Fabrication and characterization of solution processed colloidal ZnO quantum dots based spectrum selective ultraviolet photodetectors

Abstract

The key motivation of this thesis is to investigate the fabrication and characterization of some ZnO colloidal quantum dots (CQDs) based spectrum selective ultraviolet (UV) photodetectors (PDs). Devices have been fabricated either in the form of interdigitated metal-semiconductor-metal (MSM) structure using glass substrates or in the Schottky diode structure on the silicon substrates by using solution processed ZnO CQDs as the active layer the UV detectors. The spin-coated ZnO CQDs have been annealed at 450 oC for the spectrum selective applications. The spectrum selectivity has been achieved by the quantum confinement of carriers in the ZnO CQDs without using any external filter which is commonly used for silicon based spectrum selective photodetectors. The ZnO CQDs have been used in the present study due to their larger surface-to-volume ratio and better performance in terms of the responsivity, spectrum selectivity and response speed another ZnO nanostructure based UV photodetectors. The particle-size dependent electronic and optoelectronic properties of the ZnO CQDs may enable us to tune the peak detectivity wavelength of the detector by fixing the QDs size to the desired value at the time of the synthesis process. Thus the solution processed ZnO CQDs also provide the platform for low-cost low-temperature fabrication of large-area UV photodetectors with a narrowband photoresponse characteristics. An attempt has also been made to improve the photoresponse of the ZnO CQDs based MSM UV photodetector by introducing a scattering layer in the device. In this case, a layer of solution processed ZnO nanoparticles (NPs) has been deposited on the interdigitated MSM UV structure fabricated on a glass substrate and UV illumination has been provided from the back side of the device to improve its responsivity while maintaining fixed spectrum selectivity.