JPS63245987A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce the oscillation threshold current of a laser element and to improve the oscillation efficiency by forming an N-type clad layer of low and high concentration layers of specific concentrations, and forming the low concentration layer at a P-N junction side and the high concentration layer at the other. CONSTITUTION:An N-type clad layer is formed in a 2-layer structure on an active layer 4, a low concentration layer 61 of 5X10<17>cm<-3> or lower is formed at a P-N junction boundary side, and a high concentration layer 52 of 1X10<18>cm<-3> or more is formed thereon. Thus, the P-N junction is not remotely bonded, a hetero boundary between a P-type active layer 4 and an N-type clad layer 61 becomes a P-N junction to reduce the oscillation threshold current of a laser element and to improve the oscillation efficiency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser device, and relates to a method for controlling solid-phase diffusion of a dopant from an n-type cladding layer into a p-type layer in a heterojunction at a p-n junction interface. The present invention relates to a semiconductor laser device with improved characteristics.

[Conventional technology]

Figure 2 is a cross-sectional view showing an example of a conventional internal stripe semiconductor laser device, in which (1) is a p-type layer plate, (2) is an n-type current confinement layer, (3) is a p-type cladding layer, and (4) is a p-type active layer,
(6) is an n-type cladding layer, (7) is a cap layer, (8)
.

(9) is an electrode. In this semi-integrated laser device, T
1~2X10 cm with e as impurity dopant
The n-type cladding layer (6) with a high concentration of
) (e.g. Special Publication No. 57-17278)
9).

[Problem that the invention seeks to solve]

The points of the prior art to be solved by the present invention will be described below. The detailed structure and operation of the conventional internal stripe semiconductor laser device shown in FIG. 2 will be explained in detail. P-type GaAs (1) is used as the substrate, and n-type GaAs (2) is used as the current confinement layer (2).
aAs, cladding layer (3) is p-type GaAIIAs,
The cladding layer (6) is n-type GaAIAs, the cap layer (7) is n-type GaAs, and the active layer (4) is p-type GaAs.
In AIAs, the M mixed crystal ratio in the active layer (4) is made smaller than that in the cladding layers (3) and (6).

In this semiconductor laser device, the current injected between the electrodes (8) and (9) by the voltage applied so that the electrode (8) becomes positive is absorbed by the groove α due to the presence of the current confinement layer (2).
It flows only within. That is, in the parts other than structure (1), the p-type between the current confinement layer (2) and the p-type cladding layer (3)
- Since the n junction is reverse biased, no current flows and the groove (1
0) Current concentrates only inside. In addition, the p-type cladding layer (3) has a thickness of 0.3 μm or less, and a part of the light generated in the active layer (4) is absorbed by the current confinement layer (2) and the groove (
10) There is an effective refractive index difference between the upper part and the other part, and the light becomes active/i! (4) is confined in the upper part of the groove (10). That is, an optical waveguide is formed along the groove (10).

Incidentally, in the semiconductor laser device as described above, Sn is used as the n-type impurity portion of the n-type layer (6).

Te, etc., but 1~2XIOc to reduce the oscillation threshold current density and the resistivity of the n-type cladding layer (6).
A carrier concentration on the order of m is required.

When the oscillation wavelength becomes 800 m or less, the M mixed crystal ratio of the cladding layer needs to be 0.4 or more. In order to obtain an N type carrier concentration of 1 to 2 x 10 cm with an M mixed crystal ratio of 0.4 or more, impurities are added. As a dopant, Te, which has large segregation, is generally used. FIG. 3 shows the change in carrier concentration in the p-cladding layer when the amount of impurities in the p-type cladding layer is constant and the amount of Te in the n-type cladding layer is changed. As you will see, the Te concentration is 1 x 10 cm.
If it becomes more than that, the carrier concentration of the p-type cladding layer sandwiching the active layer decreases rapidly. This indicates that solid phase diffusion of Te in the n-cladding layer occurs into the p-type active layer and the n-cladding layer. This diffusion of Te causes remote junctions, an increase in the oscillation threshold current density,
This results in deterioration of the temperature characteristics of the laser. Also, Te is 10
Ga AtA doped at a high concentration of ``cm-3 or higher''
Clusters of Ga and Te and Al and Te are likely to occur in S, and these clusters do not become crystal defects, but form non-radiative recombination centers at the heterojunction interface, which is the heart of the semiconductor laser device. These things become factors that reduce the reliability of the semiconductor laser device.

[Means for solving problems]

In a semiconductor laser device, the present invention has a two-layer structure for the n-type cladding layer, and 2 to 5×10 A low concentration layer of 2 cm to 2 axio Cm is provided, and a high concentration layer of 2 to axio Cm is provided adjacent to it.

[Example 1] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing the configuration of one embodiment of the present invention;
The same reference numerals as in the conventional example in the figure indicate equivalent parts.

A current confinement layer (2) made of n-type GaAs is formed on a p-type GaAs substrate (1), and a striped pattern (10) reaching the substrate from the surface of this current confinement layer is chemically etched. form. Next, this groove (10)
Mg or G on the current confinement layer (2) including the inside of the
A p-type cladding layer (3) made of Ga1-xAlxAs with e as an impurity is grown to a thickness of 0.3 μm, and Mg
Or Ga1-yAl y A s with Ge as an impurity
An active layer (4) consisting of 0.1 to 0.13 μm is grown. Subsequently, 2 to 5×10 c of Te was deposited on the active layer (4).
A low-concentration n cladding layer (61) made of Ga1-z AlzAs doped to about 0.3 μm is grown to a thickness of about 0.3 μm, and a high-concentration n-cladding layer (61) made of Gat-zAAzAs doped with Te to about 2 to 3×10 cm is grown on top of this. Grow an n-cladding layer (62) to 1 μm. Here, the relationship between the M mixed crystal ratio of each cladding layer and the active layer is x = 2 and x>
y r z > y. Finally, n-type GaAs is placed on the high concentration n cladding layer (62) to make contact with the electrode.
Grow a cap layer (7) consisting of: A single liquid phase epitaxial growth process is performed from the n-cladding layer (3) to the cap layer (7). After these growths, electrodes (8
) and (9) are formed.

The operating principle of this semiconductor laser device is as described in [Problems to be Solved by the Invention]. Since the n-cladding layer forming the p-n junction interface has a low concentration, the interface with the active layer (4) has a high concentration of Te doped n-2.
There are far fewer defects serving as non-radiative recombination centers than in the case of the Rad layer, and there are also high! 1! Recommended Te doped layer to p
Since the diffusion of impurities into the shaped layer is suppressed, it is possible to reduce the oscillation threshold current, improve luminous efficiency, and significantly improve reliability without forming a remote junction. Also,
Even if a low concentration GaAjA s layer is provided, its thickness is about 30 to 40% of the n-type cladding layer, so the increase in element resistance is almost negligible, and the increase in thermal resistance is also no problem. .

[Example 2] A @2 embodiment of the present invention will be described below.

The structure of the semiconductor laser element is as shown in FIG. 1, as in Example 1. In the n-cladding layer of the 2J-structure, the low density G a t -z of 2~5X10 cm
Aj! The curvature of the M crystal ratio of the zAs layer (61) and the /-3fJ degree Gat-uAffiuAsl (62) of 2~3X10 cm is x = u>z, , r) = y*z>y
shall be. In this way, the low 9W layer (61 side At mixed crystal ratio ?2
By lowering the temperature below 11 degrees tU (62), the laser oscillation in the active layer is transmitted through the low ejection n-cladding layer (61).
More light seeps into the highly saturated n-cladding layer (6υ) through the Tet-high concentration (2~3X10
GaAjAs doped to a depth of about 1 cm) has many non-radiative recombination centers, and noise induced by backlight,
This results in a low-noise laser device with improved longitudinal mode instability and noise temperature characteristics. In addition, even in high-power lasers such as those used in optical disks, from the viewpoint of preventing deterioration of the laser beam emitting end face, it is important to create an element structure that increases the amount of light seeping from the active layer to the cladding layer. It is a positive means of improving reliability.

〔Effect of the invention〕

As explained above, the present invention combines p-type active no and high concentration Te.
In order to suppress the solid phase expansion of Te into the p-type layer, which occurs at the p-n junction interface formed in the doped n-type cladding layer,
-N low concentration Te of 2 to 5 x 10 cm on the junction interface side
A doped n-type cladding layer was provided. This prevents the pn junction from becoming a remote junction and allows SD type active no and n
The hetero interface with the shaped cladding layer becomes the p-n junction surface,
Reduces the oscillation threshold current of the laser element, improves oscillation efficiency,
It is possible to improve reliability. In addition, by lowering the M mixed crystal ratio in the low concentration layer of the 27m&n; type n-type cladding layer compared to the high concentration layer, it is possible to reduce the noise of the laser element.

Furthermore, in the present invention, T is used as an n-type doping impurity.
Although the explanation has been made using Su, Se, S, etc., similar effects can be expected.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of one embodiment of the internal stripe semiconductor laser device according to the present invention, and the second embodiment has the same structure. FIG. 2 is a cross-sectional view of a conventional internal stripe semiconductor laser device. FIG. 3 is a diagram showing a change of 4 degrees in the p and n cladding layers when the amount of Te in the n-type cladding layer is changed while the p-type dopant loading remains constant. 1...G a As substrate, 2... Current confinement layer, 3... P-type cladding layer, 4...
...p-type active layer, 6...Te-doped n-type cladding layer, 61...Te-doped lightly doped n-cladding layer, 62...Te-doped heavily doped n-cladding layer , 7... Cap layer, 8.9...
Electrode, 10...groove. 1-”””,

Claims (1)

[Claims] In a pn junction consisting of a p-type active layer and an n-type cladding layer, the n-type cladding layer is 5×10^1^7cm^-^3
A semiconductor consisting of two layers: a low concentration layer below and a high concentration layer of 1×10^1^8 cm^-^3 or more, with the pn junction side being the low concentration layer and the other being the high concentration layer. laser element.