The field-assisted emission effect on the acceptor energy of GaN:Mg in admittance spectroscopy measurements

A simulation program for admittance calculations in a semiconductor Schottky junction with a trap was developed using physical parameters including the Poole–Frenkel electric field-assisted emission effect. The simulation revealed limitations in the validity of the admittance measurement technique in determining thermal activation energies of semiconductors. The controversy in the observed thermal activation energy of the GaN:Mg structures between the Hall effect and admittance spectroscopy measurements is explained using the simulation results. The admittance measurement technique can only determine the real energies when the overall doping concentration of the shallow (NS) and deep (NT) levels is low and while NT⩽NS. While the condition of NT⩾NS causes a reduction in the apparent measured energies, the electric field built up at the crossover by NS or/and NT further reduces the energies by lowering the barrier potential for the trap emission. Particularly if NT≫NS, the electric field induced by the deep level itself induces the reduction in the barrier potential. This is the case for the rather highly doped GaN:Mg structures.