Grain-boundary-controlled transport in GaN layers

An exponential dependence of the photoconductivity on the surface photovolt age at GaN layers is predicted theoretically and confirmed experimentally. The prediction is based on the assumption that the material is mainly an or dered polycrystal, consisting of columnar grains. Accordingly, transport is expected to be limited by potential barriers at the grain boundaries, aris ing from the charge trapped at grain-boundary defects. The observed exponen tial dependence provides evidence that strongly supports the model by estab lishing a direct link between the bulk conductivity and the surface potenti al barrier. The same model is shown to successfully explain several other d efect-related findings as well.