Coherent light generators – Particular resonant cavity – Distributed feedback
Patent
1995-06-05
1996-09-10
Davie, James W.
Coherent light generators
Particular resonant cavity
Distributed feedback
372 46, H01S 319
Patent
active
055552552
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-emitting laser diode having a particularly good directional characteristic with utilization of the excitation of surface plasmon polaritons.
DESCRIPTION OF THE RELATED ART
A surface-emitting, radiation-producing semiconductor component, which is operated by means of excitation of surface plasmon polaritons, is described in European Patent Document EP-A-0 442 002. This component can be configured, in particular, as a laser diode. The structure is based on an emission mechanism by means of excitation and emission of surface plasmon polaritons, these being transverse electrical (TE) or transverse magnetic (TM) surface modes, which can propagate at the interface between two different media. With a suitable periodic structure of the interface, these modes can be excited using electromagnetic waves. The properties of light-emitting diodes, in particular laser diodes, can be improved using this emission mechanism. Loss mechanisms, which appear in conventional light-emitting components and limit the efficiency, can thus be avoided, at the same time the line width being considerably reduced and the external quantum yield being drastically increased. Directed radiation with a defined polarization can be achieved with a beam divergence of less than 6.degree.. In this case, a spatial periodic structure of the surface of the semiconductor material, that is to say the semiconductor surface facing away from a substrate over which there is growth, and a thin metal film applied thereto are essential for the design of this structure. The surface modes are excited at the surface, facing away from the semiconductor material, of this metal film, with the result that light is radiated in a directed manner from the surface. The polarization direction results from the direction of the periodic arrangement of the surface unevennesses.
SUMMARY OF THE INVENTION
It is the object of the present invention to specify an improved surface-emitting laser diode having intense beam focusing and an adjustable radiation direction.
This and other objects and advantages of the invention are achieved by means of the laser diode made of semiconductor material with an active layer and with contacts for applying an operating current, semiconductor material is provided with a spatial periodic structure, spatial periodic structure, of the surface, each period of the spatial periodic structure, the minimum distance of the metal film from the active layer and the thickness of the metal film are dimensioned such that, during operation of the laser diode, surface modes are excited at the surface, facing away from the active layer, of the metal film by photons produced in the active layer, and present as a layer or as a layer sequence on the side facing away from the spatial periodic structure of the active layer. Further refinements of the invention are characterized in that a further reflector arrangement is present between the active layer and the metal film.
The vertical resonator is bounded by the reflector arrangement and by the metal film in a preferred embodiment. The active layer is preferably arranged between contact layers which adjoin said active layer vertically with respect to the layer plane, and the spatial periodic structure is formed in the surface of a covering layer which is present between one of said contact layers and the metal film. The metal film may be applied in a recess of a contact. The metal film also forms a contact.
The laser diode according to the invention uses a layer structure, as is fundamentally known from conventional surface-emitting laser diodes having a vertical resonator. This structure is modified such that the radiation of light can take place by excitation of surface modes.
BRIEF DESCRIPTION OF THE DRAWINGS
There follows a description of the laser diode according to the invention using FIGS. 1 and 2, which each show an embodiment in an oblique sectional view.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIM
REFERENCES:
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patent: 5255278 (1993-10-01), Yamanaka
Y. Suematsu et al., "Advanced Semiconductor Lasers", Proceedings of the IEEE, vol. 80, No. 3, Mar. 1992, pp. 383-397.
E. Gornik et al., "Surface Plasmon Enhanced Light Emission in GaAs/AlGaAs Light Emitting Diodes", Proceedings SPIE, vol. 1362 Physical Concepts of Materials for Novel Optoelectronic Device Applications II: Device Physics and Applications (Oct., 1990), pp. 1-13.
Japanese Abstract, "Semiconductor Light Generator", JP 60-123084, vol. 9, No. 280 (E-356) (2003) Nov. 8, 1985.
Gornik Erich
Kock Anton
Davie James W.
Siemens Aktiengesellschaft
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