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Zinc oxide (ZnO), a wide bandgap (3.37 eV) semiconductor with large exciton binding energy (60 meV), is a promising candidate for optoelectronics application. The bottleneck to harness its capability is linked to the default ntype nature imposed on the material by native defects. Thus, controlling its conductivity (p, i or n) with post growth processes is a strenuous task. Phosphorus is a preferred p-type dopant because of its large solubility. In this report, we have studied the effect of variation in phosphorus implantation time to 40, 60 and 70s on the optical and structural properties of ZnO thin films. Plasma immersion ion implantation technique was carried out to dope the thin film deposited by RF sputter technique and samples were further annealed at 900oC in oxygen ambience for 10s. Low temperature photoluminescence (PL) spectra showed improvement in acceptor behaviour with increase in doping time. Sample doped for 70s exhibited maximum number of acceptor based excitonic peaks at around 3.24, 3.31 and 3.35 eV corresponding to donor-acceptor pair (DAP), free acceptor (FA) and acceptor-bound (AoX) excitons, respectively. High resolution x-ray diffraction showed dominant (002) peak from all samples and increase in phosphorus implantation time shifted the peak towards higher 2θ angle. X-ray photoelectron spectroscopy further suggested increment in phosphorus concentration with implantation time as the number of peaks corresponding to P-O bond observed from P 2p spectra was improved. Scanning electron microscopy images revealed better annihilation of implantation defects post annealing.
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