JPS59125686A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To effectively operate a current enclosing function even at high injection exciting level and to enable high output operation by containing a current blocking layer which is substantially equal in the forbidden band width to an active layer and thicker than the active layer in a current block structure multilayer semiconductor layer. CONSTITUTION:A mesa stripe 40 of (110) direction is formed by a photolithographic method and a chemical etching method with an etchant of hydrochloric acid on a (001) InP substrate 1. Then, an N type InP buffer layer 2, an InGaAsP active layer 3 and a P type InP clad layer 4 are sequentially grown on the substrate 1 by a liquid phase growth method to form a double hetero structure crystal 41. Then, two parallel grooves 10, 11 are formed on the crystal 41. At this time, the positional relationship between the shape of the surface of the crystal 41 before etching as designated by broken and the grooves 10, 11 after etching is determined. Then, it is again introduced into a crystal growth furnace to sequentially grow in 2-phase solution method, P type InP and N type InP current enclosure layers 5, 6, a P type InP buried layer 7 and a P type InGaAsP contacting layer 8 sequentially.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser used for optical communication and the like, and more particularly to a semiconductor laser in which current confinement in an active layer is improved and high output operation is possible.

A buried heterostructure semiconductor laser (hereinafter abbreviated as BHLD), in which a band-shaped active layer is surrounded by a semiconductor layer with a smaller refractive index and a larger forbidden band width, has features such as a low oscillation threshold and stable oscillation transverse mode. Therefore, it is being put into practical use as a light source for optical communications and optical information processing. In order to achieve good characteristics in this BHLD, it is necessary to effectively concentrate and flow current to the active layer, and various current blocking structures have been devised. As an example, FIG. 1 shows a dual channel planar BHLD devised by the inventors of the present application.
(hereinafter abbreviated as DC-PBHLD) is shown. This is an n-4nP buffer layer 2 on a flat InP substrate 1.
．． InGaAsP active layer 3, p-InE! Cladding layer 4
Two parallel grooves 10 and 11 are formed in the 211 heterostructure (DH) substrate on which the p-I
nP current confinement layer 5, n-InP current confinement layer 6,
A p-InP buried layer 7, p-InGaA, and sP contact layer 8'fc are sequentially formed, and p-side and n-side electrodes 30 are formed.
．． 31 was formed. This DC-PBHLD has two grooves 10.11 (7) + p- on the outside.
A current block structure having an n p n0 layer structure is formed. In this structure, there is In of the original DH wafer.
The GaA and sPi layers 3 are left as current blocking layers 21 and 22, and it has been confirmed that this works effectively for current concentration. That is, in DC-PBHLD, p-n
- Of the two types of transistors constituting the p-n run risk structure, the p-I with the higher gain n-p-n) run risk
An InGaAsP current blocking layer with a smaller bandgap is sandwiched between the nP base and the n-InP emitter,9 which significantly reduces the carrier transfer efficiency of this transistor and therefore n-p-n) run risk payoff decreases. As a result, the pnpn cell structure is difficult to turn on, and current is effectively concentrated in the active region. Generally, the active layer of a semiconductor laser is formed very thin in order to achieve a low threshold value, a low vertical radiation angle, and the like. For example, conventional DC-PBHL
In D, it is set to about 01 μm. Conventional DC-PB
In HLD, a current blocking layer with the same composition and same thickness as the active layer is formed in the current blocking structure, so the thickness of the current blocking layer is insufficient to realize effective current confinement, and therefore high This p-n-p-11 zyristor often turns on slowly at the injection excitation level, making high output operation somewhat difficult.

The object of the present invention is that even at a high injection excitation level, the structure of the Ms flow closure is such that the active layer has a band-like active layer, and has a smaller refractive index and a larger forbidden band width than the active layer Ii (lower refractive index and larger forbidden band width). and a multilayer semiconductor layer having a current block structure formed in contact with at least the outer side in the longitudinal direction of the semiconductor layer surrounding both sides of the active layer, the current block structure The multilayer semiconductor rv= is characterized in that it includes a current blocking layer whose forbidden band width is approximately equal to that of the active layer and which is thicker than the active layer.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view of a preferred embodiment of the present invention; FIG.
), (b) and (C') are cross-sectional views showing three stages in the manufacturing process of the embodiment. In this embodiment, the current blocking layers 21, 22 are thicker than the band-shaped active layer 20, and even at high injection excitation levels, the current blocking layers 21, 22 are
It was confirmed that the n-thyristor does not turn on and effective current confinement occurs, and the conventional DC-PBHL
D type was also capable of high output operation. The manufacturing method of this embodiment will be explained based on FIGS. 3(a), (b) and (C).

First, a <110> oriented mesa stripe 4o is formed on the (001) InP substrate 1 by photolithography and chemical etching using a hydrochloric acid etchant, with an upper width of about 5 μm and a height of 1 μm. Next, an n-InP buffer layer 2 and an I
An nGaAsP active layer 3 and a p-InP cladding layer 4 are sequentially grown to form a double heterostructure crystal 41. n-InP
The buffer layer 2 and the p-InP cladding layer 4 are grown using a supercooling method with a supersaturation degree of about 8°C, and the active layer 3 is grown using a so-called two-phase method in which InP crystals are not completely dissolved but are floating in the solution. The solution method was used. The thickness of layers 2 and 3.4 is 2μ each except for the mesa stripe 40.
m, 03 μm, and 1 μm. At this time, on the upper surface of the mesa stripe 40, the thickness of the layers 2 and 3°4 is
1.5 μm, 0.1 μm, and 0.7 μm, respectively. That is, when growing by a two-phase solution method with a relatively low degree of supersaturation, the growth rate on the mesa stripe is significantly lower than the growth rate on the other flat areas. In this example, by utilizing this property, InGa with different thicknesses
The AsP layer was fabricated using a gold crystal growth process. At this time,
Since the portion that will become the band-shaped active layer 20 is formed on the mesa stripe 40, the portion that will become the current blocking layers 21 and 22 is also formed at a position far from the substrate 1.

Next, the two parallel grooves 1 are formed in the double heterostructure crystal 41 using the photophosphorography method and the chemical enotyphragm method using bromine-methanol enchantment.
0,11e is formed. At this time, the positional relationship between the shape of the surface of the crystal 41 before etching shown by the dotted line in FIG. 3(C) and the groove 10.11 after etching is determined. That is, the active layer mesa stripe 23 including the band-shaped active layer 20 sandwiched between the two grooves 10 and 11 is the same as the original mesa stripe 4.
10. so that it is almost in the center of the 0 part, and two grooves 10.
11 is a mesa stripe 40 of a double heterostructure crystal 41
Make it possible to reach other parts. After that, it is placed in the crystal growth furnace again, and the current confinement layers 5 and 6 of p-InP and n-InP, the p-InP buried layer 7, and the p-nG
The aA and sP contact layers 8 are sequentially grown using a two-phase solution method. At this time, by appropriately setting the growth time of each layer, the first two layers 5 and 6 do not grow on the upper surface of the active layer mesa stripe 23, and the latter two layers 7 and 8 grow over the entire crystal surface. It is possible to do so. The thickness of layers 5, 6, and 7.8 is 0.5 μm, 1.5 μm, and 0.5 μm, respectively, in the flat part.
μm, 0.7 μm. Subsequently, the p-side electrode 30 was placed on the growth surface, and the substrate 1 was thinned by polishing, then gold was deposited on the n1'lll electrode 31 to form an alloy, and the pellet was cut out by cleaving, scribing, etc., and the cross section is shown in Figure 2. The fabrication of such an element is completed. FIG. 4 shows an example of the pulse current-light output characteristics of the embodiment of the present invention and the pulse current-light output characteristics of a conventional DC-PBHLD. The light output of an embodiment of the invention is shown by curve 50, as shown by curve 50, where the light output from one side is 1
While more than 50 mW is obtained, the characteristics of the conventional element in FIG. 1 are approximately 100 mW, as shown by curve 51.
At this point, output saturation becomes severe and higher output operation is impossible. This is because, in the embodiment of the present invention, the thickness of the current blocking layer 21,22 in the current blocking structure is thicker than that of the conventional one, so that this p-n-p-n silicon risk structure has a higher excitation level. This is because the leakage current flowing to areas other than the band-shaped active layer 20 is significantly reduced even in a highly implanted excited state. In the present invention, by forming a double heterostructure on a mesa stripe substrate, the band-shaped active layer 20 and the current blocking layer 21, 22 can be formed simultaneously, and the former can have good transverse mode stability and a low threshold value. This makes it possible to form a thin enough comb to allow the comb to be thicker, and a thicker comb to achieve a BHLD with significantly improved high-output characteristics, with approximately the same number of steps as a conventional BHLD.
was realized.

As detailed above, according to the present invention, it is possible to provide a semiconductor laser in which the 15i flow confinement function works effectively even at a high injection excitation level and is capable of high output operation.

[Brief Description of the Drawings] Fig. 1 is a sectional view of a conventional buried structure semiconductor laser, Fig. 2 is a sectional view of a preferred embodiment of the present invention, and Fig. 3(a).
, (b) and (C) are cross-sectional views showing the crystal at three stages of the manufacturing process of this example, and FIG. 4 is a pulse current-light output characteristic diagram. 1...Substrate, 2...Buffer layer, 3.
...Active layer, 4...Clad layer, 5, 6.
...Current confinement layer, 7...Buried layer, 8...Par contact layer, 10.11...
Clear, 20... Band-shaped active layer, 21.22... Current blocking layer, 23... Active layer mesa stripe, 30
．． 31... Electrode, 40... Mezza stripe, 41
1... Double heterostructure crystal. ],・zo,″′

Claims (1)

[Scope of Claims] G) A band-shaped active layer, a semiconductor layer having a smaller refractive index and a larger forbidden band width than the active layer, surrounding at least both longitudinal sides and upper and lower surfaces of the active layer; a multilayer semiconductor layer having a current block structure formed in contact with at least the longitudinal outside of the semiconductor layer surrounding both sides;
A semiconductor laser characterized in that the current blocking structure multilayer semiconductor layer includes a current blocking layer having a forbidden width approximately equal to that of the active layer and thicker than the active layer. (2) In the semiconductor laser described in the preceding item, the distance between the bottom surface of the substrate on which each of the semiconductor layers is formed and the active layer is greater than the distance between the bottom surface and the current blocking layer. .