JPH07114301B2 - Semiconductor laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser device, which has been rapidly used in recent years as a light source for various electronic devices and optical devices and whose demand is increasing.

(Prior Art) As a coherent light source for electronic devices and optical devices, important performances required for semiconductor lasers include low current operation and fundamental transverse mode oscillation. In order to realize these performances, the spread of the laser light is suppressed so that the current flowing in the laser element is concentrated near the active region where the laser light propagates,
And it needs to be confined. A semiconductor laser having such a structure is usually called a stripe type semiconductor laser, and an internal stripe type laser is one of typical stripe type semiconductor lasers.

Hereinafter, referring to the drawings, as an example of the conventional internal stripe laser as described above, a BTRS (Buried TWin
-Ridge Substrate Structure) type laser will be explained.

Figure 4 shows the structure of the BTRS laser, where 1 is p
Type GaAs substrate, 2 is n type GaAs current blocking layer, 4 is p type Ga _1-x A
l _x As clad layer, 5 are Ga _1-y Al _y As active layers (0 ≦ y <
x), 6 is an n-type Ga _1-x Al _x As cladding layer, 7 is an n-type GaAs cap layer, and 8 is a p-side ohmic electrode. Reference numeral 9 is an n-side ohmic electrode.

The manufacturing method and operation of the BTRS laser configured as described above will be briefly described below.

The conventional BTRS laser is formed by two crystal growth steps by the LPE method. First, the n-type GaAs current blocking layer 2 is formed on the p-type GaAs substrate 1 in the first crystal growth step. Then, a V-shaped groove having an internal stripe width w is formed by photolithography. Then, a double heterostructure including the active layer 5 is formed thereon, and ohmic electrodes 8 and 9 are formed on the p-side and the n-side, respectively. When (+) voltage is applied to the p-side electrode 8 and (-) is applied to the n-side electrode 9,
Of the p-type GaAs current blocking layer 2 and the p-type GaAlAs cladding layer 4
A voltage is applied in the opposite direction only to the junction portion, and the injection current flows only from the internal stripe width w, and the current concentrates on the active layer 5 immediately above, resulting in low current operation, basic operation. Transverse mode oscillation is realized.

(Problems to be Solved by the Invention) However, in the above internal stripe type structure,
If the layer thickness and carrier concentration of the GaAs current blocking layer 2 vary within one laser element or within the wafer surface, light emission from the active layer 5 causes the GaAs current blocking layer 2 to enter the n-type GaAs current blocking layer 2. The diffusion distance of the holes in the generated electron-hole pairs is larger than the thickness of a part of the n-type GaAs current blocking layer 2, and the n-type GaAs current blocking layer 2 and the p-type substrate 1 are Of the internal stripe structure, and as a result, the barrier due to the reverse pn junction forming the internal stripe structure expires, and the internal stripe structure is lost. Therefore, the operating current value required to obtain the same light output is increased, and the substantial current stripe width is increased, so that the light emitting portion in the active region is increased to cause multimode oscillation.

In view of the above problems, the present invention provides an electron-generated electron from the active layer 5 in the n-type GaAs current blocking layer 2 even if the layer thickness or carrier concentration of the n-type GaAs current blocking layer 2 varies.
(EN) Provided is a semiconductor laser device capable of effectively recombining holes in a hole pair with electrons to prevent the internal stripe structure from being invalidated, and having good reproducibility, low current operation, and fundamental transverse mode oscillation.

(Means for Solving the Problems) In order to solve the above problems, a semiconductor laser device of the present invention is a semiconductor substrate of one conductivity type, and on the semiconductor substrate,
A layer having a conductivity type opposite to that of the semiconductor substrate, having a bandgap smaller than that of any other layer and having a film thickness of 0.1 μm or more, and a barrier layer for blocking holes are alternately laminated in three or more layers;
Further, a multilayer current blocking layer having a groove reaching the semiconductor substrate at a predetermined position, a multilayer thin film having a two-layer hetero structure including an active layer formed on the current blocking layer including the groove, and the semiconductor substrate. And an electrode respectively provided on the multilayer thin film.

(Operation) With this configuration, a barrier is provided so that the minority carriers in the layer having a conductivity type opposite to that of the substrate are effectively recombined with the majority carriers, and the diffusion distance of the minority carriers is substantially reduced, It is possible to realize a semiconductor laser device having an internal stripe structure capable of low current operation with good reproducibility and fundamental transverse mode oscillation.

(Example) Hereinafter, the Example of this invention is described, referring drawings.

FIG. 1 shows a cross section of a semiconductor laser device according to an embodiment of the present invention. In FIG. 1, 1 is a p-type GaAs substrate, 10 is a current blocking layer composed of a multilayer thin film, and 4 is p-type GaAlAs.
The cladding layer, 5 is a GaAlAs active layer, 6 is an n-type GaAlAs cladding layer, 7 is an n-type GaAs cap layer, 8 is a p-side ohmic electrode, and 9 is an n-side ohmic electrode.

FIG. 2 is a diagram showing a manufacturing process of the semiconductor laser according to the present invention, in which 1 is a p-type GaAs substrate, 10 is a multilayer current blocking layer, and 3 is a photoresist film. FIG. 3 shows a multilayer current blocking layer.
10 shows a cross section of an example, 1 is a p-type GaAs substrate, 2 is an n-type GaAs layer, 11 is a GaAlAs barrier layer, and 4 is p-type Ga.
The AlAs clad layer.

Next, a specific manufacturing method will be described. First, here, a p-type GaAs substrate is used as the substrate. This p-type GaAs
On the (100) plane of the substrate 1 (carrier concentration> ~ 10 ¹⁹ cm ^-3 ), stripes of width 50 μm with a pitch of 250 μm are formed parallel to the <01> direction with a photoresist film, and the height is 1.5 μm by chemical etching. To form a ridge. After the surface is washed to remove the photoresist film, a metal-organic vapor phase epitaxial growth method (hereinafter referred to as MOCVD method) is applied to the p-type GaAs substrate 1 having the ridge to a thickness of 0.3 as shown in FIG. μm n-type GaAs layer 2 (carrier concentration ~ 5 x 10
¹⁸ cm ^-3 ), 3 layers, GaAlAs barrier layer 11 with a thickness of 0.05 μm 2
Layers alternately grown epitaxially, total 5 layers, film thickness 1μ
The m current blocking layer 10 is formed. An example of the crystal growth conditions at this time is as follows. The growth temperature is 750 ° C. and the growth rate is 3
μm / hour, total gas flow rate 5 l / min, supply molar ratio V / III ratio of group V element to group III element was 20.

Further, as shown in FIG. 2, a photoresist film 3 is coated on the multi-layered current blocking layer 10, and a part of the central portion of the ridge has a width of 5 mm.
After removing the stripes of μm, chemical etching is performed using the stripes as a mask. The etching is performed until a part of the multilayer current blocking layer 10 is completely removed in the depth direction of the groove as shown in FIG. 1, that is, until the p-type GaAs substrate 1 is exposed. Here, the depth of the groove was 1.2 μm. After that, the photoresist film 3 is removed, the surface of the substrate is cleaned, and then a double hetero structure is grown by a liquid phase epitaxial method. Liquid phase epitaxial growth is performed under the growth conditions of a growth temperature of 850 ° C., a supersaturation degree of 7 ° C., and a cooling rate of 0.5 ° C./min, and the layers described below are sequentially grown. That is, as shown in FIG. 1, a p-type Ga _1-x Al _x As cladding layer 4 is formed on the p-type GaAs substrate 1 on which a multi-layered current blocking layer 10 is formed in a flat portion of 0.3.
μm, Ga _1-y Al _y As active layer 5 (0 ≦ y <x) is 0.08 μm,
The n-type Ga _1-x Al _x As cladding layer 6 was grown to 2 μm, and the n-type GaAs cap layer 7 was grown to 1.5 μm. A p-side ohmic electrode 9 is formed of AuZn on the p-type GaAs substrate 1, and an n-side ohmic electrode 8 is formed of AuGeNi on the n-type GaAs cap layer 7.

Mount the semiconductor laser manufactured as described above,
When a current is passed, the current is narrowed by the w stripe width shown in FIG. When an example of typical laser characteristics in a wafer is expressed by a threshold current value, a low threshold current value of 35 mA was obtained at w = 2 μm, and oscillation was stable fundamental transverse mode oscillation. Compared with the conventional BTRS type laser with a single current blocking layer, in the configuration of the present invention, the dispersion of the threshold current value in 30 elements is about 2/3 of the conventional one, and the effective minority carrier It shows that the diffusion length is shortened and the current blocking effect is working effectively.

In this embodiment, the GaAs-based and GaAlAs-based semiconductor lasers are described, but the present invention can be similarly applied to a semiconductor laser device made of a compound semiconductor containing InP-based or other multi-element mixed crystal system. Of the multiple current blocking layers,
A non-doped layer, except for the layer showing the conductivity type opposite to the substrate,
Either p-type layer or n-type layer may be used.
Either may be used.

(Effects of the Invention) As described above, according to the present invention, it is possible to easily form the internal stripe structure with good reproducibility, and as a result, it is possible to realize a high performance of fundamental transverse mode oscillation at a low threshold current value. A semiconductor laser device can be provided, and its practical effect is remarkable.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a diagram showing a manufacturing process of the device, and FIG.
FIG. 4 is a sectional view of an example of a multilayer current blocking layer, and FIG. 4 is a sectional view of a conventional semiconductor laser device. 1 ... p-type GaAs substrate, 2 ... n-type GaAs layer, 3 ... photoresist film, 4 ... p-type GaAlAs cladding layer, 5 ... GaAlAs active layer,
6 ... n-type GaAlAs cladding layer, 7 ... n-type GaAs cap layer,
8 ... p-side ohmic electrode, 9 ... n-side ohmic electrode, 10
... Multi-layered current blocking layer, 11 ... GaAlAs barrier layer, w ... Internal stripe width.

Claims (1)

[Claims] 1. A semiconductor substrate of one conductivity type, and a layer having a conductivity type opposite to that of the semiconductor substrate and having a bandgap smaller than that of any other layer and having a film thickness of 0.1 μm or more on the semiconductor substrate. And three or more barrier layers for blocking holes are alternately laminated, and a multilayer current blocking layer having a groove reaching the semiconductor substrate at a predetermined position, and formed on the current blocking layer including the groove. A semiconductor laser device comprising: a multi-layer thin film having a two-layer hetero structure including an active layer; and an electrode provided on each of the semiconductor substrate and the multi-layer thin film.