Photoelectron yield spectroscopy on negative electron affinity diamond surfaces: a contactless unipolar transport experiment

On the hydrogen-passivated negative electron affinity (100) and (111) surfaces of diamond no energy barrier prevents photoelectrons from exiting into the vacuum. Therefore, the photoelectron yield spectrum reflects volume rather than surface properties of the material, and the technique is in many aspects similar to photoconductivity experiments, albeit with the advantage of being selective to electrons exclusively (and not to holes). We have employed photoelectron yield spectroscopy to investigate deep defect states in natural and CVD diamond and to determine the electron diffusion length in type II b single crystals. For the latter aspect, the competition between electron and exciton transport plays an important role and the analysis of the yield spectra gives surprisingly large electron diffusion lengths of about 200 mu m. (C) 1998 Elsevier Science S.A.