Semiconductor laser component

Details Semiconductor laser component Semiconductor laser component

1999-08-02

2001-09-04

Leung, Quyen P. (Department: 2881)

Coherent light generators

Particular active media

Semiconductor

C372S046012

Reexamination Certificate

active

06285697

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a unipolar semiconductor laser component, including a semiconductor body with a hetero-structure configuration, in particular an SCH (Separate Confinement Heterostructure) configuration, which is suitable for generating an electromagnetic radiation. In the configuration, an active layer sequence with a quantum well structure is provided between a first outer cover layer of a first conductivity type and a second outer cover layer of the first conductivity type above a semiconductor substrate. The electromagnetic radiation is generated within the quantum well structure (or active zone) when current flows through the semiconductor body. The cover layers have a lower index of refraction than the active layer sequence, and as a result an optical wave being generated during operation is confined between the cover layers. A laser diode is described in a paper entitled “Carrier and Photon Dynamics in Transversally Asymmetric High-Speed AlGaInAs/InP MQW Lasers”, by H. Hillmer, A. Greiner, F. Steinhagen, H. Burkhard, R. Loesch, W. Schlapp and T. Kuhn, in Physics and Simulation of Optoelectronic Devices IV, SPIE, Vol. 2693 (1996), pp. 352-368. In that laser diode, an n-conducting cover layer of InP and over that an active layer sequence formed of InGaAs/AlInGaAs and a further cover layer of p-conducting InAlAs, are applied over a semiconductor substrate of semi-isolating or n-conducting InP. The active zone is formed of InGaAs multiple quantum wells (MQWs) which are embedded in AlInGaAs barriers and AlInGaAs waveguide layers. The AlInGaAs waveguide layers are both p-conducting, but at p=5*10
17
cm
−3
, have lesser doping than the cover layers of InP (where n=2*10
18
cm
−3
) or InAlAs (where p=2*10
18
cm
−3
). The configuration disclosed by Hillmer et al is a so-called separate confinement heterostructure (SCH), in which electrons in holes are injected into an active zone through a pn junction which is formed substantially of the cover layers, in that case n-InP and p-InAlAs. The optical wave being generated is carried, regardless of the charge carrier confinement in the quantum wells, through the waveguide, which is surrounded by the cover layers with the lower index of refraction. In that special case, the active MQW zone is not symmetrical, or in other words placed centrally in the waveguide. The waveguide is shortened on the side toward the p-conducting cover layer, in order to speed up the transport of holes into the quantum well, since holes in principle have markedly lesser mobility than electrons. Improved modulability is thus attained, which is determined essentially by the transport of less mobile holes within the moderately doped waveguide and by the electron confinement in the MQW structure.
The basic structures of quantum well and MQW semiconductor lasers and of the SCH configuration are described, for instance, in a book entitled “Die physikalischen Grundlagen der LED's, Diodenlaser und pn-Photodioden” [The Physical Basis of LED's, Diode Lasers and pn-Photodiodes] by W. Buldau, in Halbleiter-Optoelektronik [Semiconductor Optoelectronics], Hanser-Verlag, Munich and Vienna, 1995, pp. 182-187, and are therefore not described in further detail herein.
In lasers based on the materials InGaAsP and AlInGaAs that have been tested thus far, the hole mobility in the waveguide layer is markedly less than the mobility of electrons.
In order to provide a high data transmission rate at wavelengths of 1.3 &mgr;m and 1.55 &mgr;m in the optical window of conventional glass fibers, a limitation to high-frequency modulability is presented by the drift transport of less-mobile holes into the quantum well and the electron confinement in the MQW structure.
Due to the aforementioned shortening of the waveguide layer on the p side, the transport length for holes in the waveguide can be shortened. However, the drift speed is determined by the electrical field applied and by the poor mobility.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor laser component, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which has improved operability in comparison with the above-described known semiconductor laser component and which, in particular, has improved high-frequency modulability at wavelengths in a range between 1.3 &mgr;m and 1.55 &mgr;m.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor laser component, comprising a semiconductor body having a heterostructure configuration suitable for generating an electromagnetic radiation, the heterostructure configuration including: a semiconductor substrate; a first outer cover layer of a first conductivity type disposed above the semiconductor substrate; a second outer cover layer of the first conductivity type disposed above the semiconductor substrate; an active zone layer sequence with a quantum well structure disposed between the first and second outer cover layers, for generating the electromagnetic radiation in the quantum well structure when current flows through the semiconductor body; and a charge carrier injector for accelerating charge carriers within an internal electrical field and thereby injecting the charge carriers rapidly into the active zone, the charge carrier injector having a first highly doped denatured transition layer (for instance n
+
or p
+
) of a second conductivity type opposite the first conductivity type and a second highly doped denatured transition layer (such as p
+
or n
+
) of the first conductivity type, disposed between the active layer sequence and the second outer cover layer, the second highly doped denatured transition layer disposed between the first highly doped denatured transition layer and the second outer cover layer.
The terms highly n-doped (or n
+
-doped) and highly p-doped (or p
+
-doped), or in other words denatured doping, are each advantageously understood to mean a dopant concentration of ≧10
17
cm
−3
.
The n
+
p
+
layer sequence acts as a “hole injector”, by which electrons near the active zone are converted into holes and are accelerated in the electrical field. Consequently, through the use of this n
+
p
+
layer sequence, which is polarized in reverse relative to the component, charge carriers within an internal electrical field are accelerated in the n
+
p
+
layer sequence and injected more quickly into the active zone. The n
+
p
+
layer sequence functions as a source for charge carriers inside the cover layers.
In the charge carrier injector, at the distance of one Debye length around the junction, a genuine reversal of the conductivity type occurs. In other words, the Fermi level is put in the conduction band by n-doping on one side of the diode, and holes pull the Fermi level into the valence band by p-doping on the opposite side (this is known as “denaturing”). Due to the very narrow space charge zone, which is only a few angstroms wide, between these regions of denatured doping in the charge carrier injector, reverse polarity can lead to interband tunnels of electrons out of the valence band of the p-doped semiconductor in conditions of the conduction band of the n-doped semiconductor, as a result of which holes are created in the p-doped region.
In accordance with another feature of the invention, a barrier layer of an arbitrary conductivity type that is lesser doped than the transition layers is disposed between the first highly doped denatured transition layer and the second highly doped denatured transition layer. This barrier layer may form a barrier for electrons that extend past the active zone.
In accordance with a further feature of the invention, a thin barrier layer for electrons that has lesser doping than the transition layers is disposed between the first highly doped denatured transit

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