Far infrared photovoltage effect in a blocked impurity band detector

Abstract

A photovoltage was found across a silicon blocked impurity band detector when illuminated at low temperatures with photons of wavelengths up to about 30 μm. It appears as an open loop photovoltage, constant over a wide range of incident flux intensity, while the short circuit photocurrent changes linearly with photon flux. The device is a boron doped epitaxial structure, sandwiched between degenerately doped thin semitransparent contacts, consists of a pure layer next to a photoactive layer doped in the regime where impurity banding occurs. The short-circuit photocurrent is shown to originate from a ballistic transport across the micrometer thick pure layer of holes photoexcited at the degenerately doped contact with the pure layer. On the other hand, the open loop photovoltage drives across the pure layer a counter ballistic flow of holes thermally emitted over a barrier existing at the interface with the pure layer. The open loop photovoltage at 0 K limit is then a direct measure of the Fermi energy inside the impurity band of the doped photoactive layer.