Development of a Free Carrier Absorption Measurement Instrument for Indium Phosphide and Gallium Arsenide

摘要

An effort to develop and evaluate a contactless method for determining the spatial variation of the free carrier concentration in compound semiconductor materials is discussed. The capability of performing such measurements is of particular importance because of the current interest in producing electronic grade wafers from the III-V and II-VI compounds. These materials (particularly the II-VI compounds) tend to be nonuniform due to preferential migration of one of the constituents in the neighborhood of growth defects. All semiconductors which are grown at some finite temperature will contain Frenkel and Schottky point defects; such defects in compounds tend to be of a preferential nature which results in slight deviations from stoichiometry. These deviations can result in significant variations in doping concetrations and type. Defects in the macrostructure such as twin lines, grain boundaries, inclusions and dislocation lines can produce stoichiometric gradations which will also result in doping variations. The ability to distinguish short range variations in free carrier concentration is an extremely valuable aid to the crystal grower in the development of a particular growth process. Infrared adsorption by free carriers in semiconductors was demonstrated.