JP2702964B2 - Semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum well type semiconductor laser device oscillating in a band of 1.2 to 1.6 μm, and particularly to a semiconductor laser having a wide modulation band or a low threshold. Related to the element.

[Conventional technology]

Conventionally, as described in JP-A-62-025484, GaAlAs
In a GaAs / GaAs quantum well semiconductor laser, when the active layer or the barrier layers on both sides of the active layer, or both, are doped with impurities, it is known that the modulation band is greatly improved or the threshold current value is reduced. Had been. However, in this material system, stable laser oscillation is difficult in the 1.2 to 1.6 μm band in the wavelength region where the loss of the quartz fiber is small or in the 0.6 to 0.7 μm band in the visible region.

On the other hand, the quantum well type semiconductor laser in the 1.2 to 1.6 μm band is realized by an InGaAs / InP system or the like. For example, 44th edition of the 10th International Conference on Semiconductor Lasers (October 1986)
From page 45 to page 45 (10th.International Semiconductor Laser
Conference).

[Problems to be solved by the invention]

However, the above-mentioned prior art is the most suitable for optical communication, 1.2 to 1.6 μm.
In a quantum well semiconductor laser that maintains an m-band oscillation wavelength, the modulation band has not been improved and the threshold current value has not been reduced.

An object of the present invention is to provide a quantum well semiconductor laser having a wide modulation band or a low threshold current value for optical communication or visible light.

[Means for solving the problem]

The above object is achieved by forming a quantum well structure using a material that generates laser oscillation in a band of 1.2 to 1.6 μm and doping impurities into barrier layers located on both sides of the active layer. As materials, InGaAs is used for the active layer and InGaAs is used for the barrier layer.
GaAlAs are each suitable. Each composition is determined for a desired oscillation wavelength in consideration of the thickness of each layer.

[Action]

For the quantum well structure formed of the above materials, p
If the impurity of the type is doped at a density higher than the carrier density to be implanted, excess holes are generated in the active layer, the differential gain is improved, and the modulation band is expanded. Therefore, high-speed modulation of the semiconductor laser becomes possible. On the other hand, when the n-type impurity is doped at a density higher than the carrier density to be injected, excess electrons are generated in the active layer, and the induced absorption is reduced, so that the threshold current value is reduced. For this reason, a low current operation becomes possible.

As described above, according to the present invention, the oscillation wavelength is 1.2 to 1.6 μm.
At m, a significant performance improvement of the semiconductor laser is achieved. The injection carrier density required for normal laser oscillation is 5 × 10
^{Since 17} cm ^{−3 to} 2 × 10 ¹⁸ cm ⁻³ , the density of the impurity to be doped is preferably 1 × 10 ¹⁸ cm ⁻³ or more, and more preferably 4 × 10 ¹⁸ cm ⁻³ or more.

In the long wavelength band of 1.2 to 1.6 μm, oscillation does not occur unless a large number of carriers are injected into the cavity due to the Auger effect and absorption between valence bands. For this reason, the injected electrons are energetically spread, and the differential gain tends to decrease. However, according to the structure of the present invention, when a large number of holes are present in the well layer, oscillation is caused by a small number of electrons, so that the energy of electrons in the well layer can be reduced in spread and the differential gain can be greatly increased. To improve. This effect is due to the 0.8 μm band GaAs
Larger than lAs system. And when the differential gain increases,
The relaxation oscillation frequency increases and the speed is increased.

Also, in the long wavelength band, the optical output level for end face breakdown is GaAlAs
One order of magnitude greater than the system. When the light output is large, the relaxation oscillation frequency becomes large, so that a very high relaxation oscillation frequency can be obtained.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described with reference to FIG. An n-type InAlAs cladding layer 2 (thickness: 3 μm, Al composition: 0.2 μm) is formed on an n-type InP substrate 1 (thickness: 100 μm) by a molecular beam growth method.
45), and then undoped InGaAs active layer 3 (thickness: 10).
0Å, Ga composition 0.45), p-type InGaAlAs barrier layer 4 (thickness 100Å,
Ga composition 0.20, Al composition 0.25, Be dope) are alternately grown.
Thereafter, the p-type InAlAs cladding layer 5 (thickness 2 μm, Al composition 0.4
5), p-type InGaAs cap layer 6 (thickness 0.5 μm, Ga composition 0.45)
Grow. Next, the p-side electrode 7 and the n-side electrode 8 are formed by vapor deposition, and cut into elements. In this device, the barrier layer 4
When the impurity density doped into is 2 × 10 ¹⁹ cm ⁻³ ,
The relaxation oscillation frequency that determines the high-speed modulation limit is 30 GHz
As a result, a value twice or more as compared with the conventional quantum well laser not doped with impurities was obtained.

 The laser oscillation wavelength was 1.55 μm.

A second embodiment of the present invention will be described with reference to FIG. After the same multi-layer growth as in the first embodiment is performed, the region 9 is removed by chemical etching while leaving the element central portion in a mesa shape. Thereafter, the region 9 is filled with semi-insulating InP, or polyimide, or InP which has been insulated by ion implantation of protons, boron, or the like. Thereafter, an insulating film 10 is applied, and the p-side electrode 7 and the n-side electrode 8 are deposited and separated into elements.
In this element, the light distribution is confined in the mesa portion by the region 9 and the capacity of the region 9 is small, so that the frequency limit of high-speed modulation is improved. A value of 35 GHz or more was obtained as a frequency band until the modulation intensity decreased by 3 dB.

As described above, the case where the p-type impurity is doped into the barrier layer has been described. However, similar results were obtained by doping the active layer or doping a part of the barrier layer. Also, in the above description, the doping impurity was made p-type, and the high-speed modulation limit was examined.On the contrary, the doping impurity was made n-type such as Te, Se, Si, etc., and the threshold current density was examined. A reduction of less than 1/2 was achieved.

〔The invention's effect〕

According to the present invention, in the quantum well laser,
Laser oscillation is performed at a wavelength in the 1.6 μm band, and the high-speed modulation limit can be increased or the threshold current value can be reduced. The high-speed modulation limit is more than twice that of the conventional quantum well laser.
Regarding the threshold current value, a value of 1/2 or less is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a quantum well semiconductor laser according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a buried semiconductor laser according to a second embodiment of the present invention. 1 ... substrate, 2 ... clad layer, 3 ... active layer, 4 ...
Barrier layer, 5 ... clad layer, 6 ... cap layer, 8 ...
... Electrode, 9 ... Embedded area.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-190992 (JP, A) JP-A-62-2229990 (JP, A) JP-A-62-24844 (JP, A) JP-A-60-1990 94787 (JP, A) JP-A-1-241884 (JP, A) JP-A-1-205586 (JP, A)

Claims (1)

(57) [Claims] A light emitting region having a quantum well structure including an active layer having a thickness smaller than a wave packet of free electrons in a crystal and semiconductor layers formed on both sides of the active layer; ¹⁸ cm ^-3 are introduced more impurities, the active layer is made of InGaAs and the semiconductor layer InGaAlAs
A semiconductor laser device comprising: