JPH0541559A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a semiconductor laser which has excellent temperature characteristics with a low threshold value by controlling an inductive current of a semiconductor laser. CONSTITUTION:A semiconductor laser of InGaAsP/InP group comprises a current block layer structure having a distorted superlattice structure 15 alternately forming InxGa1-xAs layer where the composition x of In is larger than 0.53 and InP layer on the entire region or a part of the pn junction interface where a clad layer 16 on the substrate side is in contact with the part other than an active layer 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a current blocking layer structure, and more particularly to a semiconductor laser of a hostile type used for subscriber optical transmission.

[0002]

2. Description of the Related Art In a semiconductor laser having a pnpn thyristor type current blocking layer having a conventional structure, a leak current flowing through a gap between the current blocking layer and the active layer poses a problem, leading to an increase in threshold value and deterioration of high temperature characteristics. Was there. This is a homojunction in which the interface with the substrate-side cladding layer is biased in the forward direction with respect to the leakage current flowing through the gap between the block layer and the active layer, so if a voltage above the diffusion potential is applied to this portion. Electric current easily flows. Therefore, these characteristics cannot be improved unless the electric resistance of this portion is increased.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks of the conventional current block structure and realize a semiconductor laser having a low threshold value and excellent high temperature characteristics.

[0004]

The semiconductor laser of the present invention is a semiconductor laser having a current block structure, and a compressive strain is applied to all or part of the pn junction interface where the substrate-side cladding layer and the portion other than the active layer are in contact with each other. It is characterized by having a current block structure having a strained superlattice structure.

InGaAsP having a current block structure
/ In InP-based semiconductor laser, the whole or part of the pn junction interface where the portions other than the substrate-side cladding layer and the active layer in contact with the composition x of In is larger than 0.53 In _x
The above problems can be solved by a current block layer structure having a strained superlattice structure in which Ga _{1 -x} As and InP are alternately laminated.

AlGa having a current block structure
In an As / GaAs semiconductor laser, a structure of a current block layer having a strained superlattice structure in which InGaAs and AlGaAs are alternately laminated on all or part of a pn junction interface where the substrate-side cladding layer and a portion other than the active layer are in contact with each other. The above problems can be solved by the above.

[0007]

The principle of the present invention is that the material is InP / InGaAsP.
A system laser will be described as an example.

In having a composition x of In larger than 0.53
_x Ga _1-x As and has a InP are stacked alternately In _x
It has recently been found that in a Ga _{1 -x} As / InP strained superlattice (compressive strain in this case), band discontinuity (particularly valence band discontinuity) becomes large and carrier injection hardly occurs. _{This, In 0. 5 3 Ga 0} . 4 7 As / In
In the P heterojunction, the energy discontinuity in the valence band is about 30.
Although there is 0 meV, as the composition of In is increased, In
Values of energy discontinuity of up to 520 meV are obtained in As / InP heterojunctions. Such a large energy discontinuity hinders the injection of carriers (holes in this case), resulting in a large electrical resistance.

FIG. 2 is a diagram for explaining the principle of the present invention, and schematically shows this state. Figure 2 (a)
In the conventional structure, when a forward voltage exceeding the diffusion potential is applied to the InP homojunction, electrons and holes are injected over the pn junction, and a current flows. However, in the structure of the present invention shown in FIG. 2B, strain In _x Ga _{1 -x} As / In
Since a P-strained superlattice is included, In _x Ga _{1 -x} As / InP
The flow of carriers can be prevented to some extent at the hetero interface. Therefore, the electric resistance becomes larger than that of the conventional structure, and the leak current can be reduced.

The principle is the same for the AlGaAs / GaAs system and other materials.

[0011]

The present invention will be described below with reference to the drawings. FIG. 1 shows an InGaAsP / InP according to an embodiment of the present invention.
It is a figure which shows the cross section of a semiconductor laser. A partially enlarged view of the strained superlattice structure is also shown. In manufacturing this element, first, an n-InP clad layer 16 having a thickness of about 1 μm and an n-In layer having a thickness of 0.15 μm were formed on an n-InP substrate.
_{0. 7 6 Ga 0. 2} 4 As 0. 5 5 P 0. 4 5 active layer 1
4, p-InP clad layer 12 having a thickness of about 1 μm is sequentially crystal-grown to produce a DH wafer. Then SiO ₂ width 1.5 [mu] m using a mask, processed into a ridge-like height 1.5 [mu] m, an In ₀ of 30 angstroms (A) thick by _{MOVPE. 8} Ga _{0. 2} As17,100A thick InP
After alternately growing 5 layers of 18 to form the strained superlattice layer 15,
Subsequently, 0.8 μm thick p-InP12, 0.7 μm
The thick n-InP 13 is grown sequentially. Si with hydrofluoric acid
After removing the O ₂ mask, a 1 μm thick p-In layer is formed on the O ₂ mask.
P12, 0.5 μm thick p ⁺ -InGaAs11 is grown. Finally, after polishing the substrate to a thickness of about 150 μm, electrodes are formed on the p-side and the n-side. The semiconductor laser having the current block structure of the present invention thus manufactured was cut into a size having a cavity length of 300 μm, mounted on a silicon heat sink, and evaluated for current-optical output characteristics.

The prototype device oscillates in the 1.3 μm band,
Current value at 5 ° C, 5mW is 40mA on average, 35mA minimum
The result is excellent and exceeds the best value of the conventional structure. Also, the maximum light output is 150 mW when cleaved on both ends,
300m by applying a highly reflective coating on one end surface
W is obtained, which is an improvement over the conventional structure.

FIG. 3 is a view for explaining a second embodiment of the semiconductor laser of the present invention, and shows a semiconductor laser having a structure different from that of FIG. N-InP on InP semiconductor substrate
Cladding layer _{36, n-In 0. 8} Ga 0. 2 As / In
The P-strained superlattice layer 35, p-InP32, and n-InP33 are sequentially crystal-grown. A mask is formed by photolithography, and stripe-shaped V-shaped or inverted trapezoidal grooves are formed by etching. After removing the mask, the n-InP, n-InGaAsP active layer 34,
By sequentially forming p-InP and growing the P-InGaAs contact layer 31, the semiconductor structure shown in FIG. 3 is obtained.
Also in this device, excellent low threshold and high temperature characteristics were obtained.

The present invention can be applied to semiconductor lasers having other structures. Further, other materials may be used for the superlattice structure of the current block structure. For example, in an InGaAsP / InP-based semiconductor laser, InAs, InSb, InGaSb, or a mixed crystal of these can be used as the well layer of the strained superlattice structure in addition to InGaAs. AlP, Ga as the barrier layer
P, AlAs, GaAs, AlSb, InP and mixed crystals thereof can be used.

In the AlGaAs / GaAs laser, I
An nGaAs / AlGaAs strained superlattice structure can be used. In addition, InAs, GaAs, In as well layers
Sb, GaSb and mixed crystals thereof can be used.
AlP, GaP, AlAs and mixed crystals thereof can be used as the barrier layer.

Others AlGaInP / GaAs, GaI
It can be applied to a semiconductor laser of III-V group material such as nP / GaAs system.

[0017]

The semiconductor laser having the current block structure of the present invention is excellent in low threshold and high temperature characteristics.
Not only as a hostile specification for 3 μm band subscribers, but also high output operation is possible because the leak current is suppressed. High output for 1.48 μm band fiber amplifier excitation or 1.55 μm band OTDR It can also be applied to semiconductor lasers. Also, good results can be expected when used in a DFB laser for a main line system, a semiconductor optical modulator, or the like.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of the present invention.

FIG. 3 is a diagram for explaining a semiconductor laser according to a second embodiment of the present invention.

[Explanation of symbols]

11, 31 p ⁺ -InGaAs 12, 32 p-InP 13, 33 n-InP 14, 34 n-InGaAsP active layer 15, 35 n-InGaAs / InP strained superlattice layer 16, 36 n-InP 17 n-In _{0 . 8 Ga 0. 2 As 18} n-InP

Claims (3)

[Claims] 1. A semiconductor laser having a current block structure, wherein a current block structure having a strained superlattice structure of compressive strain is formed on all or part of a pn junction interface where the substrate-side cladding layer and a portion other than the active layer are in contact with each other. A semiconductor laser comprising. 2. InGaAs having a current block structure
In a P / InP-based semiconductor laser, the In composition x is larger than 0.53 in all or part of the pn junction interface where the substrate-side cladding layer and the portion other than the active layer are in contact with each other.
A semiconductor laser comprising a current blocking layer having a strained superlattice structure in which _x Ga _{1 -x} As and InP are alternately laminated. 3. AlGaAs having a current block structure
In a / GaAs semiconductor laser, a current blocking layer having a strained superlattice structure in which InGaAs and AlGaAs are alternately laminated is provided at all or a part of a pn junction interface where the substrate-side cladding layer and a portion other than the active layer are in contact with each other. Characteristic semiconductor laser.