Analysis of semi-insulating carbon-doped GaN layers using deep-level transient spectroscopy

Electrically active defects in carbon-doped GaN layers were studied with a metal/carbon-doped GaN (GaN:C)/Si-doped GaN (GaN:Si) MIS structure. The GaN:C layers were grown with three different carbon doping concentrations (N-C). A semi-vertical metal/semi-insulator/n-type semiconductor (MIS) device was fabricated to perform deep-level transient spectroscopy (DLTS) measurements. Two electron traps E1 and E2 with energy level at E-C - (0.22-0.31) eV and E-C - (0.45-0.49) eV were observed. E1 and E2 are associated with a nitrogen vacancy V-N-related defect in the strain field of extended defects and a nitrogen antisite defect, respectively. By changing the reverse bias voltage of the DLTS measurement, the location and relative defect concentration of the E1 and E2 traps could be verified. A dominant electron trap E3 with an unusual capture cross section was only observed in devices with an N-C = 2 x 10(19 )cm(-3) GaN:C layer. This may charge carriers from a defect band and lead to the charge redistribution in the GaN:C layer when forward biased. A hole trap H1 with energy level at E-V + 0.47 eV was found for the pulse bias in the forward ON-state. H1 is suggested to correspond with the C-N induced 0/+ donor level. By analyzing the schematic band diagrams across the MIS structure, the carrier transport and defect charging mechanisms underlying the DLTS transient measurements are illustrated. The identification of the trap states in the carbon-doped GaN with different N-C gives further understanding on the carbon doping impact on electric characteristics of GaN power devices made on Si substrates.