| Summary: | 碩士 === 國立中央大學 === 電機工程研究所 === 87 === Abstract
In this study, the metal-semiconductor-metal photodetectors (MSM-PD's) with a hydrogenated amorphous silicon (a-Si:H) film deposited on 〔100〕 silicon wafer have been studied. Two kinds of MSM-PD device, one had the recessed Cr electrodes and the other had the recessed ITO (Indium-Tin-Oxide) transparent electrodes have been fabricated on Si wafers and their characteristics were compared. The MSM-PD with recessed ITO electrode had a higher responsivity than that of the one with recessed Cr electrode. This could be due to that the MSM-PD with the transparent ITO electrodes had a larger light absorption region than that of the one with Cr electrodes. The Si MSM-PD with an i-a-Si:H heterojunction, 1.0 μm-deep recessed Cr electrodes, and 5 μm finger width and spacing, had a responsivity of 0.263 A/W measured at 0.83 μm incident-light wavelength and its quantum efficiency was estimated to be 39%. The corresponding MSM-PD with recessed ITO electrodes had a responsivity of 0.53 A/W and its quantum efficiency was estimated to be 79%. These experimental results indicated that the ITO electrodes could be used to obtain a responsivity two times higher. But, the resistivity of the used ITO film was higher than that of a Cr film. This caused a RC delay time and hence its 3 dB bandwidth to less than that of the one with Cr electrodes. So, the resistivities and transmittances of ITO films sputter-deposited under various process conditions were studied also. The higher the substrate temperature during deposition, the higher the film quality, in terms of electrical conductivity. By suitably adjusting the O2 flow-rate during sputtering deposition of ITO film with Ar/O2 plasma, the resistivity of the obtained ITO film could also be reduced. It was also found that the obtained ITO films were highly transparent for visible light, and exhibited a high reflectance for infrared light.
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