Abstract
Slices of Cr- and Fe-doped LEC crystals of InP were studied by secondary electron (SE) and transmission cathodoluminescence (TCL) scanning electron microscopy. Growth striations, twins and, in the Cr-doped material, centres showing strong dot and halo contrast were seen. The twin boundaries were visible in TCL micrographs due to weak dot-and-halo (DAH) contrast at twinning dislocations so incoherent boundaries gave strong contrast and coherent twin interfaces gave contrast only at steps. The strong DAH contrast centres in InP: Cr had crystallographic forms in secondary electron SEM pictures and X-ray microanalysis showed high concentrations of Cr to be present. Weaker DAH contrast occurs at the (partial) twinning dislocations. Annealing InP: Cr at 500°C for 30 min did not produce any distinct change in the microstructure. There appeared to be two types of twin interface. Across most there was strong secondary electron channeling contrast but not across the few of the other type. Both types could be seen in TCL due to bright contrast at the dislocations along the boundary. Only weak, bright contrast was observed at twinning dislocations in InP: Fe and the absence of the gross DAH contrast centres makes it possible to study the TCL contrast properties of twins, twin interfaces and striations, which were obscured in InP: Cr.
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