Direct observation of fine structure in the concentration of the deep donor [EL2] and its correlation with dislocations in undoped, semi-insulating GaAs

Abstract

Spatial variations in resistivity, dislocation density and [EL2] concentration across {001}, and sometimes {110}, specimens from semi-insulating, undoped, liquid encapsulated Czochralski GaAs ingots have been measured. By using detection methods capable of high spatial resolution (∼100 μm) it has been shown that fine structure in the well known ‘‘M’’- or ‘‘W’’-shaped distributions of dislocation density and [EL2] across 〈110〉 diameters of {001} wafers occurs. A close correlation between complex dislocation substructures, revealed by etching methods, and [EL2] distributions, revealed by infrared (1 μm) absorption microscopy, has been confirmed. The implications both for processes involving dislocation interactions during ingot growth and for the electrical properties of the semi-insulating material are considered.