Comparative study of deep levels in GaN grown on different templates

Abstract

Deep levels in thin GaN epilayers grown by metal-organic chemical vapor deposition on different templates were studied by photocapacitance spectroscopy and deep-level transient spectroscopy (DLTS) using Schottky barrier diodes. We observed the reduction of electrically and optically active traps in GaN grown with in situ SiN x nanonetwork and SiO 2 striped mask or conventional epitaxial lateral overgrowth technique (ELO) as compared to a typical control layer on a sapphire substrate. All samples measured by DLTS in the temperature range from 80 K to 400 K exhibited traps with activation energies 0.55-0.58 eV and 0.21-0.28 eV. The lowest concentration of both traps was achieved for the sample with 6 min deposition of SiN x nanonetwork, which was lower than that for the sample prepared by conventional ELO, and much lower than that in the control. The steady-state photocapacitance spectra of all samples taken at 80 K over the spectral range 0.75-3.50 eV demonstrated a similar trend for all the layers. The photocapacitance spectra exhibited defect levels with optical threshold energies of 1.2-1.3, 1.6, 2.2 and 3.1 eV. The determined concentrations of traps were compared and the results were consistent with DLTS measurements. The layer with SiN x nanonetwork has the lowest concentrations of optically active traps with the standard GaN control layer being the worst in terms of trap concentrations. The consistent trend among the photocapacitance spectroscopy and DLTS results suggests that SiN x network can effectively reduce deep levels in GaN, which otherwise can deteriorate both optical and electrical performance of GaN-based devices.