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Improving the Metallurgical Quality of Semiconductors

IP.com Disclosure Number: IPCOM000074652D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Chicotka, RJ: AUTHOR [+2]

Abstract

Generally, semiconductor crystals grown by the Czochralski technique are not suitable for PN junction fabrication because of their poor metallurgical quality. Usually, they are overlaid by one or more epitaxial layers in which the junction is made. A technique is described for improving the quality of such crystals and for reducing the number of steps required in using them.

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Improving the Metallurgical Quality of Semiconductors

Generally, semiconductor crystals grown by the Czochralski technique are not suitable for PN junction fabrication because of their poor metallurgical quality. Usually, they are overlaid by one or more epitaxial layers in which the junction is made. A technique is described for improving the quality of such crystals and for reducing the number of steps required in using them.

Referring to the drawing, the wafer is RF heated in a graphite or other susceptor to a point just short of the melting point, as determined by experiment. If the semiconductor is one that decomposes on melting with the loss of a volatile component, e.g., GaAs or GaP, an amount of that component is weighed into the capsule to provide the appropriate pressure to prevent decomposition. A commercially available radiation source of high-intensity light is focused onto the surface until superficial melting occurs. The power of the radiation source is then slowly reduced so the liquid layer freezes epitaxially onto the unmelted portion of the wafer. This layer is ""epitaxially'' grown and is substantially free of the strain, striae, and chemical inhomogeneities that are characteristic of the original Czochralski wafer. Therefore, a single epitaxial layer can be used for the formation of an active PN junction. Alternatively, a diffused junction can be made with the appropriate diffusant. Production of Red-emitting GaP Electroluminescent Diodes

Red-emitting Zn-O doped GaP diodes are made by a multistep procedure starting from "production grade" Czochralski grown GaP crystals. Red-emitting GaP electroluminescent diodes are double-doped with Zn and O on the p side of the junction and with a donor such as Te on the n-side. The efficiency of these diodes is strongly dependent on the manner of preparation. The best junctions are usually made by depositing a liquid phase epitaxial layer onto a single-crystal solution grown platelet substrate. However, for economy and efficiency of production it is desirable to use a Czochralski grown crystal for the substrate. This results in poor quality diode...