Process for thermal gradient zone melting utilizing a guard ring radiation coating

Claim 1

An improvement in the processing of a body of semiconductor material by thermal gradient zone melting comprising the steps of: (a) selecting a body of semiconductor material having a preferred crystal structure, a preferred type of conductivity, a preferred level of resistivity, two major opposed surfaces being, respectively, the top and bottom surfaces of the body, at least one of the major surfaces having a preferred planar crystal orientation which is one selected from the group consisting of (100), (110) and (111), and a vertical axis substantially aligned with a first preferred crystal axis of the material of the body; (b) forming a layer of a material suitable for absorbing or for re-radiating a predetermined range of wavelength of the most intense portion of the radiation spectrum impinging thereupon on at least one of the two major opposed surfaces, the layer having a predetermined thickness, t, expressed by the following general equation: ##EQU8## wherein n= any positive integer greater than zero, λ = the wavelength in vacuum of the most intense portion of the radiation spectrum impinging upon the layer of material, and N= the index of refraction of the material; (c) shaping the first layer of material to conform to a particular configuration and to cover a predetermined surface area of the major surface of the body on which it is disposed; (d) exposing the processed body to a source of radiant energy; (e) absorbing the predetermined range of wavelength of the most intense portion of the radiation spectrum in the first layer, and (f) increasing the heat flow lines through a predetermined portion of the material of the body to enhance the migration of a metal-rich semiconductor material therethrough by thermal gradient zone melting.