Low interface trapped charge density in MBE in situ grown Si3N4 cubic GaN MIS structures

Abstract

In this work we report on the electrical characterization of nonpolar cubic GaN metal–insulator–semiconductor (MIS) structures. Si3N4 layers were deposited in situ on top of cubic GaN grown on 3C–SiC (0 0 1) substrates. The electric characteristics of the MIS structures are determined by current–voltage measurements and by capacitance and admittance spectroscopy techniques. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to investigate the composition of our samples. From the flat band voltage in the MIS capacitors and a detailed band diagram analysis, the conduction band discontinuity of Si3N4 and cubic GaN was evaluated 1.17 eV, which is slightly lower than reported for hexagonal GaN. By admittance spectroscopy interface state densities are calculated. Current–voltage characteristics were used to evaluate the influence of the substrate temperature on the insulating properties of the MIS structures. The energetic position of the interface traps was found to be about 0.3 eV below the conduction band of cubic GaN. The density of these traps is 2.5 × 1011 cm−2 eV−1. We find a conductivity minimum in the MIS structure grown at 600 °C.