Doping of ZnSe during molecular beam epitaxial growth using an atomic phosphorus source

Abstract

Zinc selenide films were doped with phosphorus during molecular beam epitaxial (MBE) growth by employing a novel, valved, three-zone solid-source radio frequency (rf)-cracker unit manufactured by Oxford Applied Research (OAR). Optical emission spectroscopy analysis of the plasmas produced in the rf chamber of the unit showed that the apparatus was capable of generating a flux of atomic phosphorus. By suitably adjusting the operating conditions of the unit, phosphorus concentrations in ZnSe epilayers were varied over the range of 1×1016 cm−3 to high-1018 cm−3, in a highly controlled and reproducible fashion. Phosphorus atoms, in contrast to P4 molecules, were found to be highly chemically reactive at the growing ZnSe surface at a normal growth temperature (around 300 °C), and the OAR unit was found to be eminently suitable for the provision of atomic P for MBE growth. Doping using atomic P was found, at least in lightly to moderately doped ZnSe, to provide an acceptor state that gave rise to a neutral-acceptor bound exciton emission located at 2.7919 eV, in keeping with that of other substitutional acceptors in ZnSe. Also, compensation in atomic P doped ZnSe appears to occur by virtue of the formation of shallow donor states rather than via the production of deep level states, which dominate in the case of most of the previously reported phosphorus-doped ZnSe studies.