Determination of Deep Centers in Conducting Gallium Arsenide

A technique has been developed for determining the properties of deep centers in conducting, n-type gallium arsenide. A Schottky barrier is produced at the surface by means of a blocking contact of gold or electrolyte. A reverse bias is applied and the ionization of deep centers in the dark causes the barrier capacitance to change with time. After this, electrons may be injected into the barrier by strongly absorbed light and captured by the deep centers that have previously ionized. Again, the kinetics of the process can be determined from measurements of the barrier capacitance as a function of time. The concentration, energy level, and capture cross section of the dominant center have been determined. It is a donor lying 0.74 eV below the conduction band edge and typically present in concentrations around 1016/cm3. From capture-cross-section data it appears to be negatively charged when occupied. This property is sufficient to limit minority-carrier lifetimes to very small values.