High-field-induced hot-carrier temperature bandgap narrowing and carrier multiplication in bulk semiconductors

摘要

Abstract: The steady state distribution function of charged carriers which takes into account the energy absorbed by the carriers in an electric field is described. Velocity-field characteristics so obtained agree well with the room-temperature experimental data for silicon samples of varying ohmic mobility. In the nondegenerate approximation, the saturation velocity obtained is comparable to the thermal velocity of the carriers (1.03 $MUL 10$+7$/ cm/s for electrons and 1.00 $MUL 10$+7$/ cm/s for holes), a result which is independent of the low-field mobility of the carriers, consistent with the experimental observations. The asymmetrical distribution function favors holes in the direction of the applied electric field and electrons in the opposite direction. Therefore, on a tilted band diagram, electrons tend to sink and holes tend to float, thereby reducing the effective bandgap. This increases the number of intrinsic carriers with the increase of electric field. An effective hot-electron temperature which accounts for this increase in carrier concentration also increases with the increase in electric field. Effective bandgap, effective hot-electron temperature, and carrier multiplication factor as a function of electric field are analyzed for various doping concentrations. The results so obtained extrapolate well in the limit of zero electric field, when well-known ohmic behavior is reproduced. The implications of this carrier multiplication on pinchoff condition, noise behavior, breakdown characteristics, etc. are discussed.