A Unity Quantum Efficiency Photodiode Using Porous Silicon Film
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A UNITY QUANTUM EFFICIENCY PHOTODIODE USING POROUS SILICON FILM J.P. Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson and H.S. Kwok Center for Electronic and Electro-optic Materials and Department of Electrical and Computer Engineering State University of New York at Buffalo Amherst, NY 14260 ABSTRACT A highly sensitive photodiode was fabricated with a metal-porous silicon junction. The spectral response was measured for the wavelength range from 400 nm to 1.075 jim. It was demonstrated that close to unity quantum efficiency could be obtained in the wavelength range of 630 to 900 nm without any anti-reflective coating. The detector response time is about 2 ns for a 9 volts reverse bias. The acceptance angle of photodiode is 2 times better than that of conventional Si detectors. The uniformity and stability were also studied. Possible mechanisms are discussed. INTRODUCTION Since Canham[l-31 demonstrated visible light photoluminescence from porous silicon (PS), much effort has been focused on the possibility of producing optoelectronic devices using this new material. Koshida et al[41 reported that visible electroluminescence was obtained from PS. There is a strong possibility of integrating silicon based electronic devices with this new class of opto-electronic material. We[5] have reported that a highly efficient photodetector can be made with a PS based device. In this paper, we would like to discuss some important characteristics of this new photodiode. Certain characteristics of this photodiode compares favorably with commercial pintrinsic-n (PIN) diodes. SAMPLE PREPARATION Two different kinds of samples were made. For sample A, we started with an (100) oriented, 190 9l-cm boron-doped, 350 pm-thick silicon wafer. For sample B, we started with an (100) oriented, 3 fl-cm phosphorus-doped, 250 pm-thick silicon wafer. For sample B, a p-n junction was formed by the solid-state diffusion before anoidization. A p+ layer with a thickness 34 jim was formed at 1150 'C for 5 hours with a BBr 3 disk. Before anodization, the wafer was cleaned with trichloroethylene, acetone, methanol and deionized water. The native SiP 2 layer was etched by HF(49%) acid. An ohmic contact was formed by evaporating a thin Al film onto the back of the wafer. During the anodization, this back side was covered with an acid-proof wax for protection. The PS layer was formed by anodization in a 50-50 ethanoVHF(49%) solution at a current density of 50 mA/cm 2 for 1-4 minutes and then air dried. The thickness of the PS layer was about 1-10 pjm. Sample A was anodized under room light and sample B under irradiation from a 350 Q halogen lamp. An Al contact was subsequently deposited onto the PS side. No further
Mat. Res. Soc. Symp. Proc. Vol. 283. @1993 Materials Research Society
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annealing was performed. Finally, the samples were cut into a 3x3 mm cells. The Al contact on the PS layer was in the form of a frame of width 200 pim. These ohmic contacts were applied by thermal evaporation in a 10-6 torr vacuum with 99.99% pure Al. The rest of the PS surfac
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