Surface doping: a special feature of diamond

A unique feature of diamond surfaces is a highly conductive p-type layer, w hich is usually observed when the surfaces are hydrogen terminated. This ph enomenon has recently attracted a lot of interest since a number of electro nic applications proposed for diamond are based on the effect. Nevertheless , its microscopic origin is still a matter of debate. In this paper we prop ose an electron transfer from the diamond valence band to adsorbates at the surface to be the effective doping mechanism. These adsorbates act not as isolated species but as components of a mildly acidic aqueous surface layer and thus charge exchange has to be described by electrochemical arguments. The model is supported by experiments, which show that the hydrogenation o f the surface is necessary but not sufficient for inducing the hole accumul ation layer at the surface.