Site disorder and its tailoring in N implanted post-annealed ZnO: Prospects and problems. (15th November 2021) - Mondal, Apu
Abstract: The particular role of nitrogen in ZnO as a p type dopant remains a debated topic of research till date. In this work, Raman and Photoluminescence (PL) investigations have been carried out on N implanted granular ZnO with subsequent rapid thermal and conventional furnace annealing (at 750 °C) in oxygen and air ambient. Raman results indicate that rapid thermal annealing is efficient to recover irradiation generated disorder keeping doped N at the lattice site. Conventional furnace annealing, on the other hand, promotes outdiffusion of atomic N from lattice position along with vacancy agglomeration to some extent. No matter whether annealed or not, implanted N prefers to accumulate near the stacking fault defects and increases the well known free to bound transition (here ~ 3.314 eV at 10 K) in ZnO. Still, low temperature PL spectra of the samples show convincing evidences of acceptor bound exciton transition energetically just below the same due to dominant donor bound excitons. Shallow donor to shallow acceptor PL emission has also been clearly identified. The possibilities and problems of hole doping in ZnO via N ion implantation have been discussed in the light of previous reports. At the end, some futuristic proposals have been formulated. Highlights: Granular ZnO samples have been implanted by N ions with subsequent post-annealing. Rapid thermal annealing lowers strain but annealing for longer time scale promotes vacancy clustering. Incorporated nitrogen prefers to accumulate near stacking fault defects. Low temperature photoluminescence shows evidence of shallow acceptor bound excitons.