RECOGNITION AND MAPPING OF MICRODEFECTS BY PHOTOETCHING, LASER-SCATTERING TOMOGRAPHY AND PHOTOLUMINESCENCE IN SI UNDOPED GAAS AFTER DIFFERENT INGOT-ANNEALING TREATMENTS

Three independent but complementary methods (DSL photoetching combined with etch rate profiling, spatially resolved PL and LST) were employed to study the distribution of microdefects and electrically active centres in commercially available SI undoped, LEC-grown GaAs after different ingot-annealing treatments. A one-to-one correlation was obtained on comparing the microscale distribution of decoration precipitates (DPs), matrix precipitates (MPs) and microdefects (MMs) by the DSL and LST methods. Clustering of MPS is also revealed by PL intensity profiling and photoetch rate measurements. Two types of matrix microdefects are distinguishable by DSL photoetching in samples after two-stage annealing. A high degree of homogeneity across the dislocation cells (after low-temperature and multiple annealing) was clearly revealed by a drastic decrease in the uniformity parameter (U) after DSL photoetching and by a significant decrease in the PL intensity measured at the cell walls with respect to the cell interiors. Using the present results and recent data from the literature, an explanation of phase transitions during ingot annealing is proposed. This is based on the assumption that the final properties and structures after annealing are the result of two competitive processes: (i) formation of decoration and matrix microdefects; (ii) generation of electrically active point defects (clusters), presumably EL2.