JPS62265786A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To produce a semiconductor laser in high luminous intensity at low oscillation threshold value current by a method wherein an active layer is composed of multiple quantum well structure while the peripheral parts of light emitting part of active layer is impressed with voltage by voltage impressing electrodes through the intermediary of insulating film on the growing surface side to reduce the refractive index of the well structure. CONSTITUTION:A part corresponding to an active layer 3 is composed of a multiple quantum well structure repeatedly laminated with barrier layers (A layers) and well layers(B layers) as well as peripheral parts excluding the central light emitting part to be impressed with an electric field. When the multiple quantum well structure is impressed with the electric field in the thickness direction, the refractive index thereof is reduced. The active layer 3 emits recoupled light by flowing current from a P side electrode 7 to an N side electrode 8 to laser-oscillate by the light resonance between the electrode 7 and a reflecting film 9 further to pick up the light transmitting the reflecting film 9 as output laser beams. When voltage is impressed upon the circuit between electrode 6 and 8, an electric field is made on the part excluding the central part of active layer 3 to reduce the refractive index confining the laser beams within the central part of active layer 3. Through these procedures, a refractive index waveguide type surface light emitting laser oscillating at low threshold value current is produced by one time crystal growth to emit laser beams in high luminous intensity at the central part of active layer 3.

Description

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor laser, and more particularly to a surface emitting type semiconductor laser constructed from a ■-V group semiconductor.

As an example of a conventional surface-emitting semiconductor laser, IEEE
Journal of QuantuIIIElect
ronics, Vol, QE-21°No, 8. J
une 1985. There is one shown in pp8B3-868. A schematic cross-sectional view of this surface-emitting semiconductor laser is shown in FIG. 3, with only the portions relevant to the present invention taken out.

Here, 21 is an n-type GaAs substrate with a hole for light extraction, 22 is an n-type AfIC, a As clad
LX layer, 23 is p-type GaAs active layer, 24 is p-type A (.

GaAs cladding layer, 25 is an insulating film, 26 is a p-side-y electrode, and 27 is an n (llll electrode). P-side type hi2 [i to n (
When a current is passed through the llll+ electrode 27, as a result, the active layer 2
Recombination light emission is caused at the center of the laser beam 3, and reflection is repeated on the upper and lower surfaces, resulting in laser oscillation. However, in such a conventional structure, since it is a gain-guided laser that uses current injection, the lateral optical confinement effect is weak and the oscillation threshold current is high, and the emission intensity in the center is weak or tends to become multiple spots. There was a drawback.

Summary of the Invention - Target This invention was made in response to these conventional problems, and the active layer has a quantum well structure.

The purpose of the present invention is to apply an electric field to areas other than the light-emitting part to lower the refractive index, thereby making it a refractive index waveguide type, and to solve the above-mentioned problems.

Structure and Effect In this invention, the part corresponding to the active layer is a so-called barrier layer (layer A) having a large energy gap.
It has a multi-quantum well structure in which so-called well layers (B layers), which have a smaller energy gap than the A layer that defines the actual emission wavelength, are repeatedly laminated, and an electric field can be applied to the surrounding areas other than the central light emitting part. is taking. It is known that when an electric field υ11 is applied to a multi-quantum well structure in its thickness direction, its refractive index decreases. By applying an electric field to the surrounding area other than the central light emitting part, it is possible to create a refractive index difference sufficient to confine light between the central light emitting part and its surroundings.

By injecting a current into the central portion, a refractive index guided surface emitting semiconductor laser can be formed.

In this way, a single-spot surface-emitting semiconductor laser that oscillates with a low threshold current and has high emission intensity at the center is realized.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a perspective cross-sectional view of the first embodiment, which has a so-called ballad structure. An n-type Aj on an n-type GaAs story fMI with a hole for light extraction directed downward:
A GaAs cladding layer 2 is formed xL-x, and an A layer GaAs(Ay
ly-y layer) and AI Ga As (B layer)
The active layer 3 is formed of a multi-quantum well consisting of a l-z layer thin film. On this active layer 3 is a p-type AI Gal.

An As cladding layer 4 is provided 2 and an n-side electrode 7 is provided at the center thereof.
is attached. P-type cladding layer 4-1. A voltage applying electrode 6 is formed with an insulating film 5 in between except for the central electrode 7 . An n-side electrode 8 is formed on the lower surface of the n-type LI[1, and a reflective film 9 is formed on the laser beam emitting part at the center of the lower surface of the cladding layer 2.

Here, the Aj2 composition ratios X and W of the cladding layers 2 and 4 are selected so that they are transparent to the emission wavelength of the active layer and have carrier confinement or Rf capability.

By passing a current from the n-side electrode 7 to the n-side electrode 8, light is recombined in the active layer 3, and the light is transmitted to the electrode 7 and the reflective film 9.
The laser oscillates due to resonance between the two, and the light transmitted through the first reflective film 9 is extracted as an output laser beam. When a voltage is applied between the electrodes 6 and 8, an electric field is applied to the active layer 3 except for the central part, and the refractive index thereof decreases. As a result, the laser light is confined in the center of the active layer 3 due to this refractive index difference, resulting in a refractive index guided laser.

FIG. 2 shows a second embodiment. Are the parts made of the same material as the first embodiment shown in Fig. 1 the same? ] Number is attached. No hole for light extraction is made in the substrate 1, and the n-side electrode 8 is formed on the entire lower surface of the substrate 1. Further, the n-side electrode 7 is formed in a ring shape. Under the n-type cladding 2, n-type A4 Ga As (C layer) and n! ! α 1-α A layer 2 Ga As (D layer) as active layer 3 emission wave β
λ/(4n c ) and λ/(4nD
) (where n and nD are the refractive indices of the C layer and D layer, respectively).
is provided. In this implementation 1j, the current injected from the ring-shaped electrode 7 toward the electrode 8 causes recombination light emission in the active layer 3, and this light resonates between the upper surface and the reflective film 10, and the Laser light is emitted from the central opening of the ring-shaped electrode 7. Electrodes 6 and 8 as in the first embodiment
Refractive index guiding can be achieved by applying a voltage between.

As described above, according to the present invention, a constant refractive index surface emitting laser that oscillates with a low threshold current can be created by one crystal growth. Moreover, by employing a refractive 4-waveguide structure, an li-spot laser beam with a strong emission intensity can be obtained at the center.

In the above example, A A G a A s /
Although GaAs-based lasers are mentioned, InP
The present invention is applicable not only to the Ga1nAsP/InP system using the radix, but also to all ■-■ group semiconductors.

Furthermore, the conductivity types n and p may all be reversed.

[Brief explanation of drawings]

FIG. 1 is a center sectional perspective view showing a first embodiment of the invention, and FIG. 2 is a center sectional perspective view showing a second embodiment of the invention. FIG. 3 is a central sectional perspective view showing a conventional example. 1--- n-GaAs substrate. 2- n -A J G a A s 11 layers. 3...Multiple quantum well active layer. 4--- p -A J G a A s 11th layer. 5... Insulating film, 6... Voltage application electrode. 7.8... Electrode, 9... Output side reflective film. 10...Multilayer reflective film. that's all

Claims (1)

[Claims] In a III-V group surface emitting semiconductor laser, the active layer has a multi-quantum well structure, and the electrode on the growth surface side is divided into an electrode for current injection and an electrode for voltage application via an insulating film around it, A semiconductor laser in which a voltage is applied around the light emitting part of the active layer using the voltage applying electrode to lower the refractive index, thereby creating an optical waveguide structure based on the difference in refractive index.