Title: Impact of positive space charge depletion layer on negatively charged and neutral centers in gold–diamond Schottky junctions

Abstract: It has been widely accepted that conversion between negatively charged nitrogen-vacancy (NV⁻) center and neutral nitrogen-vacancy (NV⁰) center can be realized with the Fermi level crossing the transition level corresponding to the ground state of NV⁻. In this study, a suppressing effect was observed in the emission of NV⁻ center; however, emission of NV⁰ center was not observed to be increasing as expected and was stable when lowering of the Fermi level was induced by a Schottky junction between gold and oxygen-terminated diamond containing NV centers. The relationship between the thickness of the depletion layer as well as that of the suppression layer, appearing when the Fermi level shifted below the ground state level of NV⁻, and the donor concentration was derived. Moreover, a model based on the assumption that an intermediate transition level (nonfluorescence state) existed between the ground state energy levels of NV⁻ and NV⁰, was proposed to explain why suppressed NV⁻ did not convert to NV⁰. The results of this study will aid in further understanding of the characteristics of NV centers. In addition, a Schottky junction can be developed to determine the charge state of unknown color centers and facilitate study of defects in diamonds.