Abstract
This paper describes the properties of photoresistive sensors built on a thin silicon substrate. These fully restriction of hazardous substances compliant devices show high photo sensitivity, comparable to the best performing CdS/CdSe photocells, within a wide range of illumination intensities extending down to low illuminance levels of less than 5 lx of a black-body radiation at 2850 K color temperature. A comparative analysis of the photoconductive gain confirmed better efficiency of the devices with a shorter photoconductive channel length. The photoconductive gain was shown to increase with the illuminance level, exceeding unity at certain illuminance levels specific for the photoconductive channel length and applied voltage bias. Such behavior was suggested to occur due to the retardation of the minority carrier collection by the potential barrier formed by a high-low junction within the photoresistor's contact regions, which allows more than one majority carrier collection by the electrode per each collected non-equilibrium minority carrier. The physical mechanisms affecting the photocurrent and resistance dependence on the applied voltage bias and illumination intensity are discussed.
Highlights
Silicon photoresistive sensors have been known for many decades
The photoconductive gain was shown to increase with the illuminance level, exceeding unity at certain illuminance levels specific for the photoconductive channel length and applied voltage bias
Such behavior was suggested to occur due to the retardation of the minority carrier collection by the potential barrier formed by a high-low junction within the photoresistor’s contact regions, which allows more than one majority carrier collection by the electrode per each collected non-equilibrium minority carrier
Summary
Silicon photoresistive sensors have been known for many decades. The functional properties, theory of operation, as well as multiple applications were studied comprehensively for the devices based on the crystalline, polycrystalline, and amorphous silicon (Si). Many other semiconductor materials were introduced as basic components for semiconductor light sensitive resistive cells—e.g., CdS, CdSe, PbS, PbTe, and others.. Many other semiconductor materials were introduced as basic components for semiconductor light sensitive resistive cells—e.g., CdS, CdSe, PbS, PbTe, and others.1,2 Some of these materials presented performance advantages over Si, for example, higher sensitivity to light in a visible spectral range and relatively low noise performance, which allowed extensive applications of those photo cells in many fields of science, technology, and engineering Commercially available CdS/CdSe based cells are very sensitive to illuminance levels below 1 lx (less than 0.3 lW/cm of white light illumination at 2850 K color temperature).. While offering undisputable advantages for ambient light detection, some properties of CdS/CdSe prohibited their use in high reliability applications. The resistive sensors based on CdS/CdSe compounds show poor temperature performance (most of them degrade completely at temperatures above $70 C), and their frequency response is limited because of efficient charge trapping responsible for a high photoconductive gain of those sensors
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