Analysis of Impurity Distribution in Homoepitaxial n on n+ Films of GaAs which Contain High-Resistivity Regions

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Abstract
The occurrence of a high‐resistivity region (i layer) at the interface of n‐type GaAs films on n+ GaAs substrates has been a recurring problem in the halide synthesis transport growth of these films for microwave devices. Consistent success in the elimination of an i layer in the doping profile has been achieved by deposition of an n+ epitaxial film substrate prior to growth of the active n film, however the nature and cause of the i layer has remained unknown. It has been proposed by others that the i layer is caused by the presence of an impurity in that region. Under this assumption, a new analytical tool, the Direct Image Mass Analyzer (DIMA, Bell & Howell/CEC) has been used to obtain depth impurity profiles of known impurities through five homoepitaxial n‐on‐n+ GaAs film samples. These samples differed in the type of dopants used in the film and substrate, and in the magnitude of the i layers. The data were compared with doping profiles, and an analysis of this comparison has led to the following conclusions: (1) The impurities that are present in these samples include Si, K, Li, C, Na, Fe, F, Cl, and Mn; (2) the presence of an i layer is correlated with the presence of a high concentration (∼1×1021/cm3) of silicon in the i layer region; and (3) the origin of the silicon is probably external to the sample. The hardware of the reactor is a likely source of silicon, and a mechanism is proposed for the transport of the silicon into the growing film.