High performance GZO/p-Si heterojunction diodes fabricated by reactive co-sputtering of Zn and GaAs through the control of GZO layer thickness

The effect of thickness of Ga doped ZnO (GZO) layer on the performance of GZO/p-Si heterojunctions fabricated by reactive co-sputtering of Zn-GaAs target is investigated. GZO films were deposited at 375 degrees C with 0.5% GaAs area coverage of Zn target and 5% O-2 in sputtering atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy show that c-axis orientation of crystallites, Ga/Zn ratio and oxygen related defects depend substantially on the thickness of films. The 200-350 nm thick GZO films display low carrier concentration similar to 10(17) cm(-3), which increases to >10(20) cm(-3) for thicker films. The diodes fabricated with >500 nm thick GZO layers display non-rectifying behaviour, while those fabricated with 200-350 nm thick GZO layers display nearly ideal rectification with diode factors of 1.5-2.5, along with, turn-on voltage similar to 1 V, reverse saturation current similar to 10(-5) A, barrier height similar to 0.4 eV and series resistance similar to 200 omega. The drastically improved diode performance is attributed to small Ga/Zn ratio (similar to 0.01) and extremely low dopant activation (similar to 0.3%), owing to diffusion and non-substitutional incorporation of Ga in thin GZO layers, which cause self-adjustment of doping concentration. These factors, together with c-axis orientation and chemisorbed oxygen at grain boundaries, facilitate ideal diode characteristics, not reported earlier for GZO/p-Si heterojunctions.