Ultrahigh-sensitivity CdS photoconductors with instant response and ultralow power consumption for detection in low-light environments

Abstract

In this study we describe a low-cost cadmium sulfide (CdS) photoconductor that behaves as a highly sensitive and rapidly responding detector toward low-intensity light. Through the observation of TEM images and analysis of micro-Raman spectra, the degree of crystallization of CdS films increased and their dislocation defects were removed effectively after treatment with several shots from a KrF excimer laser. Such laser treatment of CdS photoconductors could be conducted in air and completed within a few seconds. At a very low bias voltage of 1 mV, the laser-treated CdS device provided a record high responsivity of 7200 A W⁻¹ and a detectivity of 10¹⁵ Jones. In addition, at a normal bias voltage of 1 V, it displayed an extremely high responsivity of 7 × 10⁶ A W⁻¹ and a detectivity of 6 × 10¹⁶ Jones. The measured response time of the laser-annealed CdS device from the dark to illumination at 10⁻² fW μm⁻² was only 40 ms—much faster than the shutter speed or exposure time required for a professional digital camera for such low-light image detection. Accordingly, KrF laser annealing is a simple and rapid process that can significantly enhance the low-light detection properties of CdS, a commercial photoconductor. Our strategy proposed herein appears to hold great potential for ultralow-light image detection with ultralow power consumption.