Development, Synthesis and Characterization of II-IV-V Chalcopyrite Thin Film for Photovoltaic Device Application
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During last few years much research attention has been devoted for the development and design of new highly efficient economic optoelectronic devices to replace Silicon (Si) based devices for commercial application in various field. The major disadvantage for Si based devices is the indirect electronic bandgap which limits the devices efficiency. This work exhibits the growth, characterization and device application of a novel lead (Pb) free material ZnSnP2 as a replacement of Si. Here, we have successfully grown the ZnSnP2 thin film on p-type silicon (001), sapphire and glass substrate by physical vapor deposition technique for the very first time. It is also evident that during growth the deposition rate plays a significant role to determine the bandgap. At higher growth rate the bandgap of ZnSnP2 thin film decreases due to increasing cationic disorder. Temperature and power dependent photoluminescence properties indicate that the peaks have originated due to donor-acceptor pair related transition. For photodetector application Mg/ZnSnP2/Sn structure is fabricated to operate in the UV-VIS-NIR region of the electromagnetic spectrum. The observed current-voltage characteristics show roll-over like features which was successfully modeled considering two Schottky diodes connected back to back. The maximum values of responsivity, photosensitivity and detectivity are found to be of 29.58 mAW-1, 1.0x102 cmW-1 and 9.42x1010 cmHz1/2W-1 in the forward bias and 0.0076 AW-1, 1.2x102 cm2W- and 15.53x1010 cmHz1/2W-1 in the reverse bias, respectively at illumination of wavelength 850 nm and it offers very fast response speed of 47 μs. The performance of the photodetector is investigated from energy band diagram and to improve it the Sn contact was annealed at 250o C for one hour to reduce barrier height and the respective junctions were treated individually. After annealing the obtained values of the responsivity and detectivity are found to be of 0.2 AW-1 and 4.62x1012 Jones for the Mg/ZnSnP2 and 0.03 AW-1 and 1.62x1011 Jones for the Sn/ZnSnP2 junctions, respectively when they were operated without bias. Under a bias of 2.5 V, these values enhance to 4.7 AW-1 and 1.19x1012 Jones in case of Mg/ZnSnP2 and 12.7 AW-1 and 4.78x1011 Jones for Sn/ZnSnP2 junctions, respectively. The variation of photocurrent is super-linear with the illumination power with the values of the power exponent for the Mg/ZnSnP2 and Sn/ZnSnP2 junctions of 1.75±0.19 and 1.42±0.21, respectively.
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Physical Sciences, Physics, Physics Condensed Matter