Abstract
In this work undoped semi-insulating (SI) GaAs grown by vertical gradient freeze and liquid encapsulated Czochralski methods was studied by near-infrared absorption (NIRA), thermally stimulated current (TSC) and positron annihilation techniques. The positron experiments reveal both gallium and arsenic vacancies, as well as gallium and arsenic antisites, in the samples. By comparing the results from the TSC and positron measurements, the following relations are found in the defect concentrations: trap T2 correlates with the arsenic antisite and trap T5 with the arsenic vacancy. The ionized fraction of the arsenic-antisite-related EL2 defect is obtained from NIRA measurements. The positive charge of these ionized EL2 defects correlates with the net negative charge, 3[VGa3−]+2[GaAs2−]−[VAs+], related to the gallium vacancies and antisites and arsenic vacancies detected in positron measurements. The intrinsic defects may thus contribute significantly to the electrical compensation in SI GaAs.
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