Spatially resolved study of dislocations in Si-doped LEC GaAs by DSL, PL and EBIC

Abstract

Three high-spatial-resolution methods, namely DSL (dilute Sirtl with light) photoetching, electron-beam-induced current (EBIC) and photoluminescence (PL), were used to study GS defects (grown-in dislocations which have moved from their original position leaving behind a Cottrell atmosphere and a trace) in Si-doped GaAs crystals grown from Ga-rich melts by the LEC method. A peculiar behaviour of these defects during DSL photoetching was revealed by interference contrast microscopy and surface profiling of the local etch rates: the start and end points of the GS defects were etched more quickly and the trace more slowly than the defect-free matrix. EBIC measurements showed a decrease in the net ionised impurity concentration at the Cottrell atmospheres but were ineffective in determining any compositional changes at the traces of the GS dislocations. PL mapping showed all components of the defects as well as remarkable spectral shifts at their different parts. On the basis of these results and previous data a model of the point defect equilibrium within the Cottrell atmospheres is proposed. The possible mechanisms of movement of the dislocations are considered, taking into account three different processes: climb, glide and climb/glide. It is argued that antisite AsGa defects (or related complexes) are formed during movement of the dislocations independently of the deviation from stoichiometry.