The effect of contact barriers on space-charge-limited current injection in impurity-band-conduction photodetectors

Abstract

A theoretical investigation was made on the effect of contact barriers on space-charge-limited (SCL) current injection in impurity-band-conduction (IBC) photodetectors. Parmenter and Ruppel [J. Appl. Phys. 30, 1548 (1959)] considered the effect of contact barriers on SCL current injection in insulators. They solved the steady-state, one-dimensional transport equations, obtaining the solution in terms of integrals, which they evaluated for certain limiting cases. We have modified their approach by using the current injection ratios at the contacts as boundary conditions. This is a very general formulation that can be used for any type of contact barrier. We then applied this technique to model contact barriers in IBC devices. The fact that the IBC hopping mobility is several orders of magnitude smaller than the electron mobility enables us to evaluate the integrals and obtain a closed form solution to the transport equations. Calculated results include current versus voltage behavior, electrostatic potential and electric field versus position for a given bias. It is concluded that the injected electron current is dominant for the store-mode applied bias.