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 inves tigated. It was found that the resistivity of the LT-GaAs layer increa sed exponentially with annealing temperature T(A), resulting in an act ivation energy of 2.1 eV This activation energy is related to the acti vation energy of arsenic precipitation. Based on hopping conduction th eory, an As cluster density N(T), has been estimated from the resistiv ities 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 agre ement with values obtained by transmission electron microscopy measure ments. The breakdown voltage of the LT-GaAs layer remained almost unch anged as T(A) was increased up to 650-degrees-C, but the breakdown cha racteristic became soft. The formation of As clusters is held responsi ble for the soft breakdown of the LT-GaAs layer after annealing.