Amorphous and nanocrystalline p-i-n Si and Si,Ge photodetectors for structurally integrated O2 sensors

Recent efforts to develop compact, field-deployable photoluminescence (PL)-based chemical and biological sensors have focused on structurally integrating an array of organic light emitting device (OLED) pixels, which serve as the excitation source, with a sensing film, and a thin-film photodetector (PD). To that end, VHF and ECR were used for fabricating and comparing amorphous and nanocrystalline p-i-n Si- and Si,Ge-based PDs for monitoring O-2, which is preferably determined by monitoring the PL decay time, rather than the PL intensity, of the sensing film. This approach eliminates the need for frequent sensor calibration and, as pulsed OLED excitation is employed in this mode, the need for optical filters, which lead to bulkier sensors. Therefore, the development of the PDs also focused on increasing their speed, and understanding the factors affecting it, such as the device structure and boron diffusion during growth from the p+ to the i layer in p-i-n PDs. Incorporating a SiC buffer layer at the p+/i interface and a superstrate structure, where the p+ layer was grown last, increased the speed. The effects of Ge, p+ layer thickness, nanocrystallinity, defect states, and the illumination wavelength on the speed are also discussed. (C) 2007 Elsevier B.V. All rights reserved.