Control of stoichiometry dependent defects in low temperature GaAs

MBE grown GaAs deposited at low temperatures (LT-GaAs) has already found industrial use as passive buffer layer or gate isolation layer in FETs and as active layer in THz photodetectors. Although LT-GaAs was extensively studied in the past, the role of stoichiometry dependent defects governing the unique properties is not yet fully understood. This study describes the systematic variation of the growth parameters, i.e. growth temperature and As/Ga flux ratio, to control the point defect concentrations. The lattice mismatch between the LT-GaAs layers and the GaAs substrates, which is caused by the incorporation of excess As, decreases with increasing growth temperature and with decreasing As/Ga flux ratio. A linear correlation of the arsenic antisite concentration As_Ga with the lattice constant is observed. A well defined As_Ga concentration can be established either by varying the growth temperature or by choosing a certain As/Ga flux ratio. After annealing at 600 °C all samples exhibit a high electrical resistivity. A single activated behavior with activation energies typical for band conductivity is observed in temperature dependent measurements of the conductivity of n-i-n structures. However, the energy barrier decreases with higher growth temperatures.