JPH0564478B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a method for manufacturing a heterojunction semiconductor laser device in which grooves are formed in a substrate for crystal growth.

<Prior art> When manufacturing a conventional semiconductor laser device, when growing a double-heterojunction multilayer crystal structure on a substrate with striped grooves, the grooves on the substrate of the first cladding layer are generally filled. It has a role. However, this method may cause some inconveniences. As an example, having a groove
P− with an AlAs molar ratio y of 0.6 or more on a GGaAs substrate
The case where Ga _1-y AlyAs is grown as a cladding layer will be explained. FIG. 1 is a cross-sectional view of a VSIS laser with a flat active layer in which a V-shaped groove is formed in the substrate.
Details of this semiconductor laser are described in Institute of Electronics and Communication Engineers technical report ED81-42, page 31 (July 1981). 1 is a P-GaAs substrate, 2 is an n-
GaAs current blocking layer, 3 is P-Ga _1-y AlyAs cladding layer, 4 is P-Ga _1-x AlxAs active layer, 5 is n-
A Ga _1-y AlyAs cladding layer and 6 an n-GaAs cap layer. Further, 7 is a V-shaped groove, and this portion serves as a current path. When trying to oscillate this internal stripe structure VSIS laser at a wavelength of 750 nm or less,
The AlAs molar ratio y of the cladding layers 3 and 5 must be 0.6 or more. The reason for this is that if the value is less than 0.6, carriers accumulated in the active layer 4 will leak into the cladding layers 3 and 5, leading to an increase in the threshold current and worsening of the temperature dependence of the threshold current, making it unusable for practical use. . In particular, even among the carriers of the active layer 4, since most electrons leak into the P-clad layer 3, it is necessary to set the barrier to electrons in the P-clad layer 3 as high as possible. This barrier not only depends on the AlAs molar ratio y, but also increases as the hole concentration of the P-clad layer 3 increases. For example, when the hole concentration is 5×10 ¹⁷ cm ^-3 , the barrier increases by about 50 meV (about 20% of the barrier). Therefore,
The hole concentration in P-clad layer 3 is at least 1×10 ¹⁸ cm ^-3
is necessary.

1×10 ¹⁸ cm in P-Ga _1- yAlyAs with y>0.6
To obtain a carrier (hole) concentration of ^-3 or higher, Mg is currently the most suitable impurity. The reason is that when the amount added is 0.3 at% or more, carriers (holes) of 1×10 ¹⁸ cm ^-3 or more
This is because the concentration can be easily obtained.

However, there is a phenomenon in which when Ga _1-y AlyAs is doped with a large amount of Mg, its growth rate slows down. The reason for this is thought to be that Mg acts to reduce the diffusion coefficient of As in the Ga solution. In particular, when y>0.6, adding 0.3 at% Mg causes the growth rate of Ga ₁ -yAlyAs to become very slow, and as shown in FIG.
It becomes difficult to completely fill the area. As a result, the active layer 4 becomes curved. This curved active layer is undesirable because it induces higher-order transverse modes. Even if the growth time of the P-clad layer 3 is lengthened in the growth process, it is very difficult to provide a flat layer for the active layer 4. In addition, the growth time is made very long so that the active layer 4
Even if the groove becomes flat, the thickness of the P-cladding layer 3 outside the groove becomes too thick, and no refractive index waveguide is formed. As mentioned above, the P-clad layer
No matter how the amount of Mg added to Ga _1-y AlyAs (y>0.6) is selected, it is difficult to manufacture a semiconductor laser with good characteristics at a high yield and reproducibility.

<Objective of the Invention> The present invention provides a new and useful semiconductor laser device that improves manufacturing yield and characteristic reproducibility in a heterojunction semiconductor laser in which grooves are formed in a substrate on which multilayer crystals for laser oscillation are laminated. The purpose is to provide a manufacturing method.

<Description of structure and effects> The present invention provides a current blocking layer formed on a substrate,
A substrate for crystal growth is prepared by processing a groove that will become a current path leading to the substrate, and a first cladding layer, an active layer, and a second cladding layer are sequentially successively grown on the substrate for crystal growth using a liquid phase epitaxial growth method. In a method of manufacturing a semiconductor laser device by growing a semiconductor laser device, a small amount (0.2 at.
After flattening the growth surface of the crystal layer by filling it with a crystal layer doped with Mg (0.3 at.% or less), the carrier layer is grown by growing the first cladding layer to which a large amount (0.3 at. The method is characterized in that a cladding layer whose concentration and layer thickness are appropriately controlled is deposited on a substrate for crystal growth, and a flat active layer is laminated thereon to form a multilayer crystal structure for laser oscillation. Since the grooves are filled with a crystal layer containing a small amount of Mg, the growth rate is not slowed down and the diffusion coefficient of As in the growth solution is maintained constant, allowing the grooves to be filled rapidly. As a result, the growth surface of the crystal layer is substantially planarized in a relatively short period of time. Next, by growing a cladding layer doped with Mg with sufficient carrier concentration and depositing a flat active layer on top of this, a perfect heterojunction is obtained that prevents carrier leakage from the active layer. .

The semiconductor laser device having the above structure has a low threshold current, good reproducibility of temperature characteristics of laser oscillation, and is a highly reliable device. Furthermore, manufacturing yields are greatly improved, making it possible to establish an efficient mass production line.

<Example> Hereinafter, as an example of the present invention, a VSIS semiconductor laser device that oscillates at a visible wavelength of 700 nm or less will be taken as an example and its manufacturing method will be described with reference to FIG. In the crystal growth method of this example, a crystal growth substrate with a V-shaped groove is placed on a holding table, and a boat containing a growth solution is moved to sequentially coat the growth substrate with the solution. , is based on the sliding liquid phase growth method that precipitates single crystals.

P-GaAs substrate (Zn doped, 1×10 ¹⁹ cm ^-3 ) 1
n-GaAs (Te) as a current blocking layer on the (100) plane of
Doped, 3×10 ¹⁸ cm ^-3 )2 is grown to a thickness of 0.6 μm by liquid phase epitaxial growth. after that,
A striped V-shaped groove 7 having a width of 4 μm is formed in the (110) direction by etching to a depth that reaches the substrate 1. The V-groove 7 removes the current blocking layer 2 from the substrate 1 and opens the current path. A P-Ga _1-z AlzAs trench filling layer (Z=0.7, Mg: 0.06 at.% added) 8, P-
Ga _1-y AlyAs cladding layer (y=0.8, Mg: 1.0at.%
addition) 9, P-Ga _1-x AlxAs active layer (x=0.3,
Mg: 0.03 at.% addition) 4, n-Ga _1-y AlyAs clad layer (y = 0.8, Te: 0.001 at.% addition) 5, n
- GaAs (Te: 0.003 at.% added) 6 is continuously grown by a liquid phase epitaxial growth method to form a double heterojunction multilayer crystal layer for laser oscillation. of each layer
AlAs molar ratio is 0<x<z≦y, 0.6z≦y<1
The following relational expression is satisfied. Mg in trench buried layer 8
Since the amount added is small, the growth rate is fast; the grooves 7 are completely filled in about 60 seconds, and the growth surface becomes flat after the growth is completed. At this time, both shoulders of the groove 7 are slightly melted back and have a rounded shape. Further, the thickness of the groove-embedding layer 8 on both sides outside the groove 7 was 0.1 μm. The thickness of each layer grown following the trench filling layer 8 is 0.1 μm for the P-clad layer 9, 0.08 μm for the P-active layer 4, and 0.1 μm for the P-clad layer 9.
- cladding layer 5 is 1μm, n-cap layer 6 is 1μm
m. Since the carrier concentration of the P-clad layer 9 has a large amount of Mg added, it exhibits a high concentration value of 3 × 10 ¹⁸ cm ^-3 , and the barrier to electrons in the active layer 4 is
The voltage is as large as 230 meV. Therefore, confinement of electrons in the active layer 4 at the heterojunction interface has a sufficient effect. When a P-side electrode and an N-side electrode are formed on the substrate 1 and the cap layer 6, respectively, and a current is injected, the current flows concentrated only in the region where the current blocking layer 2 of the groove 7 has been removed, and the corresponding active layer Laser operation starts within 4. The grooves 7 act as internal stripe structures for current concentration.

The VSIS laser of this example oscillated at a short wavelength of 680 to 700 nm, and its threshold current was as small as 70 mA on average. In addition, the temperature dependence of the threshold current is
It was small at 0.6mA/℃. Furthermore, most of the elements within the wafer oscillated with a threshold current of 100 mA or less, and the reproducibility was also good. Currently, a device with an oscillation wavelength of 683 nm has been obtained using CW (continuous) oscillation. This is the shortest CW oscillation wavelength of any semiconductor laser to date. (Appl.Phys−
Lett.vol.41, P.796, 1982) P-clad layer
Although the AlAs mixed crystal ratio is very large at about 0.6 or more, the hole concentration is as high as about 1×10 ¹⁸ cm ^-3 , so the threshold current is low and the device characteristics can be reproduced well.

The present invention is not limited to the above-mentioned GaAs-GaAlAs system.
It can also be applied to other materials such as InP-InGaAsP type GaAsSb-AlGaAsSb type.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic configuration of a VSIS laser. FIG. 2 is a cross-sectional view of a VSIS laser with a curved active layer. FIG. 3 is a sectional view of a main part of a semiconductor laser device showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... P-GaAs substrate, 2... n-GaAs current blocking layer, 3, 9... P-Ga _1-y AlyAs cladding layer, 4... P or n-Ga _1-x AlxAs active layer, 5...
...n-Ga _1-y AlyAs cladding layer, 6...n-
GaAs cap layer, 7...V-shaped groove, 8...P-
Ga _1-z AlzAs trench filling layer.

Claims (1)

[Claims] 1 A current blocking layer formed on a substrate is processed with a groove that becomes a current path to the first substrate to form a substrate for crystal growth, and a first cladding layer, an active layer and a second cladding layer are formed on the substrate for crystal growth. In the method of manufacturing a semiconductor laser device, in which a cladding layer is successively grown using a liquid phase epitaxial growth method, a groove with a small amount of Mg added is formed on the crystal growth substrate to fill the groove in the crystal growth substrate. A method for manufacturing a semiconductor laser device, characterized in that after growing a buried layer, the first cladding layer containing a large amount of Mg is grown to cover the trench buried layer and block carriers in the active layer. .