Photoluminescence (PL) and ohmic contact resistance measurements were used to characterize the n-GaN surface treated with reactive ion etching (RIE). The n-GaN him was grown on a sapphire substrate by a metal organic chemical vapor deposition process. Subsequently, the GaN film was etched with BCl3 or Ar gas prior to the PL measurement and contact metal Ti/Al deposition. In PL spectra, we observed the peak shift of the impurity-related emission (yellow luminescence (YL)) for both BCl3 and Ar etched n-GaN films. The amount of this wavelength shift increases with the RIE rf power increase and depends on the species of the etching gases. The shift of the YL peak decreased after thermal annealing at 500 degrees C for 30 s. The YL peak shift may be attributed to the RIE induced surface point defects. In the ohmic contact resistance measurements, the transmission line model technique was used. The contact resistance of the RIE etched surface is around 5.4 x 10(-4) Omega cm(2). However, a lower contact resistance of 5.7 x 10(-6) Omega cm(2) was obtained for a native surface of n-GaN film. No obvious distinction between the roughness of etched and native GaN surfaces was observed by the atomic force microscope measurements. In an Xray grazing diffraction measurement, the crystalline lattice orientation and the coherent length of native n-GaN layer were better than the etched n-GaN according to the results of the rocking curve and Theta-2 Theta scan. (C) 1999 Elsevier Science Ltd. All rights reserved.
