Electrical characterization of sputter-induced deep levels in GaN thin films synthesized by electrodeposition

Abstract

This paper reports on the presence of deep-level defects in polycrystalline GaN thin films induced during the sputter deposition of Au Schottky barrier diodes (SBDs). The n-GaN films, with a thickness of approximately 300 nm were electrodeposited on (111) Si substrates using a low-cost method and a current density of 3 mA.cm-2 for 3 hours. Structural analysis by X-ray diffraction, scanning electron microscopy, and atomic force microscopy confirmed the polycrystalline nature and good quality of the films. Deep-level transient spectroscopy (DLTS) revealed a broad, asymmetric peak around 265 K in the as-deposited SBDs, indicating the presence of multiple defects. Laplace DLTS resolved four distinct defects with energies ranging between 0.40 eV and 0.60 eV. Thermal annealing between 450 - 500 K increased the reverse leakage current with only minor changes in the forward-bias characteristics. However, annealing at 550 K significantly reduced the leakage current by two orders of magnitude and improved the rectification ratio by one order of magnitude. All samples exhibited significant series resistance. Capacitance-voltage measurements revealed a reduction in the free carrier density near the surface, suggesting the sputter process introduced additional deep level defects. Furthermore, the deep-level energy (and therefore the likely defect composition) was found to be sensitive to the annealing temperature.

HIGHLIGHTS • Sputtering-induced deep levels identified by Laplace DLTS. • Evolution of these defects during annealing at 450-550 K. • Correlation of the deep-level spectra with important diode parameters (Rs, Φb, n). • Enhanced diode performance after 550 K annealing.