Operating temperature of extrinsic Si photoconductive detectors

Abstract

Extrinsic Si photoconductive detectors require a lower operating temperature than do intrinsic photoconductors of the same activation energy. This paper compares D λ∗, as a function of operating temperature, for extrinsic and intrinsic detectors based on established theoretical relations and measured data. The effects of such parameters as impurity concentration, free-carrier lifetime and capture cross section (σ c) are evaluated. The activation energy dominates the alterable physical parameters of D λ∗( T). The larger σ c of extrinsic Si is shown to be directly related to extrinsic photoconductors requiring lower operating temperatures than intrinsic materials. Of the extrinsic Si temperature-limiting parameters, only σ c shows any promise as a controllable parameter. This study shows that extrinsic Si will remain limited by lower operating temperatures unless its σ c is decreased substantially. Materials with small σ c, measured as having longer lifetimes, would operate at higher temperatures.