JPH0467354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in multi-quantum well structure semiconductor lasers.

As a conventional multi-quantum well structure semiconductor laser
There is an AlGaAs/GaAs modified multi-quantum well structure semiconductor laser. The energy band diagram of this main part is shown in FIG. In the figure, 1 is an n-type cladding layer (n-Al _0.4 Ga _0.6 As), 2 is a multiple quantum well structure, and 3 is a P-type cladding layer (P-Al _0.4 Ga _0.6
As), 4 is a potential barrier layer (Al _0.2
5 _is a quantum well layer (GaAs).
As shown in the figure, in this example, the multi-quantum well structure 2 consists of five quantum well layers 5 and four potential barrier layers 4, and electrons and holes are formed in the very thin quantum well layer 5 (~100A). By being confined to , discrete quantization levels are generated. Due to such quantization effects, multi-quantum well structure semiconductor lasers achieve high performance, typified by ultra-low threshold values well below 1 KA/cm ² .

However, in a multi-quantum well structure semiconductor laser having such a structure, it is desirable to reduce the thickness of the multi-quantum well structure 2 in order to reduce the threshold current density. However, there is a contradictory fact that if the thickness is made too thin, light confinement in the multi-quantum well structure deteriorates and the threshold current density increases. Due to these circumstances, the multi-quantum well structure 2 cannot be made unnecessarily thin, and therefore it has been difficult to further reduce the threshold current density than before.

A second problem is that the quantum levels of the multiple quantum well layers 5 are different. That is,
The outer quantum well layer in contact with the n-type cladding layer 1 and the p-type cladding layer 3 has a quantum level energy larger than that of the inner quantum well layer because of the high potential barrier of the cladding layer. Therefore, a slight difference occurs between the quantum level of the outer quantum well layer and the quantum level of the inner quantum well layer. This difference broadens the gain spectrum of the quantum well laser, leading to characteristic deterioration such as an increase in threshold current.

An object of the present invention is to provide a multi-quantum well structure semiconductor laser in which optical confinement does not deteriorate even when the thickness of the multi-quantum well structure is reduced, and the threshold current density is therefore smaller than that of the conventional semiconductor laser.

The multi-quantum well structure semiconductor laser of the present invention includes:
a first cladding layer; a forbidden band formed on the first cladding layer and having a smaller forbidden band width than the first cladding layer;
a first semiconductor layer having E _g1 ; a multiple quantum well structure formed on the first semiconductor layer; and a first semiconductor layer formed on the multiple quantum well structure and having a forbidden band width of E _g1 . a second cladding layer formed on the second semiconductor layer and having a forbidden band width larger than the E _g1 , and a forbidden band smaller than the E _g1 inside the multiple quantum well structure. and a potential barrier layer sandwiched between the quantum well layers and having a forbidden band width approximately the same size as E _g1 . .

As the first embodiment of the present invention, AlGaAs/GaAs
A multi-quantum well structure semiconductor laser will be explained. FIG. 2 is an energy band diagram of the main parts of the multi-quantum well structure semiconductor laser of this example. In the figure, 21 is an n-type cladding layer (first cladding layer, n-Alxn GA1-xnAs, xn≧0.25,
Typically xn ~ 0.4) 22 is the first semiconductor layer (Alxg
Ga1−xg As, 0.1≦xg<xn, typically n−
Al _0.2 Ga _0.8 As, thickness 30-1000A), 23 is a multiple quantum well structure, 24 is a second semiconductor layer (AlxgGa1
-xg As, typically P-Al _0.2 Ga _0.8 As thickness
30~1000A), 25 is a P-type cladding layer (second cladding layer, P-Alxp Ga1-xp As xp≧0.25, typically xp~0.4), 26 is a quantum well layer (number of layers≧
2, Alxw Gal-xw As, 0≦xw<xg, typically non-doped GaAs, thickness≦200A, 27 is a potential barrier layer (number of layers = nw-1, Alxg Ga-
xg As typically undoped Al _0.2 Ga _0.8 As
Thickness ≦200A). In this embodiment, since the compositions of the first and second semiconductor layers and the potential barrier layer are the same, the forbidden band widths of these layers are all the same. Therefore, the quantum well layer 26a located on the outside and the quantum well layer 26 located on the inside
b are all surrounded by the same potential barrier height, and these quantum well layers 26
No difference in quantization level occurs between the two. Therefore, the spread of the quantization level is smaller than that of the conventional one, and the emission spectrum is narrow enough to realize a low threshold value. Further, in this structure, since there are the first and second semiconductor layers, the thickness of the optical waveguide layer can be made larger than that of the multiple quantum well layer 23. Therefore, even when the thickness of the multi-quantum well structure 23 is reduced, light confinement can be improved by optimizing the thicknesses of the first and second semiconductor layers. In this way, in the multi-quantum well structure semiconductor laser of this example, the spread of the quantization level between the multi-quantum well layers is small and the light confinement is good, so it achieves an even lower threshold current density than the conventional one. You can.

Next, the manufacturing method will be briefly described. FIG. 3 is a cross-sectional view of the multi-quantum well structure semiconductor laser of the first embodiment in which the electrode structure is an all-over electrode structure. In the figure, 31 is an n-GaAs substrate, 32
3 is a buffer layer (n-GaAs), 33 is a cap layer (P-GaAs), 34 is a P electrode, and 35 is an n electrode. Further, 21 to 25 in the figure are as described in the explanation of FIG. 2. In the manufacturing process, first, a buffer layer 32 and an n-GaAs substrate 31 are formed on an n-GaAs substrate 31.
A type cladding layer 21, an n-type guide layer 22, a multiple quantum well structure 23, a p-type guide layer 24, a p-type cladding layer 25, and a cap layer 33 are epitaxially grown. Crystal growth methods include MBE, MO-CVD, and VPE.
Any growth method may be used, such as the method or the LPE method.
Next, a P electrode 34 and an n electrode 35 are formed to complete the wafer process. Next, the wafer is cut into pellets using a wall cutter, etc., and attached to a slam or the like, and finally, lead wires are attached.

In the manufacturing method of this embodiment, the current injection structure with a full-surface electrode structure has been described, but the current injection structure is not limited to this, and other current injection structures such as a planar stripe structure, an oxide stripe structure, a proton irradiation stripe structure, a ridge waveguide structure, a buried structure, etc. It is clear that the present invention can be applied to the active region of the structure as well. In addition, in this example, as a material
Although AlGaAs/GaAs system was used, it is not limited to this.
InGaAsP/InP, InGaAlAs/InP, InGaAlP/
It is clear that the present invention is also applicable to other materials such as GaAs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an energy band diagram of a conventional AlGaAs/GaAs multiple quantum well structure semiconductor laser. FIG. 2 is a diagram showing an energy band diagram of the AlGaAs/GaAs multiple quantum well structure semiconductor laser according to the first embodiment of the present invention. FIG. 3 shows the first embodiment of the present invention.
1 is a cross-sectional view of an AlGaAs/GaAs multiple quantum well structure semiconductor laser. In the figure, 1...n-type clad layer, 2...multi-quantum well structure, 3...p-type clad layer, 4...potential barrier layer, 5...quantum well layer, 21...
First cladding layer (n-type cladding layer), 22... first semiconductor layer, 23... multiple quantum well structure, 24...
...Second semiconductor layer, 25...Second cladding layer (P-type cladding layer), 26...Quantum well layer, 27...Potential barrier layer, 31...N-GaAs substrate, 32...Buffer layer, 33... . . . cap layer, 34 . . . P electrode, 35 . . . n electrode.

Claims (1)

[Claims] 1 a first cladding layer, a first semiconductor layer formed on the first cladding layer and having a smaller band gap E _g1 than the first cladding layer, and a multilayer semiconductor layer formed on the first semiconductor layer. a quantum well structure, a second semiconductor layer formed on the multi-quantum well structure and having a forbidden band width of E _g1 ; and a second semiconductor layer formed on the second semiconductor layer and having a forbidden band width larger than E _g1 . a second cladding layer having a band width, sandwiched between the quantum well layer and at least two quantum well layers having a forbidden band width smaller than the E _g1 inside the multi-quantum well structure; and a potential barrier layer having a forbidden band width approximately the same size as E _g1 .