TEM INVESTIGATIONS OF DEFECTS IN UNDOPED SEMIINSULATING GAAS CRYSTALS

For the first time a complete analysis of nearly 800 dislocations in Liquid Encapsulation Czochralski (LEC) GaAs wafers was performed. By calculation of Schmid factors for all glide systems using reported values of thermal stresses it could be shown that dislocations building up the cell walls penetrate the crystal from the outer periphery. Moreover, Arsenic (As) precipitates were observed in all wafers as a second defect type. The distributions of their sizes before and after post-growth annealing were studied yielding valuable information on As diffusion in GaAs.