Preflashover and flashover phenomena of silicon-vacuum system under pulsed excitation

Rectangular n⁺nn⁺-type silicon blocks with different surface treatments, i.e., one surface is chemically etched and the other is unetched, were used to investigate the characteristics of preflashover and flashover of semiconductor under a high voltage pulse in a vacuum. The metallic contacts were employed to keep a fine contact between the sample and the electrode. For unetched samples, the preflashover current obeyed Ohm's law, and for etched samples, it was dominated by the space-charge limited current. After flashover shots, two kinds of silicon samples showed quite distinct tracks. It is considered that all the phenomena are attributed to the different density and distribution of surface states for two kinds of samples. The developing process of surface flashover across a semiconductor could be explained as the current filamentation which is induced by thermal effects. It is suggested that the flashover occurs in the interface layer of silicon butted to electrodes, and in the lateral layer of silicon near the vacuum ambient with a depth of ∼2 μm.