Field dependence of the capture and re-emission of charge carriers by shallow levels in germanium and silicon

Abstract

The capture and re-emission of charge carriers by shallow traps in lithium-compensated samples of gallium-doped germanium and boron-doped silicon have been studied by a transient charge drift method. The field dependence of the capture coefficient for hot carriers was observed at low temperatures and high electric fields; capture coefficients of the order of 10 −6 to 10 −7 cm 3 sec −1 were found. The re-emission of the trapped carriers was strongly affected by the electric field. This effect is well explained by a lowering of the Coulomb potential barrier about the trapping centres (the Poole-Frenkel effect) which enhances thermal re-emission. At the highest fields and lowest temperatures, the re-emission from the shallow traps in germanium appeared to be dominated by tunnelling.