JPS60235492A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve luminous efficiency, and to lower oscillation value currents by forming an active layer held by clad layers in quantum well type potential structure and flowing electrons and holes in the direction parallel with boundary surfaces among the clad layers and the active layer. CONSTITUTION:When well layers 50 are made shorter than the de Broglie wavelength of carriers in a semiconductor, injecting carrier density required for laser oscillation reduces due to a quantum size effect, and oscillation value currents are minimized largely. When differences among the band gaps of barrier layers 9 and the well layers 50 are formed in large values in order to inject carriers in parallel with boundary surfaces among clad layers 4, 6 and an active layer 5, current injection efficiency is not deteriorated, couplings among the well layers can be reduced sufficiently, a quantum level can be made sufficiently higher than the band gaps of the well layers without increasing oscillation value currents, and laser oscillation at short wavelengths is facilitated. Since quantum well type potential structure is formed, gain spectral width is reduced to one several-th of conventional devices, thus resulting in easy single longitudinal mode oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improving the performance of a semiconductor laser, particularly a lateral current injection type semiconductor laser.

[Prior art]

A conventional device of this type is shown in FIG.

FIG. 1 is a cross-sectional view showing the main parts of a conventional semiconductor laser. In the figure, (1) is a p@ electrode, (2) is an n-side electrode, and (3) is an n-type cap layer made of, for example, GaAs. . (4) is the n-type cladding layer A/xGa + -xAs
It becomes more. 15) is an n-type active layer with ApyGa + −
yAs (y(x) There is.

(6) is an n-type cladding layer, and like cladding layer (4), A
/xGa + -xAs, (7) is a semi-insulating substrate made of GaAs, and (8) is a region (shaded area) made p-type by double diffusion of zinc (Zn).

(a) is the intersection region between the active layer 15) and the region where the p-type concentration is lower than the region (8) formed by double diffusion;
Laser oscillation occurs from this region (801).

Next, the operation will be explained.

When a current is passed in the forward direction through the p-n junction from the p-side electrode (1) to the naut electrode (2), the active layer (5) and the cladding layer 14+
, +61, most of the current is concentrated only in the active layer 15) in the lateral direction, that is, in the cladding layer +
41, flows in a direction parallel to the interface between +61 and active @I51. At this time, radiative recombination of carriers occurs near the p-n junction of the active layer (5), that is, in the cross region (801). A resonator is formed in the striped active layer (5) sandwiched between the cleavage planes at both ends when the semiconductor laser is cut out, and the p-layer and n-layer are formed in the horizontal direction, and the cladding layer is formed in the vertical direction. 14i
(The active layer sandwiched between the layers 61 becomes a leading wave layer having a higher refractive index than the surroundings, trapping light and producing efficient laser oscillation.

In a conventional lateral current injection type semiconductor laser having such a configuration, the oscillation value current decreases in proportion to the decrease in the active layer thickness. However, when the active layer thickness is reduced to ~1oooA, the leakage of guided light to the cladding layer increases, and when the active layer thickness is further reduced, the value current increases, so the activity of conventional semiconductor lasers is Layer (5)
The layer thickness was set to about 1500A, and there was a lower limit to the current value.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the active layer sandwiched between cladding layers is formed with a quantum well type potential structure, and the interface between the cladding layer and the active layer is The object of the present invention is to provide a semiconductor laser that can increase the luminous efficiency and lower the oscillation value current than the conventional laser by causing electrons and holes to flow in parallel directions.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

2(a) and 2(b) are a sectional view and an enlarged sectional view of the vicinity of the active layer of a conventional semiconductor laser, respectively, and FIGS. 3(a) and 3(6) are a sectional view of an active layer according to an embodiment of the present invention. FIG. 2 is a diagram showing a duction band structure and an enlarged cross-sectional view of the vicinity of an active layer. In the figure, (c) is the enlarged area, and the active layer (5)
Enlarge the vicinity.

The arrow (g) indicates the energy level (q indicates the thickness direction. ω is a well layer with a narrower band gap than the cladding layer +41 +61, and is the part where the injected carriers accumulate. (9) is the well layer This is a barrier layer with a wider bandgap than the layer (2).The active layer (5) is composed of the well layer (2) and the barrier layer (9), and has a multi-quantum well type potential structure.The well layer haze and the barrier layer (9) ) are each less than 1 Å thick, and each number is optimized depending on the degree of optical confinement in the thickness direction, but the total thickness of the well layer group and barrier layer (9) is approximately 100 Å. As for the material of each layer, for example, the well layer (5o) is made of n-type GaAs, and the barrier layer (9) and cladding layer 14+ +6) are made of n-type A/Ga.
A region t is formed of As, and a region t is formed in order to pass a current through the active layer (5).
A p-type dopant is diffused or ion-implanted into the s+ layer to form a pn junction in the lateral direction, resulting in a lateral current injection type semiconductor laser.

Further, the active layer (5) may be formed of a so-called modulation doped structure in which the well layer group is non-doped and the barrier layer is n-type doped.

In the semiconductor laser having the above configuration, the well layer (
When 5ol becomes shorter than the de Broglie wavelength of carriers (electrons, holes) in the semiconductor, the injection carrier density necessary for laser oscillation decreases due to the quantum size effect, and the oscillation value current decreases significantly. Furthermore, in the above-mentioned lateral current injection semiconductor laser, the carriers are injected parallel to the interface between the cladding layer and the active layer, so the current injection efficiency does not decrease even if the band gap difference between the barrier layer and the well layer is large. . Therefore, since the coupling between the well layers can be made sufficiently small, the quantum level can be sufficiently raised above the bandgap of the well layers without increasing the value current, and laser oscillation at a short wavelength becomes easy. Furthermore, by using a quantum well type potential structure, the gain spectrum width becomes a fraction of that of a conventional type, so that it has the characteristic of facilitating single-longitudinal mode oscillation.

In the above embodiment, a multi-quantum well structure was applied to the active layer region, but this was simplified and the active layer (well layer ω) was made into a single layer as shown in FIG. 4, resulting in a single-quantum well type potential structure. Good too. At this time, if the layer thickness is set to several hundred λ or less in order to produce a quantum size effect, the optical confinement becomes weak, so a light guide having a band gap between the cladding layer 14+ +6+ and the active layer (5) is placed on both sides of the active layer (5). A wave layer α is provided. In this case, the mixed crystal composition of the optical waveguide layer 00) is constant. Note that this leading wave layer opening 0) forms a part of the cladding @14+ +61, and separates the light wave and electron confinement effects.

Moreover, FIGS. 5(a) and 5(b) are diagrams showing the conduction band structure of the active layer and an enlarged sectional view of the vicinity of the active layer according to other embodiments of the present invention, respectively, and show the optical waveguide layer (10).
The composition of the mixed crystal has a parabolic slope. That is, the active layer (5) has a single-quantum well type potential structure, and on both sides of the active layer, there are optical waveguide layers (i) having a gradient in bandgap size between the cladding layer +41 +61 and the active layer (4). 0) to achieve optical confinement as the fourth
It can be made stronger than the case shown in the figure.

FIG. 6 shows another embodiment of the present invention, in which the active layer 51 has a multi-quantum well potential structure, and leading wave layers 00) are provided on both sides of the active layer 5 to generate light waves. It confines electrons.

〔Effect of the invention〕

As described above, according to the present invention, the active layer is formed with a quantum well type potential structure, and the grooves are formed so that the edges and holes flow in a direction parallel to the interface between the cladding layer and the active layer. This has the effect of making it possible to reduce the value current, etc., and obtaining a high-performance semiconductor laser.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the main parts of a conventional semiconductor laser, FIG. 2 is a cross-sectional view of a conventional semiconductor laser and an enlarged cross-sectional view of the vicinity of its active layer, and FIG. A diagram showing the conduction band structure of the layer and an enlarged sectional view of the vicinity of the active layer, FIGS. 4, 5, and 6 are diagrams showing the conduction band structure of the active layer according to other embodiments of the present invention. and an enlarged cross-sectional view of the vicinity of the active layer. +41, +61...Clad 1.151...Active layer, Cl0)...Optical waveguide layer In the drawings, the same reference numerals indicate the same - or equivalent parts. Agent: Masuo Oiwa, Figure 1, Figure 3, Figure 5, Figure 6. Relationship with the Ministry case 1-1 Representative of the applicant Hitoshi Katayama Department 4 Attorney 5 Column 6 for detailed explanation of the invention and brief explanation of drawings in the specification subject to amendment, Contents of amendment (1) In the specification, page 8, lines 12 to 18, "within the striped active layer (5) sandwiched between" is corrected to "1". (2) "Oscillation value" on page 8, line 20 of the same page "1 oscillation, 1 value"
Correct. (3) Correct "value current" in lines 8, 5, and 12 of page 4 to "threshold current", respectively. (4) Correct "active layer conduction" from page 4, line 20 to page 5, line 1 to read "around 1 active layer" (5)
"White A" on the 11th line of the page is corrected to "100 A". (6) In the same page, page 6, line 7, "oscillation value current" is corrected to "oscillation value electric current". , 7) On page 7, line 11, "conduction of the active layer" is corrected to "near the active layer." (8) Correct "oscillation value current" in line 7 of page 8 to "oscillation value current". (9) [Correct the conduction J of the active layer in lines 14 and 17 of page 8 to ``near the active layer,'' respectively. that's all

Claims (5)

[Claims] (1) The active layer sandwiched between cladding layers is formed with a quantum well type potential structure.1. A semiconductor laser configured to allow electrons and holes to flow in a direction parallel to an interface between the cladding layer and the active layer. (2) The semiconductor laser according to claim 1, wherein the quantum well type potential structure is a multi-quantum well type potential structure. (3) The semiconductor laser according to claim 1, wherein the quantum well type potential structure is a single quantum well type potential structure. (4) The semiconductor laser according to any one of claims 1 to 3, wherein a waveguide layer having a band gap intermediate between that of the cladding layer and the active layer is formed on both sides of the active layer. (5) The optical waveguide layer according to any one of claims 1 to 3, wherein an optical waveguide layer having a bandgap with a slope between the cladding layer and the active layer is formed on both sides of the active layer. semiconductor laser.