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S-H Wu, C-C Lin, M. Zhu, Y. Kuo, "Light Wavelength Effects on the Performance of a-Si:H PIN Photodiode," MRS Proc. Symp. A: Amorphous and Polycrystalline Thin-Film Silicon Science and Technology, San Fransisco, CA, April 9 - April 13, 2012.


The amorphous silicon (a-Si:H) PIN diode poses a number of unique properties such as broad spectral response, large area capability, high radiation resistance, low fabrication cost and easy to integrate with the read-out electronics, which are suitable for many electronic and optoelectronic applications. By quantifying the stored charge in the diode illuminated under light of different wavelengths, the spatial distribution of a spectrum of visible light can be obtained using an array of small size detectors made of a-Si:H PIN diodes. In this study, the charge storage of single amorphous silicon PIN diodes of two difference i-layer thicknesses, i.e., 2 µm and 0.3 µm, under various light illumination conditions, i.e., red (625 nm), green (530 nm), and blue (470 nm), is studied. The light with the long wavelength penetrates deeper into the a-Si:H layer and generates more electron-hole pairs than the light with the short wavelength. For the thick i-layer diode, under the negative gate voltage (Vg) condition, the leakage current slightly increases with the wavelength but the charge storage capacitance increases with the wavelength. Under the positive Vg condition, both the leakage current and the charge storage capacity increase with the wavelength obviously. For the thin i-layer diode, the characteristics are very different. Under the negative Vg condition, the leakage current under the light illumination condition is higher than that in the dark. However, it is independent of the wavelength. The charge storage capacitance slightly increases with the wavelength. Under the positive Vg condition, the leakage current increases slightly under the red light exposure. However, the charge storage capacitance under the light exposure condition is the same as that in the dark. In summary, the leakage current and charge storage capacity of the diode are determined by the efficiency of the generation of electron-hole pairs, the depletion of the charges, and the injection of charges from the electrode.

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