Reduced contact resistance and improved surface morphology of ohmic contacts on gan employing krf laser irradiation

Abstract

We employ excimer laser annealing for ohmic contact formation to n- and p-type GaN layers grown on sapphire substrates. The laser irradiation of the n-GaN layers led to increased nitrogen vacancies at the nitride surface, which promoted tunneling currents with a less resistive n-contact. For p-GaN layer, the laser irradiation increased the effective hole concentration that resulted in a reduced contact resistivity. The lowest specific contact resistance measured using the transmission line method was about 2:4 × 10 -7 and 3:2 × 10-4 ωcm2 for n- and p-contacts, respectively. Laser irradiation also resulted in a comparatively good surface morphology as compared to rapid thermal annealing, which in turn improved the transmittance of contacts for light extraction from active layers. It was found out that both the electrical and optical characteristics of the p-GaN contacts exhibited a good thermal stability and an improved transmittance in the blue-green spectral range. An increased forward current with a reduced ohmic contact resistance in such high thermal stable contacts enable the fabrication of GaN light emitting diodes. © 2011 The Japan Society of Applied Physics.