Deep states in nitrogen-doped p-ZnSe

A comparative study on deep levels in p-ZnSe grown by molecular beam epitaxy (MBE), metalorganic MBE (MOMBE), and metalorganic vapor phase epitaxy (MOVPE) has been carried out to elucidate the nature of deep levels. A hole trap level which is located at 0.38 eV above the valence band is inevitably introduced into p-ZnSe by nitrogen doping. The formation of other hole traps, which are associated with native defects due to nonstoichiometry of ZnSe, depends on growth methods and conditions. Electron traps were also observed in MOMBE and MOVPE-grown samples. The absence of the electron trap levels in MBE samples indicates that the traps originate from insufficient decomposition of metalorganic source precursors. These findings illustrate the necessity of forming p-ZnSe (1) under stoichiometric conditions, (2) with novel growth/process techniques to suppress evaporation of Zn and Se, and, (3) with well-decomposed metalorganic sources, in order to achieve p-type doping with a low degree of compensation by hole and electron traps.