Noise and response characterization of a HgCdTe photoconductive detection system

Thesis (M.S.)--University of Rochester. College of Engineering and Applied Science. Institute of Optics, 1981. This thesis was digitized by the Institute of Optics in 2014 and was determined to have lapsed into the public domain. If you are the author and have questions about the digitization of your work, please contact Kari Brick, Graduate Program Coordinator for the Institute of Optics, at kbrick@ur.rochester.edu. Other contact information for the Institute is available at http://www.optics.rochester.eduIt was found that the responsivity and detector noise of a Hg₀.₈Cd₀.₂Te photoconductive detection system show deviations from linearity at large flux levels. Laboratory measurements of detector characteristics are interpreted using physical models developed to describe the photoconductive process. Response measurements show that at low flux levels the detector conductance increases linearly with the incident photon rate, but at high photon fluxes, the response falls off to become proportional to the square root of the photon rate. This effect is due to a carrier lifetime that changes with the incident flux. In the small signal limit, the carrier lifetime is nearly constant, but at high photon fluxes, it rapidly decreases because of donor impurities which affect the recombination processes present in the detector. Interpretation of the noise measurements shows that the generation-recombination process constitutes the predominant noise source in this detection-system. The system is found to be background limited, and the conductance fluctuations increase linearly with the photon rate at low flux levels, and then saturate in the limit of high flux levels. This behavior is in agreement with the change of conductance with photon flux level. Noise measurements made with large detector bias currents show that the model predicts more noise than is actually present in this limit. This suggests that the standard, simple model of generation-recombination noise presented in this thesis is not adequate to treat the noise characteristics under high-background conditions