Spectral signature of near-surface damage in CdTe X-ray detectors

Abstract

Knowledge of the response matrix of an X-ray detector is an important prerequisite for efficient use. This matrix is usually complicated due to the multitude of effects that determine the photon interaction and energy detection processes. Consequently, assembly of a response matrix often proceeds via simulation, modelling features of the detector and using experimental data as input.

This paper is concerned with one such feature: the spectral signature of a near-surface damage layer in cadmium telluride semiconductor detectors. An empirical modification to the well-known Hecht relation is proposed that allows an improved description of the spectral shape, and an interpretation in terms of a depth-dependent carrier drift length (lifetime) near the surface is developed. Applying this to both the front and the rear surface, good agreement between measurement and simulation is obtained for the 31 keV and the 81 keV photon lines of barium-133. The near-surface modification reaches to a depth of 100-200 μm.