Stationary high‐field domains as tools to measure field‐dependent carrier densities and mobilities in CdS and work functions of blocking contacts

Abstract

AbstractIt is shown that stationary high‐field domains that occur in the range of negative differential conductivity, can be used to clearly identify field‐quenched states in CdS. These are distinguished as cathode‐ and anode‐adjacent domains and permit an unambiguous determination of electron density and mobility as function of the electric field. The anode‐adjacent domain permits additional insight into the high‐field properties of CdS in a field range that is now stabilized in the pre‐breakdown range. Here one finds direct evidence, by using the spectral distribution of the photoconductivity within the domain, of inverting the CdS to p‐type either by more complete quenching or by hole injection from the anode. Both types of stationary domains are determined by the work function of blocking contacts and thereby permit a closer analysis of the contact/CdS interface by shifting the space charge region away from the cathode to the bulk‐side end of the domain. This allows a more precise determination of the dependence of the work function on the photoconductivity of the adjacent CdS. The field‐of‐direction (phase portrait) analysis of the time‐independent transport and Poisson equations allows a simple classification of the two types of stationary high‐field domains relating to the two singular points in the decreasing branch of the current–voltage characteristic. This permits a transparent discussion of the field distribution of these domains that can be directly observed by the Franz–Keldysh effect. Herewith the transition between cathode‐ to anode‐adjacent domains as a function of the applied voltage can be directly followed.