Deep Trap Concentrations from Three-Dimensional Carrier Concentration Profiles in Hydride Vapor Pressure Epitaxially-Grown GaN

We have investigated deep trap concentrations in hydride vapor pressure epitaxy (HVPE) - grown GaN by measuring three-dimensional carrier concentration profiles and ionization energies. Schottky contacts were fabricated on 28-68μm thick films using Ni/Au contacts. Extensive capacitance-voltage measurements were made in the temperature range 100-350K at reverse bias voltages in the range 0 to –5V. Effective carrier concentrations and ionization energies were determined from three-dimensional plots of concentration-temperature-depth. Carrier concentration versus temperature plots show slowly changing three-step behavior. During the first step, all the plots rise linearly up to about 200K reaching respective plateaus before reversing courses downwards again linearly. Ionization energy plots, on the other hand, are almost linear all the way up to 350 K showing some tendency of upward bending. Trap concentrations were determined from carrier concentrations and previously measured deep level transient spectroscopy (DLTS) plots as function of reverse bias voltages. In almost every case, trap concentrations also rise linearly with increasing depth in the samples.