Electrical properties of nearly stoichiometric GaAs grown by molecular beam epitaxy at low temperature

Nearly stoichiometeric GaAs epilayers doped with Si or Be were grown by molecular beam epitaxy at a low temperature with closely controlled fluxes near the stoichiometric conditions. Excess As point defects in the epilayers which acted as trap sites of free carriers were studied by means of the Hall effect measurements. Under the same As/Ga flux condition, concentrations of excess As point defects which trap free carriers increase with increase of concentrations of Si or Be. With the same concentration of the dopants, on the other hand, concentrations of excess As point defects increase linearly with the As/Ga flux ratio. The dependence of carrier mobility on the trapped carrier concentrations indicates that free carriers are trapped by neutral point defects and change them into ionized ones. In the epilayers which are very close to the stoichiometric composition, Si exhibits its amphoteric nature, occupying both donor and acceptor sites and results in the self-compensation