KR100240641B1 - Semiconductor laser - Google Patents

Abstract

The present invention provides a GaAs quantum well having a (In, Ga) As center layer of ultrathin film compressively strained biaxially to oscillate a laser having high polarization and gain characteristics. A GaAs / (Al, Ga) As laser structure composed of an active layer. A single or multiple GaAs quantum well active layer is placed between the upper and lower (Al, Ga) As buffer layers, and is located in the center of each GaAs quantum well (In, Ga) As center layer. Causes compressive deformation due to lattice mismatch with the GaAs layer. Since the difference between the base butt energy of the hard and hollow holes confined in the GaAs well structure with the compression-modified (In, Ga) As center layer presented by the present invention is much larger than that of the single quantum well structure, this active layer structure The laser having oscillates in a transverse electromagnetic wave (TE) mode with high gain characteristics. The method using the compressive strained center wall layer of the present invention can be applied not only to GaAs / (Al, Ga) As lasers, but also to other lasers such as InGaAs / InGaAsP / InP.

Description

Semiconductor laser

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor lasers, and more particularly to GaAs / (Al, Ga) As quantum well semiconductor lasers having a (In, Ga) As center layer of compression-deformation ultrathin films.

Recently, thanks to technological developments such as molecular beam epitaxy, high-quality GaAs / (Al, Ga) As quantum well structures can be grown, and this semiconductor structure has been widely used for laser development near 800 nm wavelength. Semiconductor quantum well lasers are more constrained in the two-dimensional well potential wall layer that gives charges than lasers consisting of an active layer of agglomerate material, thereby increasing the intensity of the light transition between electrons and holes, as well as By quantizing the boutique energy, the state density function of the quantum state is changed to improve the gain characteristics of the laser. Currently known methods for GaAs / (Al, Ga) As quantum well lasers are those in which one or more GaAs quantum wells are composed of the active layer of the laser. The valence band quantum wells of GaAs / (Al, Ga) As are bound with bouts of heavy-holes and light-holes, and are grown on the [001] axis. Since the effective mass of the axial hollow hole is heavier than that of the hard hole, the baseband energy of the hollow hole in the quantum well made of this material is closer to the conduction band than that of the hard hole. As a result, the light transition between the conduction band and the valence transition band mainly occurs between the electrons of the conduction band and the mesopores of the valence band, and the laser oscillation based on the transition mainly has a transverse electric wave (TE) mode characteristic.

The above-described conventional semiconductor laser is a significant improvement over the laser having a gain layer of agglomerate in terms of gain characteristics, but as the temperature distribution rises, the energy distribution function of the charges moves toward higher energy, so that the conduction band base band and the hard hole The gain characteristics can be deteriorated due to effects such as spontanuous emission between the base butts or between the second and second bouts of the mesoporous basal butt. This problem can be solved by maximizing the difference between the basal energy of the heavy and light balls using wavefunction engineering to minimize the effects of the light balls.

Accordingly, the present invention proposes an active layer structure having high transverse electromagnetic wave (TE) polarization and gain characteristics in the fabrication of GaAs / (Al, Ga) As quantum well lasers, thereby making it possible to utilize semiconductors in optical, optical communication, and photovoltaic fields. The purpose is to provide a laser.

A semiconductor laser according to the present invention for achieving the above object is provided with a GaAs substrate, a p + dope GaAs layer formed on the substrate, the Al _y Ga _1-y As first buffer layer located on the GaAs layer, An active layer for laser oscillation formed on the first buffer layer, an Al _y Ga _1-y As second buffer layer formed on the active layer, and an n + doped GaAs layer formed on the second buffer layer. The active layer is characterized by consisting of a GaAs layer having a thickness of 5 to 20 nm and an In _x Ga _1-x As (x <1) ultra-thin layer having a thickness of 0.2 to 2 nm in the center thereof.

In addition, the semiconductor laser according to the present invention is characterized in that it is possible to form an active layer composed of a plurality of GaAs quantum wells separated by Al _z Ga _1-z As (z <y). However, each GaAs layer is characterized by having a 0.2 _x 2 nm thick In _x Ga _1-x As (x <1) ultrathin layer at the center thereof.

1 is an active layer structure diagram of a GaAs / (Al, Ga) As laser according to a first embodiment of the present invention.

2 is an active layer structure diagram of a GaAs / (Al, Ga) As laser according to a second embodiment of the present invention.

3 is an energy band structure diagram of a GaAs / (Al, Ga) As single quantum well.

4 is an energy band structure diagram of a GaAs / (Al, Ga) As quantum well having a (In, Ga) As center layer according to the present invention.

<Explanation of symbols on the main parts of the drawing>

1, 21: substrate 2, 22: first buffer layer

3, 23: p + doping layer 4, 24: quantum well layer and the first quantum well layer

5, 25: ultra thin layer and first ultra thin layer 6, 26: second buffer layer

7, 27: n + doping layer 28: wall layer

34: second quantum well layer 35: second ultra thin layer

A: active layer B: first active layer C: second active layer

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 is a structural diagram of a laser according to a first embodiment of the present invention. As shown, a p + dope GaAs layer 2 is formed on the GaAs substrate 1, and an Al _y Ga _1-y As (y <1) first buffer layer 3 is formed on the GaAs substrate 1. An active layer A for laser oscillation is formed on the first buffer layer 3.

The active layer A is formed of a GaAs quantum well layer 4 having a thickness of 5 to 20 nm and an In _x Ga _1-x As (x <1) ultra-thin layer 5 having a thickness of 0.2 to 2 nm at the center thereof. do. A second buffer layer 6 made of Al _y Ga _1-y As having the same composition as the first buffer layer 3 is formed on the active layer A. An n + GaAs layer 7 is formed on the second buffer layer 6.

2 is a schematic diagram of a laser according to a second embodiment of the present invention. As shown, a p + dope GaAs layer 22 is formed on the GaAs substrate 21 and an Al _y Ga _1-y As first buffer layer 23 is formed thereon. The first active layer B for laser oscillation is formed on the first buffer layer 23. The first active layer B is formed of a GaAs quantum well layer 24 having a thickness of 5 to 20 nm and an In _x Ga _1-x As (x <1) ultra-thin layer 25 having a thickness of 0.2 to 2 nm at the center thereof. Is done. On the first active layer B, a wall layer 28 made of Al _z Ga _1-z As (z <y) for separation from the second active layer C is formed. The second active layer C having the same structure as the first active layer B is formed on the wall layer 28. The second active layer is formed of a GaAs quantum well layer 34 having a thickness of 5 to 20 nm and an In _x Ga _1-x As (x <1) ultra-thin layer 35 having a thickness of 0.2 to 2 nm in the center thereof. An Al _y Ga _1-y As second buffer layer 26 having the same composition as the first buffer layer 23 is formed on the second active layer C. An n + GaAs layer 27 is formed on the second buffer layer 26.

Although FIG. 2 is limited to a laser structure having a first active layer (B) and a second active layer (C), the present invention also includes two or more active layers.

3 is an energy band structure diagram of a GaAs / (Al, Ga) As single quantum well in general. This takes into account the case of GaAs / (Al, Ga) As quantum wells without an ultrathin (In, Ga) As center layer. As shown, the mesopores and the meridian balls differ in the ground state energy bound to the quantum wells because of the difference in their effective mass. In other words, because the effective mass of the mesopores on the quantum well growth axis is heavier than the yangyanggong, the ground state boutique energy is closer to the conduction band than that of the yangyanggong. In this case, the main factor of the laser oscillation is the stimulate emission between the electron and the hollow hole bouncy, and thus has the characteristic of transverse electric wave (TE) mode. However, since the energy difference is not so large compared to the Boltzman energy of about 25 meV corresponding to room temperature, the gain characteristic is reduced due to the automatic emission by the yangtung hole base booty when laser oscillation at room temperature.

In order to solve the above disadvantages, the energy band structure of the laser structure according to the present invention as shown in FIG. 4 is presented. As shown, in the case of GaAs / (Al, Ga) As quantum wells with the (In, Ga) As ultra-thin layer added at the center, the band edge of the hard hole of the (In, Ga) As layer that is compressively strained Is on the side away from the conduction band, compared to the edge of the unmodified GaAs band, and the mesopores tend to be opposite to the conduction band, and are placed close to the conduction band. In GaAs / (Al, Ga) As quantum wells with a compressively strained (In, Ga) As center layer, the mesopore edge potential potential of the (In, Ga) As center layer acts as a well potential but that of the hard hole As the potential acts as a potential, the mesoporous basal buttress closes to the conduction band, while the mesoporous basal buttress energy tends to be reversed. Very increased. On the other hand, the basal bouncy wave function of the mesopore is symmetrical with respect to the center of the GaAs well layer, but the next higher bouncy wave function of the mesohole is antisymmetric, so The difference between the basal and second-order energy changes in the mid-hole is also greatly increased.

Therefore, the GaAs / (Al, Ga) As laser using the structure shown in FIGS. 1 and 2 and the energy band structure of FIG. 4 will have the TE-mode oscillation with improved gain at room temperature.

As described above, a GaAs quantum well having an ultra-thin (In, Ga) As center layer according to the present invention and a semiconductor laser having an active layer composed of a plurality thereof obtain an improved gain at room temperature, thereby providing optical, optical communication, and optical It is an excellent effect that can be used as a key component in computer and related fields.

Claims (6)

Provided GaAs substrate, A p + GaAs doping layer formed on the GaAs substrate, A first buffer layer composed of Al _y Ga _1-y As (y <1) on the p + GaAs doping layer, An active layer composed of a double GaAs quantum well layer having an In _x Ga _1-x As (x <1) center layer of an ultra-thin film compression-deformed on the first buffer layer; A second buffer layer formed of Al _y Ga _1-y As on the active layer; And a n + GaAs doping layer formed on the second buffer layer. The semiconductor laser according to claim 1, wherein the GaAs quantum well layer is 5 to 20 nm thick. The semiconductor laser according to claim 1, wherein the ultra-thin In _x Ga _1-x As (x &lt; 1) center layer is 0.2 to 2 nm thick. 2. The semiconductor laser according to claim 1, wherein the butt energy of the mesopores and the mesopores of the GaAs quantum well layer is adjusted by the In _x Ga _1-x As (x <1) center layer of the ultra-thin film. Provided GaAs substrate, A p + GaAs doping layer formed on the GaAs substrate, A first buffer layer composed of Al _y Ga _1-y As (y <1) on the p + GaAs doping layer, A first active layer composed of a double GaAs quantum well layer having a compression-modified ultra-thin In _x Ga _1-x As (x <1) center layer on the first buffer layer, A wall layer composed of Al _z Ga _1-z As (z <y) on the first active layer, A second active layer comprising a double GaAs quantum well layer having a compression-modified ultra-thin In _x Ga _1-x As center layer on the wall layer; A second buffer layer formed of Al _y Ga _1-y As on the second active layer; And a n + GaAs doping layer formed on the second buffer layer. 6. The semiconductor laser according to claim 5, wherein the first active layer or the second active layer is separated by a wall layer composed of Al _z Ga _1-z As (z &lt; y).

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