MBE heterostructure device instabilities related to interfacial carbon impurities

Abstract

MBE AlGaAs/GaAs heterostructures have been grown on semi-insulating GaAs wafers that received a standard pre-deposition wet chemical etch, while other wafers were subjected to ultraviolet-ozone radiation in addition to the standard pre clean. The ultraviolet-ozone radiation serves to reduce the concentration of carbon on the GaAs wafer surface. Enhancement and depletion mode field effect transistors were fabricated on these wafers. Device anomalies associated with the presence of deep levels were found for the standard cleaned wafers. We present device properties such as current-voltage characteristics, sidegating effects, photoresponse characteristics and output impedance measurements for both wafer preparations. Thermal activation energies for the deep acceptor level were determined from temperature and frequency dependent impedance measurements and conductance deep level transient spectroscopy. The occupation of this deep level for the standard cleaned wafers is explained in terms of the interfacial carbon concentration.