Metal-semiconductor-metal photodetectors

The main goal of the work presented in this dissertation is to achieve a good performance of metal-semiconductor-metal photodetectors (MSM-PD's) for both Si and ZnO materials. This dissertation is mainly divided into two categories. First, Si-based MSM-PD's with conventional linear interdigitated fingers were designed, fabricated, measured, and simulated. Growth, characterization, and application, such as MSM-PD's and solar cells of ZnO thin films were including in the second part of the work.; The dark leakage current and sensitivity of Si-based MSM-PD's were improved by adding a-Si:H and/or SiO2 layers on top of c-Si, choosing metals with higher work function or using cryogenic processing, and choosing geometry design with smaller size of finger width and spacing.; Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) showed a good crystalline quality of the detectors formed with cryogenic processing. The size of metal grains became smaller and more crystals were formed as temperature decreased.; In the second category, ZnO thin films were deposited either by RF magnetron sputtering or laser assisted molecular beam deposition (LAMBD). Some LAMBD samples were post-deposition excimer laser annealed with pulse energy levels of 103 mJ/cm2 or 206 mJ/cm2, and some RF sputtered samples were annealed at 300 °C in air for 30 minutes.; X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) show both RF sputtered and LAMBD ZnO films were close to a 1:1 Zn:O stoichiometry, with energy bandgap of ∼3.3 eV at room temperature. The surface morphology was observed from field emission scanning electron microscopy (FESEM) and appears to be very rough, implying 3-D growth; crystals formed more tightly and uniformly with heat treatment under air ambient.; The performance of both ZnO MSM-PD's and solar cells was evaluated by means of room temperature dark and photo I-V measurements. Both dark current and responsivities were improved after heat treatment for RF sputtered ZnO MSM-PD's. The value of responsivity for heat-treated devices was increased from 41.9 mA/W to 59.3 mA/W, and the dark current of the as-deposited RF ZnO MSM-PD was found to be three orders lower in magnitude compared to the heat-treated film.