Abstract
Photodetectors are among the most widely used optoelectronic devices in numerous commercial and scientific applications. Today, commercially available photodetectors are typically made from gallium phosphide (GaP), silicon (Si) and indium gallium arsenide (InGaAs) for detection in ultraviolet (UV), visible and near-infrared (IR) regimes of the electromagnetic spectrum, respectively. For mid and far infrared lead sulphide (PbS), lead selenide (PbSe), indium antimonide (InSb), and mercury cadmium telluride (HgCdTe) based photodetectors are used. It is therefore highly desirable to have a single, low cost, multi-spectral range photodetector that covers the optical window created by present technologies and does not require cryogenic temperature for efficient operation. In addition, the current photoconductor technologies have high dark currents, poor detectivity, slow response speed, and are not compatible with flexible platforms. The research work in this thesis is aimed to address the major issues related to current photodetector technologies and to develop low cost multispectral photodetector technology. For this, a study on PbS semiconductor nanocrystals and C60 single crystal fullerites is undertaken to develop hybrid photodetector technology. Both these materials have very attractive properties well suited for photodetector device applications such as broadband size-tunable absorption of PbS nanocrystals and high electron mobility of C60 fullerites. A variety of large area (25 mm2) photoconductor devices are demonstrated employing these materials. Photoconductor devices fabricated display a broadband UV-vis-NIR spectral tunability, exhibit a detectivity ~1010 Jones, a responsivity ~0.35 A/W, a linear dynamic range of 80 dB, a rise time 60 μs and signal detection capability up to ~250 kHz. These figures of merit achieved for the photoconductor devices are competitive with the current state of the art technologies. With the additional processing benefits including simple room temperature device fabrication and providing compatibility with large-area flexible platforms, these devices represent significant advances and make PbS nanocrystals and C60 fullerites promising candidates for advanced photodetector technologies. The thesis also includes preliminary studies on photoconductor devices based on single ZnO nanorods.