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Wide bandgap of 3.37 eV and large exciton binding energy of 60 meV inherited by ZnO has attracted a lot of attention in order to establish it as a potential candidate for the optoelectronic devices. The main challenge encountered for its efficient utilization is default n-type behaviour of ZnO due to the existence of native donor defects. Therefore, achieving p-type behaviour has been a tough job and significant efforts have been made by the research community over the last couple of decades in this direction. Observing the drawbacks shown by the mono-doped samples in achieving p-type ZnO, co-doping has emerged out to be a promising technology with the benefits of increasing dopant solubility and reducing ionization energy. In this report, we have studied the effects of variation in boron implantation dose by varying implantation time to 2 and 4 s on the behaviour of phosphorus implanted (implantation time of 70 s) ZnO thin films, using plasma immersion ion implantation (PIII) technique. Samples were annealed at 800°C for 10 s in oxygen ambient. High resolution X-ray diffraction (HRXRD) showed enhanced phosphorus solubility for 4 s boron co-doped sample. Improved P-O bonding was observed for higher boron co-doped sample from high resolution X-ray photoelectron spectroscopy (HRXPS) measurement. Low temperature photoluminescence (PL) spectra demonstrated donor-acceptor pair (DAP) and free acceptor (FA) peaks at around 3.24 and 3.31 eV, respectively with 4 s boron co-doped sample showing dominant FA peak indicating improved acceptor based optical emission for it.
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