Journal of Applied Physics vol:73 issue:6 pages:3074-3081
The experimental transient behavior of Si metal-oxide-semiconductor transistors (MOSTs) operated at liquid-helium temperatures in the prekink, clockwise hysteresis regime is described in detail. As is shown, the drain current exhibits a pronounced decay, after switching on the device, both in n- and pMOSTs. The effective ''exponential'' time constant tau of the transient is in the order of seconds to hundreds of seconds and is a strong function of the gate, the drain, and the substrate biases. Generally, a strong reduction of tau with increasing drain current is observed. These findings are critically discussed in view of the dominant dopant ionization mechanisms at 4.2 K. It is demonstrated that the reported drain current dependence of the transient time constant can be interpreted by considering shallow-level impact ionization by the channel carriers. It is furthermore demonstrated that the anomalous transients occasionally observed point to the occurrence of the reverse process, namely capture of free carriers. By considering these two mechanisms, a comprehensive model for the prekink hysteresis behavior is established.