaces is tapered in the width direction, and a cross section in a direction orthogonal to the resonator direction is trapezoidal. .

The semiconductor laser of the above embodiment was actually manufactured. First, on the n-GaAs substrate 11, n- (Al _0.3
From Ga _{0.7) 0.5} In _0.5 P cladding layer 12, p-GaAs
The layers up to the contact layer 21 were sequentially formed. In this film formation,
The MOCVD method was used, and its raw materials were TMIn and TeGa as Group III materials, and PH ₃ and AsH ₃ as Group V materials.
Was used respectively. As the doping gas, DEZn was used to form the p-type conductivity, and SiH ₄ was used to form the n-type conductivity.

Next, a SiN _x layer was formed on the entire surface, and this was patterned using a usual photolithography technique. As shown in FIG. 2, the pattern has a stripe shape as a whole, and is tapered at both ends of the stripe. Subsequently, p-Al is formed by wet etching using the stripe pattern as a mask.
The wafer having the ridge structure of FIG. 1 was obtained by selectively removing the upper surface of the As layer 18. According to the pattern shown in FIG. 2, the resonator length was 400 μm, the ridge width at the bottom of the ridge was 4 μm at the center in the resonator direction, and 1 μm at both end faces in the resonator direction.

Subsequently, the wafer was set on a quartz bell jar and heated while introducing steam to raise the wafer temperature to 450 °. By maintaining this state for about 30 minutes, the p-AlAs layer 1 disposed below the ridge structure is formed.
8 was oxidized. By selecting appropriate oxidation conditions,
At the center of the cavity of the p-AlAs layer 18 under the ridge, an AlAs semiconductor layer portion 18A having a width of about 3 μm is left as it is at the center of the ridge in the width direction, and a selective oxide layer 18B is formed on the peripheral portion of the ridge in the width direction. Formed. In the vicinity of the end face of the ridge in the resonator direction, the entire AlAs layer 18 in the entire width direction is oxidized to form the selective oxidation layer 18B. By adopting such selective oxidation, 3 μm is formed at the center in the resonator direction.
A current path of the laser having the width of m was obtained. On the other hand, no current path was formed near the cavity facet, and the cavity facet was formed in a current non-injection structure.

Thereafter, the Si constituting the insulating and protective films is formed.
An _Nx layer 22 was formed on the entire surface, and a window for a current path was formed above the ridge. Polishing the n-GaAs substrate 11 from the back surface,
After the thickness of the entire wafer was reduced to about 100 μm, a p-side electrode and an n-side electrode were formed on the upper surface of the stack and the back surface of the substrate, respectively.

The characteristics of the semiconductor laser obtained above were measured. The measured threshold current was 20 mA, and the quantum efficiency was 0.4 W / A. The oscillation wavelength is 680 nm. In this semiconductor laser, COD was not observed in the range of laser output up to 100 mW due to the formation of the current blocking structure on the end face. The full width at half maximum of the far field image was 25 ° in a direction parallel to the bonding surface and 30 ° in a direction perpendicular to the bonding surface. The aspect ratio of the far-field image was 1.2 (30/25), and a nearly circular and favorable beam shape could be realized.

FIGS. 3A and 3B show a semiconductor laser according to a second embodiment of the present invention, similarly to FIGS. 1A and 1B. The semiconductor laser of this embodiment is 0.9
It oscillates at a wavelength of 8 μm.

The semiconductor laser of the present embodiment has the same structure as the semiconductor laser of the above-described embodiment as a whole, and has a material composition and a part of the active layer and the ridge structure which are different from those of the previous embodiment. Different. n-GaAs
On the substrate 23, a 2 μm thick n-Al _0.3 Ga
_0.7 As clad layer 24, 10 nm thick Al _0.1 Ga _0.9 A
s-light confinement layer 25, quantum well active layer 28 consisting of 10 nm thick Ga _0.8 In _0.2 As quantum well layer 26 and 10 nm thick Al _0.1 Ga _0.9 As barrier layer 27, 20 nm thick A
A _0.1 Ga _0.9 As light confinement layer 29 is formed, and a 10 nm-thick p-AlAs layer 30 having a semiconductor layer portion 30A and a selective oxidation layer 30B is further formed thereon. p
On the -AlAs layer 30, p-GaAs contact layer 32 of p-Ga _0. 7Al _0.3 As cladding layer 31 and 1μm thickness of 2μm thickness forming the ridge structure is formed, covering the entire stack including the ridge structure An SiN layer 33 is formed. Other configurations such as the ridge structure are the same as the configurations in the previous embodiment.

In the second embodiment, the same characteristics as those in the previous embodiment were obtained. A device having a resonator length of 800 μm and a reflection film of 5% / 95% applied to the end faces of the resonator, respectively, to provide a threshold current of 15 mA and a quantum efficiency of 1 W / A
Thus, characteristics without COD can be obtained up to a drive current of 1 A.
In the above embodiments, p-AlAs is used as the semiconductor layer for performing selective oxidation.
The composition is not limited to AlAs, but may be any Al _x Ga ₁ -x As having a composition given by x in the range of 0.8 <x ≦ 1. Also,
In the above embodiments, the example of the semiconductor laser formed on the GaAs substrate has been described. However, the semiconductor laser may be formed on the InP substrate. In this case, for example, since the lattice constant of InP and AlAs is different by about 3.7%, the thickness of the AlAs semiconductor layer is preferably set to 10 nm or less.

The present invention is not limited to a laser structure formed by epitaxial growth, but may be applied to a laser structure formed by bonding a wafer formed on a heterogeneous substrate using a bonding technique.

In the semiconductor laser having the ridge structure according to the present invention,
A circular beam shape can be easily obtained, and a semiconductor laser having a large COD light output can be manufactured. That is, a ridge structure in which the effective ridge width differs in the resonator direction can be formed by selecting the oxidation conditions of the semiconductor layer. By obtaining a ridge of any effective width, the necessary current confinement and lateral mode control can be obtained without the need for a step of growing a buried layer.
The threshold current for laser oscillation is reduced, and a current blocking structure is formed on the end face of the resonator. In other words, by reducing the ridge width at the resonator end face, the end face non-injection structure is formed in a so-called self-aligned manner. In addition, the merit that the electric field of the light greatly spreads and a substantially circular and narrow exit beam pattern can be obtained can be realized at the same time.

[0029]

As described above, according to the semiconductor light emitting device of the present invention, by selectively oxidizing the semiconductor layer to form the selective oxide film layer, the structure for controlling the current confinement and the transverse mode can be obtained. Can be obtained, and a semiconductor light emitting device having a ridge structure can be obtained without the need to grow and form a buried layer. Therefore, the present invention has a remarkable effect of simplifying the manufacturing process of the ridge waveguide type semiconductor light emitting device.

[Brief description of the drawings]

FIGS. 1A and 1B are a cross-sectional view showing a structure of a semiconductor laser according to an embodiment of the present invention, and a partially detailed cross-sectional view thereof, respectively.

FIG. 2 is a plan view showing a shape of a mask for forming a ridge.

3A and 3B are a cross-sectional view showing a structure of a semiconductor laser according to another embodiment of the present invention, and a partial detailed cross-sectional view thereof, respectively.

FIGS. 4 (a) and (b) are cross-sectional views showing the structure of a conventional semiconductor laser, similarly to FIGS. 1 (a) and 1 (b).

[Explanation of symbols]

 Reference Signs List 11 n-GaAs substrate 12 n-GaAs cladding layer 13 n- (AlGa) InP light confinement layer 14 GaInP well layer 15 (AlGa) InP barrier layer 16 quantum well active layer 17 p- (AlGa) InP light confinement layer 18 p-AlAs layer 18A semiconductor layer portion 18B selective oxidation layer 19 p- (AlGa) InP clad layer 20 p-GaInP layer 21 p-GaAs contact layer 22 SiNx layer 23 n-GaAs substrate 24 n-AlGaAs clad layer 25nAlG Light confinement layer 26 GaInAs well layer 27 AlGaAs barrier layer 28 Quantum well active layer 29 p-AlGaAs light confinement layer 30 p-AlAs layer 30 A semiconductor layer portion 30 B selective oxidation layer 31 p-GaAlAs cladding layer 32 p-GaAs contact layer 33 SiNx layer 51 n-GaAs substrate 52 n- (AlGa) InP cladding layer 53 n- (AlGa) InP light confinement layer 54 GaInP well layer 55 (AlGa) InP barrier layer 56 Quantum well active layer 57 p- (AlGa) InP light confinement layer 58 p- (AlGa) InP clad layer 59 p-GaInP layer 60 p-GaAs Contact layer 61 n-GaAs embedded layer

Claims (3)

[Claims] 1. A ridge waveguide type semiconductor light emitting device comprising an optical resonator having upper and lower active layers sandwiched by a crystal layer having a band gap larger than the band gap of the active layer, wherein at least one of the crystal layers is .8. A semiconductor light-emitting device comprising: one semiconductor layer having a composition of Al _x Ga _1-x As, wherein x <x ≦ 1, and a part of the semiconductor layer is formed on an oxide film layer. 2. The optical device according to claim 1, wherein the crystal layer on the active layer has a ridge structure, and the width of the ridge structure is smaller in the vicinity of the end face of the optical resonator than in the central portion of the optical resonator.
3. The semiconductor light emitting device according to item 1. 3. The semiconductor layer, wherein substantially all of a portion matching the width of the ridge structure is formed in the oxide film layer near an end face of the optical resonator, and at a central portion of the optical resonator, 3. The semiconductor light emitting device according to claim 2, wherein only a side edge portion of a portion corresponding to a width of the ridge structure is formed in the oxide film layer.