Mechanism of reverse current increase of vertical-type diamond Schottky diodes

Abstract

Current transport at p-diamond Schottky contacts under reverse bias operation was investigated. Reverse current transport modes of several types were observed depending on the bias voltage range: thermionic emission (TE) associated with the image force barrier lowering was dominant in the lower voltage range of <50 V, whereas thermionic-field emission (TFE) mechanism governed transport in the higher voltage range. The Schottky barrier height ϕb estimated from the reverse characteristics was lower than that obtained from the forward characteristic by more than 0.4 eV, which indicates that the low Schottky barrier height ϕblow area localized in the patch shape at the diamond Schottky contact. This Schottky contact inhomogeneity was found to increase the reverse current effectively even though the ϕblow area is smaller because the reverse current in TE mode flows preferentially through ϕblow patches. The current transport mode changed from TE to TFE when the maximum electric field was >1 MV cm−1, which indicates that a strong electric field concentration exists at the Schottky electrode fringe. When the high reverse voltage was biased, a sudden current increase occurred, followed by a permanent increase of reverse current, indicating that mid-gap defects were formed at the interface. These results indicate that reverse current and electric-field breakdown have different origins.