Electrical characterization of n-type Al0.30Ga0.70N Schottky diodes

Abstract

The carrier trapping properties and current transport behavior of Ni/n-Al0.30Ga0.70N Schottky diodes were quantitatively characterized by a combination of deep level optical spectroscopy (DLOS), thermally based deep level transient spectroscopy (DLTS), current-voltage-temperature (I-V-T), and internal photoemission (IPE) measurements. High quality Schottky diode behavior was observed with an IPE-determined barrier height of 1.66 eV and the observed temperature-independent reverse leakage current behavior was found to be consistent with field emission in reverse bias and thermionic-field emission in forward bias as the dominant transport mechanisms. The trap spectroscopy measurements revealed the presence of several bandgap states located at EC–0.9 eV (seen by both DLOS and DLTS), EC–1.5, EC–3.11, and EC–3.93 eV—all via DLOS. The EC–3.10 level, which is present in very high concentration, is found to correlate with the energy position expected for the cation vacancy in AlGaN, based on the vacuum referred binding energy model for the AlxGa1−xN alloy. The relatively shallow trap at EC–3.93/EV+0.15 eV, which is possibly Mg-related, is also present in significant concentration. The total observed trap concentration in this sample is in excess of the net doping extracted from capacitance-voltage, which will likely impact device behavior and is consistent with the observed I-V-T behavior.