Effects of 532 nm laser-assisted annealing on metal contact to p-GaN

Abstract

In this study, the contact characteristics of p-GaN treated by laser-assisted annealing with different laser fluences were investigated. Based on the two-photon absorption model, a laser treatment on the p-GaN was achieved by utilizing laser with a wavelength of 532 nm. The results showed that specific contact resistance decreased as the laser fluence increased in the low fluence region (<200 mJ/cm2), but deteriorated when the fluence reached to 300 mJ/cm2 or even higher, indicating that laser annealing by 532 nm could greatly affect specific contact resistance. The results of SIMS, photoluminescence spectra, and XPS measurements showed that the enhanced ohmic contact for samples with a low laser injection fluence was attributed to the enhanced aggregation of Mg atoms near the surface and the enhanced activation efficiency of MgGa acceptors by the removal of H atoms from Mg–H complexes. For the samples treated with fluence higher than 300 mJ/cm2, the contact characteristics were compromised due to both the accumulation of gallium oxide on the surface which increased the barrier height of metal/GaN and the formation of structural defects. An improved ohmic contact with a specific contact resistance of 2.93 × 10−4 Ω cm2 were demonstrated for p-GaN with the 200 mJ/cm2 laser fluence. 532 nm laser-assisted annealing treatment has great potential for the selective activation of p-GaN and enhancement of GaN/metal contact characteristics.