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Source Shaping in the Fabrication of Semiconductor Light Emitting Diodes by Molecular Beam Epitaxy

IP.com Disclosure Number: IPCOM000077140D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Chang, LL: AUTHOR [+2]

Abstract

The performance of immersed semiconductor photo-sources depends on effects such as absorption and total internal reflection. The photometric figures of merit in terms of efficiency, radiance, or radiance intensity, therefore, are strongly dependent on the source geometry. A specific shape of geometry would result in a specific optimum figure of merit required for different applications such as display. data retrieval and optically-coupled microcircuits. For example, a hemispherical source would give a maximum efficiency; while a paraboloidal source, a maximum radiant intensity.

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Source Shaping in the Fabrication of Semiconductor Light Emitting Diodes by Molecular Beam Epitaxy

The performance of immersed semiconductor photo-sources depends on effects such as absorption and total internal reflection. The photometric figures of merit in terms of efficiency, radiance, or radiance intensity, therefore, are strongly dependent on the source geometry. A specific shape of geometry would result in a specific optimum figure of merit required for different applications such as display. data retrieval and optically-coupled microcircuits. For example, a hemispherical source would give a maximum efficiency; while a paraboloidal source, a maximum radiant intensity.

In conventional methods, desirable geometries are difficult to achieve, and usually a number of processing steps are involved including cutting, lapping, and etching. A simplified technique for source shaping by the incorporation of a movable mask during the process of growing the material by evaporation is as follows:

Fig. 1 shows schematically the pertinent parts of an apparatus for molecular beam evaporation. Included are a source, a substrate and a holed mask movable along the z-direction. Additional sources and masks can be added if required. By moving the mask toward the substrate, the area of deposition reduces. The final shape of the material grown is determined by the time- dependence of the mask movement. For example, assuming a constant rate of growth, a linear dependence would result in a cone, and a quadratic dependence, a paraboloid. Other shapes can also be achieved including those which are truncated. Typical materials for evaporation are GaAlAs or other compound and alloyed semiconductors. Source shaping can also be achieved by moving either the source or the substrate or in combin...