THERMAL ANNEALING EFFECT ON LOW-TEMPERATURE MOLECULAR-BEAM EPITAXY-GROWN GAAS - ARSENIC PRECIPITATION AND THE CHANGE OF RESISTIVITY

The post-growth annealing effects on the electrical properties of low temperature (LT-) GaAs grown by molecular beam epitaxy have been investigated. It was found that the resistivity of the LT-GaAs layer increased exponentially with annealing temperature T(A), resulting in an activation energy of 2.1 eV This activation energy is related to the activation energy of arsenic precipitation. Based on hopping conduction theory, an As cluster density N(T), has been estimated from the resistivities of the LT-GaAs layers. The change of density of arsenic clusters with T(A), was found to be of the form N(T)=N(T0) exp(-T/T0), in agreement with values obtained by transmission electron microscopy measurements. The breakdown voltage of the LT-GaAs layer remained almost unchanged as T(A) was increased up to 650-degrees-C, but the breakdown characteristic became soft. The formation of As clusters is held responsible for the soft breakdown of the LT-GaAs layer after annealing.