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0952-F02-03

Multispectral Photonic Crystal Photo Sensor Xiaochen Sun, Juejun Hu, Ching-yin Hong, Jeff Viens, Rupa Das, Anuradha M. M. Agarwal, and Lionel C. Kimerling MIT, Cambridge, MA, 02139

ABSTRACT A novel photo sensor pixel using a one-dimensional (1D) photonic crystal structure incorporating photoconductive layers has been realized. The fabricated device exploits mode discrimination to provide simultaneous multispectral photo sensing capability. Resonant cavity enhancement (RCE) design allows the use of very thin photoconductive layer to achieve dramatically suppressed shot noise, as well as high quantum efficiency. Low cost amorphous silicon is used to be photoconductive material and the simply fabrication process is completely CMOS-compatible. Detectivities as high as 2.6×1010 cmHz1/2W-1 and 2.0×1010 cmHz1/2W-1 at the two pre-selected wavelengths, 632nm and 728nm, were achieved, respectively.

INTRODUCTION Applications such as multi-chemical sensing, biological sensing, multispectral imaging and spectroscopy call for specialized photo sensor that are capable of selectively sensing specific wavelengths simultaneously, namely multispectral photodetection. Traditionally, multispectral capability has been achieved by several methods, including spatial registration (color filter array) [1,2], temporal registration (mechanical filter wheel) [3], tandem structure [4] or quantum well photodetectors [5,6]. The first two methods complicate the pixel design and raise the issue of system reliability. In a tandem detector, the top detector serves as a passband filter for the bottom detector. The problem associated with this design is that only certain spectral bands are accessible due to limited material choices. Despite their high leakage current, quantum well detectors are capable of multispectral detection by varying applied bias. However, the time multiplexing involved prohibits simultaneous detection of different wavelength within a single pixel [7]. In addition, all the aforementioned methods necessitate the engineering of latticematched single-crystalline materials in order to reduce dark current, which requires high-cost and complicated material growth facilities such as Molecular Beam Epitaxy (MBE) or Metal-Organic Chemical Vapor Deposition (MOCVD). In this letter, we present a designed and fabricated photonic crystal structure incorporating photoconductive layers to achieve simultaneous multispectral sensing. This photoconductor pixel exploits resonant cavity enhancement (RCE) for multispectral capability, high quantum efficiency, and dramatically suppressed shot noise. As we know, a quarterwavelength stack (one-dimensional photonic crystal structure) supports a photonic bandgap, all wavelengths within the range of which are highly reflected when coming through the stack. While standing wave patterns (defect modes) form at resonant wavelengths when halfwavelength layers (defect layers) are present. The number of the resonant wavelengths is equal

to the number of the defect layers. By tuning the thicknesses