Using Deep Level Optical Spectroscopy Methods

Deep acceptor doping is a standard process used in beta-phase gallium oxide (β-Ga₂O₃) electronic devices for compensating background electron concentrations to create semi-insulating component layers needed to enable high voltage and RF devices.  Iron (Fe), magnesium (Mg) and nitrogen (N) are known candidate acceptors with Fe being most common.  However, with its primary energy level at E_C – 0.8 eV, associated with the Fe_Ga defect, device biasing can modulate its charge state depending on device design.  This can cause operational instabilities in b-Ga₂O₃ transistors.  Here we are exploring the behavior of N doping as an alternative acceptor.  Deep level optical spectroscopy (DLOS) measurements reveal its dominant energy level at E_C – 2.9 eV, much deeper than Fe.  However, since this position is below midgap, photocapacitance measurements based on excitation of trapped electrons to the conduction band are difficult to interpret due to competing hole emission to the valence band, which is always possible for photocapacitance studies of bandgap states with activation energies larger than E_G/2.  Here we explore this phenomenon in detail and compare with the more standard Fe characterization.  We show evidence for simultaneous electron and hole emission from this N state, and we elucidate its complex effects on the observed DLOS data and their analysis, which can be erroneous if not accounted for correctly. We present and demonstrate a solution to this issue so that accurate  DLOS characterization can be achieved. Through that process we show that N doping is extremely efficient dopant in b-Ga₂O₃.