Papers by Keyword: Photoconductor

Abstract: Photoconductive amorphous selenium (a-Se) layers are utilized in flat panel X-ray imaging detectors as a direct conversion medium, converting X-ray photons directly into electric charge. Commercial a-Se direct conversion Active Matrix Flat Panel Imagers (AMFPIs) have demonstrated superior image quality in mammography, showcasing the potential of this X-ray imaging technology [1-2]. The use of a-Se is limited, however, by its low Z, resulting in low stopping of high energy X-rays [2]. This limitation is not shared by PbO thin films. Earlier PbO films consisted of small poly-crystalline platelets with low film density and suffered from the presence of both oxygen vacancies and impurity phases (PbO₂). Recent advances [3-4] have yielded dense amorphous PbO (a-PbO) films with apparently uniform stoichiometry, as confirmed by X-ray photoelectron spectroscopy (XPS). More careful analysis [5] using X-ray absorption spectroscopy (XAS) indicated some tailing of the conduction band, which was attributed to suspected O-vacancies. An annealing study on a-PbO [3] indicated a transition to β-PbO around 500 C. X-ray diffraction (XRD) data of the β-PbO (annealed a-PbO) film matched that of a β-PbO reference, while XAS data did not. This was attributed to the different depths of the sample volumes probed by the two techniques. Doppler-broadened positron annihilation spectroscopy (DBPAS) was conducted on several a-PbO samples synthesized under different conditions using the McMaster Variable-Energy Positron Beam (MVEPB) and the results were modelled using VEPFIT [6]. All samples were found to have a three-layer structure, with the bulk S-parameters between 0.4725 and 0.4753. The two other layers were contained within the first 300nm of the film and varied in thickness, diffusion length and S-parameter value. This confirms the suitability of DBPAS, as a sensitive probe of vacancy-type defects and the layer structure of thin films, to guide the optimization of a-PbO synthesis for photoconductive detectors. Work is underway to produce a series of samples which vary systematically in their synthesis conditions to establish synthesis-structure relationships.

Abstract: Zinc oxide (ZnO) has attracted considerable attention because of its potential applications in optoelectronic devices. Many scientists have reported on the preparation of ZnO based photodetectors in metal-semiconductor-metal (MSM) structures where expensive noble metals are used as electrodes. Here, we propose the preparation of full metal-oxide photoconductors by using indium tin oxide (ITO) as the electrodes and ZnO thin films as sensing materials. ZnO thin films were prepared by employing a simple ultrasonic spray pyrolysis (USP) technique with a commercial ultrasonic nebulizer (1.7 MHz). In this work, we developed a high performance ZnO based photodetector on interdigitated ITO with a simple and low-cost USP method. The I-V characteristic shows that ZnO thin film works in a photoconductive mode and has better performance as a UV (325 nm) detector than other wavelengths (505, 625 and 810 nm). As a UV detector, the devices exhibit high sensitivity (1255.51%), high responsivity (22.6 x 10³ A/W), high detectivity (1.49 x 10¹⁴ Jones), good stability, a fast response time of 0.87 s and a relatively slow recovery time of 34.8 s. This high performance may be related to the large crystallite size that facilitates higher electron mobility.

Abstract: The Phenomenon of Laser-Induced Discharging in an Organic Photoconductor Sample Was Directly Observed Using Electron Holography and Sophisticated Techniques for In Situ Observations. Mechanical Friction Was Used to Induce Negative Tribocharges on the Surface of the Photoconductor Sample. the Observation of Equipotential Contour Lines (i.e., the Electric Potential Distribution) outside the Specimen Revealed that the Amount of Tribocharges Was Reduced by the Laser Exposure. Computer Simulations of the Equipotential Lines Provided Useful Information for Evaluating the Quantity of Tribocharges.