JPH04330794A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a lateral mode control type semiconductor laser having high reliability and a high efficiency. CONSTITUTION:A mesa side of a current injection stripe 11 state formed of double hetero structures 2-4 is covered with a multiple ultrathin film layer (so-called a multiple quantum barrier-MQB-layer 10) in which two types of semiconductor ultrathin film layers having different energy gaps are alternately deposited so that the total thickness of the layers is a thickness or less in which a phase difference between electrons incident to the layer and reflected electrons is about odd times as large as pi to maintain coherence of the electrons.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable semiconductor laser with excellent transverse mode control characteristics.

0002

2. Description of the Related Art Current injection lasers used in optical communications, optical information equipment, displays, etc. have a double heterostructure in which an active layer is sandwiched between cladding layers of a semiconductor having a larger energy gap. Furthermore, in order to maintain the horizontal transverse mode as a single fundamental mode, a structure is adopted in which a refractive index distribution is provided in a direction parallel to the junction. FIG. 2 shows an example of a structure according to the prior art (IEEE J. Quantum Elec
tron. (IEE Journal of Quantum Electronics) Volume QE16, p.
．． 205 (1980)) as viewed from the laser beam emitting end face. The striped region into which current is injected extends in a direction perpendicular to the plane of the paper. This conventional example is a so-called buried heterostructure and is configured as follows. n-G
A Darb heterostructure in which an Al0.07Ga0.93As active layer 203 is sandwiched between an n-Al0.35Ga0.65As cladding layer 202 and a p-Al0.35Ga0.65As cladding layer 204 is formed on an aAs substrate 201, and this double heterostructure portion A current injection stripe portion 206 is formed in a mesa shape into a stripe shape for current injection, and this double heterostructure current injection stripe 206 is buried with an n-Al0.35Ga0.65As buried layer 210 to form a buried heterostructure. . By creating a refractive index difference in the horizontal direction in the junction in this way, light is confined in the horizontal and lateral directions, and single horizontal transverse mode oscillation is obtained. Also, p-Al0.35Ga0.65A
s cladding layer 204 and n-Al0.35Ga0.65A
The potential barrier between the s buried layer 210 and the p-
Al0.35Ga0.65As cladding layer 205 and Al
Due to the difference in potential barrier between the 0.07Ga0.93As active layer 203 and the stripe region 203, the injected current is
I am trying to limit it to 06.

0003

According to the prior art described above, it is difficult to eliminate leakage current to the buried layer. Furthermore, even if an attempt is made to make the buried layer a high-resistance layer, it is difficult to obtain a high-quality, high-resistance semiconductor layer. because,
In order to obtain a high-resistance semiconductor layer, it is necessary to introduce impurities such as oxygen, chromium, and iron that form deep levels to capture carriers, which significantly impairs the quality of the buried interface on the mesa side. It's for a reason. This makes it difficult to maintain high quality as a laser element. Thus, the conventional structure has the drawbacks mentioned above.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks by utilizing the properties of carriers in semiconductor multiple ultra-thin film layers.
Our objective is to provide highly reliable, high-power semiconductor lasers.

[0005]

[Means for Solving the Problems] The gist of the present invention is to provide a laser active region in which a current is injected in a stripe pattern, and in which two types of semiconductor ultra-thin film layers having different energy gaps are alternately formed. The total thickness of the ultra-thin film layer is a multilayer film in which the phase difference between the electrons incident on the ultra-thin film layer and the reflected electrons is approximately an odd multiple of π, and is less than the thickness at which electron coherence is maintained. The structure is such that the striped active region is covered with an ultra-thin film layer. Methods for forming multiple ultra-thin film layers include metal organic pyrolysis vapor phase epitaxial method (MOVPE method) and molecular beam epitaxial method (MB
Method E), etc., regardless of the method. In addition, examples of semiconductor materials include AlGaAs, GaIn. PAs-based, AlG
It is applicable to any case, regardless of the material type, such as aInP type, AlGaInAs type, AlGaAsSb type, ZnSeS type, and others.

[0006]

[Operation] Figure 3 shows the multilayer ultra-thin film structure (hereinafter MQB) of the present invention.
(abbreviated as ) is shown below. Ga0.5 In0.5 P/Al0.5 In0.5 used as visible light laser material.
The function of MQB consisting of 5 P is shown (IEICE technical research report OQE90 (1990) p.
39). FIGS. 3A and 3B show energy band diagrams of conduction bands for the MQB structure in the layer stacking direction, and are denoted by MQB1 and MQB2, respectively. Both Al0.
5 In0.5 P barrier layer 31 and Ga0.5 In0
．． 5 P well layer 32. Ga0.5 In0.
5 MQB is formed on the P layer 33. Al0 in order
．． 5 In0.5 P barrier layer, Ga0.5 In0.
5 P well layers are formed alternately. 1st layer Al0.5
The In0.5P barrier layer has a thickness of 10 nm, and the other barrier layers have a thickness of 3 nm. Finally, Al0.5 In0.5
A case where the P layer 34 is coated is shown. In MQB1, Ga
0.5 In0.5 Ga0 in order from the side closest to the P layer 33
．． 5 In0.5 P well layer width 0.71 nm, 1
．． 2nm, 1.67nm, 2.14nm, 2.62nm
In addition, in MQB2, the thickness of all Ga0.5 In0.5 P well layers is 1.67 nm. The number of layers is determined so that the total thickness is approximately the coherence length of electrons. At this time, Ga0.5 In0.5 P layer 3
The electron energy of the electron reflectance seen from the 3 side (Ga0.
The dependence (value measured from the bottom of the conduction band of 5In0.5P) is shown in FIG. 3(c). The dotted line is for MQB1,
The one for MQB2 is shown by a solid line. Also, arrow A is Al
The energy value at the bottom of the conduction band of 0.5 n0.5 P is shown. As shown in this figure, Ga0.5 In0.5
From the P layer 33, this MQB layer has a 100% reflectance even to electrons with an energy approximately 370 meV higher than the bottom of the conduction band of Ga0.5 In0.5 P. This means that Ga
0.5 In0.5 Barrier from P layer is Al0.5 I
n0.5 higher than that of the P layer alone, generally (Alx
Ga1-x)0.5 In0.5 P(0≦x<1
), when this MQB is used as an electron barrier, A
An effectively higher barrier than l0.5 In0.5 P is obtained. The above discussion is about electrons, but the same can be said about holes. Therefore, (Aly Ga1
-y )0.5 In0.5 P layer is formed into p-type and n-type (
Alz Ga1-z )0.5 In0.5 P layer (0
When the aforementioned MQB layer is formed so as to be in contact with each layer on the sides of the double heterostructure sandwiched by ≦y<z<1) and a current is injected between the p-n layers, no current is injected into this MQB layer, No leakage current occurs due to the MQB layer. Therefore, a semiconductor film that does not generate leakage current can be obtained without making such an MQB layer high in resistance.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of an embodiment of the present invention viewed from the laser emitting end face side. MOVP on n-GaAs substrate 1
By the E method, a 1 μm thick n-(Al0.7Ga0.3
)0.5 In0.5 P cladding layer, thickness 0.1μ
m(Al0.1 Ga0.9)0.5 In0.5
P active layer 3, 1 μm thick p-(Al0.7 Ga0
．． 3) 0.5 In0.5 P cladding layer 4, thickness 0
．． A 1 μm p-Ga0.5 In0.5 P layer 5 is formed in this order. Next, a SiO2 film is formed only on the current injection stripe 11, and the double heterostructure layers 2 to 5 are removed by chemical etching using a hydrochloric acid-based etchant in the area outside the stripe, and the current injection stripe portion is formed in a meza shape. leave. Furthermore, an MQB layer 10 is formed on the mesa side surface and the exposed surface of the GaAs substrate 1 using the aforementioned SiO2 film.
is formed by MOVPE method. The structure is the same as that of MQB1 described in the operation section. In other words, the first 10n
m of Al0.5 In0.5 P, followed by 3n
G through a Al0.5 In0.5 P layer with a thickness of
The a0.5 In0.5 P layer is sequentially 0.71 nm, 1.
It is formed to have a thickness of 2 nm, 1.67 nm, 2.14 nm, and 2.62 nm. After that, Al0.5 In0.5 P
A buried layer 6 is grown to bury the entire mesa side. Subsequently, the SiO2 film on the current injection stripe portion 11 is removed, and a p-GaAs layer 7 is grown on the entire surface. After this,
A p-electrode 8 and an n-electrode 9 are formed by a vapor deposition method or the like. Each layer may be formed by an MBE method other than the MOVPE method, and does not depend on the manufacturing method. The mesa formation method does not depend on the manufacturing method, such as a dry etching method other than a chemical etching method.

This embodiment is a visible light semiconductor laser that oscillates at a wavelength of 650 nm. p-Ga0.5 In0.5
P layer 5 is p-(Al0.7 Ga0.3)0.5
This is intended to reduce the potential barrier generated at the interface between the In0.5P cladding layer 4 and the p-GaAs layer 7, thereby reducing electrical resistance. In this embodiment, as described in the operation section, since there is no leakage current to the MQB film, leakage current flowing through the buried layer can be eliminated. This makes it possible to suppress an increase in operating current due to the buried heterostructure. Also, G in MQB
a0.5 In0.5 P is an ultra-thin film and does not absorb light at the oscillation wavelength due to its quantum effect. Therefore, MQ
There is no increase in operating current due to light absorption due to B formation. Therefore, in this example, a single fundamental transverse mode oscillation laser with low operating current and high efficiency was realized. Also MQB
The quality of the interface with the membrane and end face is maintained high, and the outermost surface of MQB that is exposed to air is made of Ga0.5 In0.5 P.
Therefore, it is resistant to oxidation and highly reliable. In this example, the MQB layer had a specific film composition and film thickness, but
There are many combinations in which similar effects can be obtained with other film compositions and film thicknesses as long as they meet the scope of the claims. Although the details have been explained above using AlGaInP-based materials, other semiconductor materials such as AlGaAs-based, AlGaInAs-based, and GaInP
Similar effects can be obtained using As-based, ZnZeS-based, other materials, or a combination of these materials.

[0009]

[Effects of the Invention] As described above, by adopting the structure of the present invention, it is possible to obtain a coating film that is stable, high quality, and does not generate leakage current. A stable semiconductor laser can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the structure of a transverse mode control laser according to an embodiment of the present invention, as viewed from the light emitting end face.

FIG. 2 is a diagram schematically showing the structure of a conventional transverse mode control laser as seen from the light emitting end face.

FIG. 3 is an explanatory diagram used to describe the action of the present invention.

[Explanation of symbols]

1,201 n-GaAs substrate 2 n-(Al0.7 Ga0.3)0.5
In0.5 P cladding layer 3 (Al0.1 Ga0.9)0.5 In
0.5 P active layer 4 p-(Al0.7 Ga0
．． 3) 0.5 In0.5 P cladding layer 5 p-Ga0.5 In0.5 P layer 6
Al0.5 In0.5 P buried layer 7 p
-GaAs layer 8 P electrode 9 N electrode 10 MQB layer

Claims (1)

[Claims] 1. A laser active region into which current is injected in a stripe pattern, consisting of two types of semiconductor ultra-thin film layers having different energy gaps formed alternately, and the total thickness of the ultra-thin film layers being The multilayer ultra-thin film layer, in which the phase difference between the electrons incident on the ultra-thin film layer and the reflected electrons is approximately an odd multiple of π, and the thickness is less than that at which electron coherence is maintained, at least the stripe-shaped active region. A semiconductor laser characterized in that its side surfaces are coated.