Electrical properties and deep traps spectra in undoped and Si-doped m-plane GaN films

摘要

Structural and electrical properties of nonpolar m-GaN films grown on m-SiC using standard metalorganic chemical vapor deposition (MOCVD) and two versions of sidewall epitaxial lateral overgrowth were studied. It is shown that lateral overgrowth allows one to dramatically reduce the dislocation density from over 10~9 cm~(-2) to ～10~7 cm~(-2). In good correlation with that we observed a strong reduction in the density of electron traps E_c-0.25 eV and E_c-0.6 eV from over 10~(15) cm~(-3) to ～10~(14) cm~(-3), respectively, in MOCVD m-GaN and in laterally overgrown m-GaN. Preliminary studies of the effects of changing the Ⅴ/Ⅲ ratio and of Si doping were performed. The MOCVD m-GaN films grown with high Ⅴ/Ⅲ ratio of 1000 were semi-insulating, with the Fermi level pinned near the 0.6 eV traps. Decreasing the Ⅴ/Ⅲ value to 250 shifted the Fermi level upward, close to the level of the 0.25 eV traps. Si doping in laterally overgrown samples strongly suppressed the formation of major electron traps but enhanced the formation of hole traps near E_u + 0.9 eV. We also report on electrical properties of the GaN interface with the AlN buffer used to facilitate good quality growth on SiC. These properties are dominated by a high concentration of 0.15 eV traps.