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Light Emitting Diode Optical Probe for Epitaxial Film Characterization

IP.com Disclosure Number: IPCOM000076277D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Edmonds, HD: AUTHOR

Abstract

This apparatus is useful for characterizing epitaxial semiconductor films and detecting imperfections particularly in III-V compounds.

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Light Emitting Diode Optical Probe for Epitaxial Film Characterization

This apparatus is useful for characterizing epitaxial semiconductor films and detecting imperfections particularly in III-V compounds.

The well-known techniques of absorption spectroscopy can be used to measure absorption coefficients. This is done easily and accurately for semiconductor materials, but requires a relatively large carefully prepared sample. Often an epitaxial layer is grown on a substrate and the bandgap of the grown layer is wider than the bandgap of the substrate, for example, GaAs(1- x)P(x) or Al(x)Ga(1-x)As on GaAs. Radiation normally transmitted by the epitaxial layer is heavily absorbed by the substrate. Therefore the substrate would have to be removed in order to measure the absorption coefficient by this technique. This is not possible for thin epitaxial films e. g. thickness < 25 mu.

This apparatus provides a convenient way to examine some of the properties of an epitaxial film without removing the substrate. It can also be used as a quality check to quickly examine wafers before they are processed. The procedure for making the measurement of interest involves cleaving a small bar from the wafer on which the epitaxial layer is grown, imaging the light from a light-emitting diode in the epitaxial layer by an optical system, and either observing or characterizing the image with optical measurements.

The arrangement illustrated includes a light-emitting diode 1 mounted for end emission from the cleaved surface, microscope 2 having a first lens 3 to collimate the light from the diode, and a second lens 4 for...