Integrating Bipolar Junction Transistors with Silicon-Based Light-Emitting Devices
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bandgap semiconductor, is an inefficient light-emitting material. In contrast, porous silicon (PSi) prepared by anodic etching has demonstrated high efficiency room temperature visible photoluminescence [2,3]. Reasonably efficient PSi-based light-emitting devices (LEDs) have been fabricated (external power efficiency > 0.1% [4] ), however the stability of such LEDs continues to be a serious problem for practical applications because the efficiency decreases drastically during the first hour of operation [4,5;]. In addition, the as-anodized material cannot be integrated into conventional silicon process technology because of its extreme reactivity and inherently fragile structure. Partial oxidation of porous silicon in a dilute oxygen ambient produces silicon nanoclusters within an oxide matrix, or silicon-rich silicon oxide (SRSO). This material exhibits appropriate light-emitting and carrier transport properties and is compatible with conventional processing techniques. * also Department of Microelectronic Engineering, Rochester Institute of Technology, Rochester, NY 14623
"also Laboratory for Laser Energetics, Dep;rtment of Physics & Astronomy, and The Institute of Optics, University of Rochester, Rochester NY 14627
705 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
We have previously reported [6,7] on a surface-emitting SRSO-based LED which has characteristics among the best reported in silicon-based technology [4,8] with respect to electroluminescence (EL) efficiency, operating threshold conditions and frequency response, and demonstrates a significant improvement over porous silicon based device structures with respect to device stability. In contrast to porous silicon, the active SRSO layer satisfies several critical microelectronic material processing requirements including tolerance to thermal processing (T-10000 C) and chemical resistance. A simple optoelectronic circuit which integrates the SRSO-based LED with a bipolar driver transistor has now been designed and fabricated, and test results verify its compatibility with the IC process. Al
EXPERIMENTAL
LED Fabrication
n+ select poly
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polysilicon
, mesoporous Si
The fabrication sequence for the SRSO-based LED is now briefly discussed (for a more detailed description of the yp layer specific processing conditions refer to [6] ). p cSpbackside Ay A 10Kcm p-type crystalline silicon wafer with a heavily doped p+ surface layer is anodized in an HF/ethanol solution. The p+ Fig. 1. Cross-section of the SRSO-based LED multilayer region is transformed into a mesoporous structure including the aluminum contact, n+ polysilicon layer (porosity - 40%), whereas the cathode, mesoporous Si transition layer, and SRSO active underlying p-type silicon is transformed into layer. Also included is a p+ layer and aluminum contact to the backside of the crystalline Si substrate. a nanoporous silicon layer (porosity 75-80%) which extends 0.5-1.0ltm into the substrate. A dilute oxygen anneal (10% 02 in N2) at 800-900'C is then performed to trans
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