Infrared absorption of mixed silicon isotope pairs in gallium arsenide

Abstract

The infrared absorption of GaAs doped with ²⁸Si, ³⁰Si, or ²⁸Si + ³⁰Si and compensated by ⁶Li diffusion or electron irradiation is reported. Isotopic shifts close to those predicted from local‐mode theory are observed for all the silicon defect bands in ³⁰Si‐doped GaAs from frequencies previously reported for ²⁸Si‐doped material. a new band is observed at 456 cm⁻¹ for the sample containing both ²⁸Si and ³⁰Si, and is attributed to (²⁸Si–³⁰Si) pairs. The frequency of the new band is in accord with simple theory, and its presence confirms the observation of the nearest‐neighbor silicon pairs. The results indicate, however, that the indentification of one of the three absorption bands previously attributed to the ²⁸Si pairs is questionable. The experimental result also indicates that an absorption band at 369 cm⁻¹ previously observed in electron‐irradiated samples in indeed due to a silicon‐related defect.