High resolution EL2 and resistivity topography of SI GaAs wafers

The mesoscopic inhomogeneity of LEC grown semi-insulating (SI) GaAs wafers has been investigated with EL2° absorption topography (EAT), photoluminescence topography (PLT), point contact topography (PCT) and contactless resistivity mapping (COREMA). Significant progress with respect to sensitivity of EAT and lateral resolution of COREMA has been achieved. High resolution topograms of wafers cut from ingots subject to standard and modified annealing procedures are presented. Direct comparison of EL2° and resistivity topograms reveals significant differences in the mesoscopic contrast and a contrast reversal for modified annealing. These observations can be explained very satisfactorily by assuming mesoscopic inhomogeneity of the intrinsic acceptor concentration which is modified during annealing. A model involving generation of Ga vacancies by dissolution of As_Ga antisites and gettering of the interstitial As at precipitates is presented and discussed