Effect of Ga doping concentration on the luminescence efficiency of GaN light-emitting diodes with Ga-doped ZnO contacts

Abstract

P–n junction GaN light-emitting diodes (LEDs) were fabricated using Ga-doped ZnO (GZO) films as electrical contacts and characterized by electroluminescence (EL) and current–voltage (I–V) measurements. GaN p–n epilayers with a total thickness of ~6 μm were grown on c-plane (0001) sapphire substrates by metal–organic chemical vapor deposition. Half region of the p-GaN layer was etched until the n-GaN layer was exposed, and 100-nm-thick GZO contacts were deposited on the p- and n-GaN layers by RF sputtering with varying Ga concentration (nG) from 1 to 5 mol%. Based on the results of Hall effect, photoluminescence (PL), and X-ray diffraction (XRD), the GZO films were expected to act as best electrical contacts for the LEDs at nG = 2 mol%. Under forward-bias conditions, the I–V curves showed diode characteristics except nG = 5 mol%, and the leakage current was minimized at nG = 2 mol%. Two dominant EL peaks of ultraviolet and yellow emissions were observed at ~376 and ~560 nm, and attributed to near-band-edge- and defect-related radiative transitions, respectively. At nG = 2 mol%, the UV EL showed markedly large intensities for all injection currents, consistent with the results of Hall effect, PL, I–V, and XRD.