JPS60134489A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To make the increase of an output and the improvement of reliability coexist by keeping a difference between the mean refractive index of an active layer and the refractive index of a clad layer within a specific value. CONSTITUTION:An I-Ga1-xAlxAs clad layer 2', an active layer 3' having superlattice structure and an I-Ga1-yAlyAs clad layer 4' are formed on a semi-insulating (I) GaAs substrate 1'. A P type conductive impurity and an N type impurity are introduced up to depth penetrating the layer 3' from one part of the surface of the layer 4', and a P type conductive region 10 and an N type conductive region 11 are formed. Consequently, superlattice structure is collapsed in each conductive region, and mean compositions are obtained. Accordingly, the refractive index of the active layer is made higher than those of impurity introducing regions holding the active layer, and a mode in the horizontal direction is controlled. A mean refractive index through which the refractive indices of a quantum well layer and a barrier layer are obtained as the value of a bulk may be made smaller than the refractive indices of the clad layers, refractive-index waveguide is enabled when a difference between both is -0.5-+0.1, and gain waveguide is also enabled when the value is -0.5-0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a high-output and highly reliable semiconductor laser which is controlled in an optical mode.

[Background of the invention]

Conventional semiconductor lasers, which are designed to increase output by increasing the optical spot size, often suffer from the drawbacks of a small optical confinement coefficient, a high threshold current density, and a short lifetime.

[Purpose of the invention]

An object of the present invention is to provide a semiconductor laser that oscillates in the fundamental transverse mode and has high output and high reliability.

[Summary of the invention]

FIG. 1 is a sectional view of a substrate grooved stripe type semiconductor laser which is an example of a refractive index guided semiconductor laser. In the figure, 1 is a semiconductor substrate, 2 and 4 are cladding layers, 3 is an active layer, 5 is a cap layer, and 6 is an impurity diffusion layer.

7 is a concave groove. Alternatively, 12 and 13 are each electrodes.

In such a structure, if the fundamental transverse mode is to be maintained up to 100 mW, the active layer must be set to about 300 A or less and the light spot size must be about 2 μm><6 μm. At this time, the optical confinement coefficient F must be 5 or less, and is about 3=4, which is F of the 1-channel laser whose reliability has been confirmed. Mutual current density Jtb
is given by the following equation in a normal DH laser.

Jth (A/crr?)=4.5x10”d+1.0
xlO"d/7' where d is the thickness of the active layer given in μm. As can be seen from this equation, as F becomes smaller, the values of Jrh and the carrier density in the active layer Jth/d increase. Reliability deteriorates.In a normal laser, specifying one oscillation wavelength determines the refractive index of the active layer(f).Therefore, in order to increase the spread of light in the direction perpendicular to the junction, it is necessary to It is necessary to make the active layer thinner or to increase the refractive index of the cladding layer sandwiching the active layer.However, as mentioned above, making the active layer thinner requires decreasing F and increasing the refractive index of the cladding layer. Increasing the refractive index of the active layer reduces the band gap difference between the active layer and the cladding layer, which worsens the carrier confinement effect.

FIG. 2 shows the band structure of the active layer and cladding layer applied to the present invention. In FIG. 2, 8 indicates the band of the quantum well layer, and 9 indicates the band of the barrier layer. The active layer consists of a quantum well layer with a thickness of Lz (5 to 300 nm) and a thickness LB (5 to 300 nm) of a forbidden band than this quantum well layer.
A) has a superlattice structure in which barrier layers are alternately arranged. Here, if the number of quantum well layers is Nz, the refractive index is nz, the number of barrier layers is NB, and the refractive index is nB, then the average refractive index of the active layer is π. tlva is given by the following equation.

Therefore, if the refractive heavy metals of both cladding layers sandwiching the active layer are n(, and nc, respectively, πaptly.−ncl
and π. By reducing the size of tlm-nC2, that is, the refractive index difference, the light spot size can be increased without making the active layer particularly thin. In addition, the barrier layer works effectively and the carriers can be effectively confined in the active layer.

Therefore, according to the present invention, it is possible to realize a semiconductor laser in which the optical confinement coefficient F is relatively large, carriers are effectively confined, and the optical spot size is large.

As described above, by forming the active layer into a superlattice structure, the oscillation wavelength and the refraction weight of the active layer can be set independently to some extent. In order to lower the refractive index of the active layer, the thickness LB of the barrier layer is increased.

It is effective to reduce the refractive index nB.

However, when carriers are vertically injected from the cladding layer sandwiching the active layer as in many conventional semiconductor lasers, if the barrier layer is thick and its forbidden band width is large, the carrier injection efficiency deteriorates. The semiconductor laser device described in claim 2 is as follows.

It is designed to solve this problem, and has a structure that simultaneously controls the transverse mode in the horizontal direction.

FIG. 3 is a sectional view showing another embodiment of the present invention. The figure is a cross-sectional view taken along a plane perpendicular to the direction in which light travels. Here, an all-semiconductor laser is a GaAS-○aA, eAS-based semiconductor laser. Figure 3 shows semi-insulating (hereinafter abbreviated as i) GaAS.
Upward of the substrate 1', i -Ga, -X
-y AJl? yA s cladding layer 4' is laminated and 1Ga
A p-type conductive impurity and an n-type impurity are introduced from a part of the surface of the l-yAAyAs cladding 4' to a depth of 1 penetrating the active layer to form a p-type conductive region 10. An n-type conductive region 11 is formed. As a result, the superlattice structure within each conductive region becomes dull, resulting in an average composition. Therefore, the forbidden band width of the quantum well layer in the active layer sandwiched between each conductive region is smaller than the forbidden band width of the region where the superlattice is collapsed, and carrier injection is efficiently performed from the sides of the active layer. . Also, G
aA Swamp As has an impurity concentration of ~5 x 10” cr
There is a tendency for the refractive index to decrease as the value increases from n to 1. Therefore, the refractive index of the active layer is higher than that of the impurity regions that sandwich the active layer, and the horizontal mode is controlled. .

Furthermore, it is known that when the thickness of the barrier layer becomes approximately 45 nm or more, the refractive index of the superlattice becomes several factors higher than its average refractive index ()4ef, '1', 5uzuki
andl(, Qkamoto, J, 1electron
ic Materials 12 (1983) p, 39
7). Therefore, by setting the thickness LB of the barrier layer to between 45 and 300 layers, the refractive index of the active layer can be increased and refractive index waveguide can be realized. The refractive index of the quantum well layer and barrier layer is

The average refractive index π, which is assumed to be the same as the bulk value, is the refractive index n of the cladding layer (it does not matter if it is more or less, π−n c = −0,2 to +0.1). if there is,
Refractive index waveguide is possible. Also, π-n(, knee 0.5~0
If so, gain waveguide can be used.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. First, a method for manufacturing the semiconductor laser device shown in FIG. 4 will be described. 1G a on n”-GaAS substrate 1
o, 7 AAO, S A S cladding layer 2', GaAS
quantum well layer (100 layers thick) 101 and GaoaA-
Active layer 3' with a superlattice structure in which barrier layers (100 layers thick) 111 of 606As are arranged alternately (however, both the quantum well layer and the barrier layer are doped with Zn), 1-GaO
, 7A-6o, and s A S cladding layer 4' is sequentially grown by metal organic pyrolysis vapor deposition (MO-CVD). 81 ions are implanted from a part of the surface of the cladding layer 4' to a depth reaching the n+-GaAS substrate 1 to partially destroy the superlattice structure and form an n-type impurity region 11.

Next, after a 5io2 insulating film 14 is sputter-deposited.

As shown in the figure, patterning is performed using a photoresist process.

Then, Zn is selectively diffused to reach the active layer 3-2, thereby partially destroying the superlattice structure and forming the p-type impurity region 10. lastly.

A semiconductor laser device as shown in FIG. 1 is manufactured by forming multiple p-type electrodes 12 and n-type electrodes 13 by vapor deposition.

In this example, a high-output, highly reliable laser was realized in which the fundamental transverse mode was maintained at an optical output of 100 mW'1 and continuous oscillation was possible for more than 2000 hours at 7(I', 100 m'W).

In addition to the diffusion method and ion implantation method shown in the embodiment, the conductive regions 10 and 11 can also be formed by buried growth using etching and liquid phase growth. Further, the present invention provides GaA! Laser materials other than As-based, such as InGaA
The present invention can be similarly applied to semiconductor lasers using compound semiconductors such as SP-based and InGaP-based semiconductors.

[Effects of the Invention] According to the present invention, it is possible to reduce the difference in refractive index between the active layer and the cladding layer while effectively confining carriers. The large confinement coefficient has the effect of achieving both high output and high reliability. As a result of device fabrication, even if the active layer is as thick as about 0.2 μm, the fundamental transverse mode is maintained up to 100 mW, and the optical confinement coefficient F is a large value of about 0.2. At 700.100 mW, devices with an average lifespan of 2000 hours or more were obtained with good yield. From the above, it was found that the present invention is considerably effective in achieving both high output and high reliability.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional substrate grooved stripe laser.
FIG. 2 is a band structure diagram of an active layer and a cladding layer having a superlattice structure according to the present invention, FIG. 3 is a cross-sectional view of a semiconductor laser according to the present invention, and FIG. 4 is a cross-sectional view of a device according to an embodiment of the present invention. Ru. 1-” GaAS substrate, 1’・1-eaAs substrate, 2
-n-GaAAAS cladding layer, 2'...1-GaA
! AS cladding layer, 3... normal GaA, 13AS active layer, 3'... p-type active layer having superlattice structure, 4.
...I)-GaAJ3AS cladding layer, 4'...-1-
QaA shadow As cladding layer, 5...n-GaAS cap layer, 6...7. n diffusion layer, 7...groove on substrate, 8
...Band of quantum well layer, 9...Band of barrier layer,
10...n-type conductive region, 11...n-type conductive region, 1
2...n-type electrode, 13...n-type electrode, 14...3rd m Continued from page 1 [Phase] Inventor Naoki Kayane Kokubunji City Higashi Koigakubo Research Institute 0 Inventor Shun Kajimura Kokubunji City Higashi Koigakubo Research Institute

Claims (1)

[Claims] 1. A first semiconductor layer having a refractive index n1 and a second semiconductor layer having a refractive index n1.
A third semiconductor layer sandwiched between semiconductor layers includes a quantum well layer having a refractive index of nz and a thickness of Lz ranging from 5 to 300 nm, and a quantum well layer having a refractive index of nB and 5 It has a superlattice structure in which barrier layers with a thickness LB ranging from 30 to 300 nm are alternately arranged, and the average refraction n of the third semiconductor is composed of Nz quantum well layers and N++ barrier layers.
z LZNZ+n1LBN11 rate 1. When expressed as 6--75.7337, -, b n
The values of s"1 and 6-n2 are both -0.5 or +0.1
A semiconductor laser device characterized by being in the range of. 2. In the semiconductor laser device according to claim 1, the first and second semiconductor layers are semi-insulating and non-conductive; Second. A semiconductor laser device characterized in that a first conductive region is provided on at least one side of the third semiconductor layer, and a second conductive region is provided on the other side of the third semiconductor layer so as to sandwich the third semiconductor layer from the sides.