Cathodoluminescent Studies of Laser Quality GaAs

Using an ion-pumped scanning electron microscope, cathodoluminescent (CL) studies of striations, dislocation-induced defects, and the doping behaviour of Te, Se, and Si in GaAs, have been carried out. The striations in heavily Te-doped Czochralski material were different from those previously reported in that they possessed a very regular spacing which agreed well with the growth/revolution of the ingot. They were studied as a function of temperature, excitation and position on the crystal face. It is thought that these bright striations in highly-doped material correspond to regions of decreased Te concentration in agreement with earlier work. However, infra-red studies of striations at lower concentrations have shown that the bright striations correspond to an increase in Te concentration. These results are consistent with earlier work relating CL efficiency to doping level. Studies of the dislocation-induced defects and their reactions with the striations in Te-doped material are all consistent with the formation of a Cottrell atmosphere at the dislocations at the expense of the immediate surrounding volume. Comparisons between Te-, Se-, and Si- doped material prepared by three different methods have revealed differences, especially in the case of Si where direct observation of its amphoteric nature were recorded.