Phase Segregation and Transformations in Arsenic-Implanted ZnO Thin Films

The conversion of ZnO into a p-type semiconductor remains a major challenge for its application in optoelectronic devices, since up to now neither the suitable type of defects nor the possible role of secondary phase formation during doping has been clarified. Here, the implantation of arsenic into epitaxial ZnO thin films on Alpha-Al₂O₃ (0001) and subsequent isothermal annealing in high vacuum are studied by particle induced X-ray emission, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-implanted ZnO:As films are single phase and exhibit a locally disordered ZnO lattice structure. Zn₃As₂ nanocrystals segregate at 700°C. Due to annealing at 800°C, Alpha-As and Alpha-As₂O₃ are formed. The study demonstrates the role of solid state reactions and secondary phase formation for group V element doping of ZnO that is a promising route to convert this material into a p-type semiconductor.