  Phosphorene, the monolayer form of the (black) phosphorus, was recently
exfoliated from its bulk counterpart. Phosphorene oxide, by analogy to graphene
oxide, is expected to have novel chemical and electronic properties, and may
provide an alternative route to synthesis of phosphorene. In this letter, we
investigate physical and chemical properties of the phosphorene oxide including
its formation by the oxygen adsorption on the bare phosphorene. Analysis of the
phonon dispersion curves finds stoichiometric and non-stoichiometric oxide
configurations to be stable at ambient conditions, thus suggesting that the
oxygen absorption may not degrade the phosphorene. The nature of the band gap
of the oxides depends on the degree of the functionalization of phosphorene;
indirect gap is predicted for the non-stoichiometric configurations whereas a
direct gap is predicted for the stoichiometric oxide. Application of the
mechanical strain and external electric field leads to tunability of the band
gap of the phosphorene oxide. In contrast to the case of the bare phosphorene,
dependence of the diode-like asymmetric current-voltage response on the degree
of stoichiometry is predicted for the phosphorene oxide.
