1Institute of Microelectronics and Tsinghua National Laboratory for Information Science and Technology, Tsinghua University, Beijing 100084 2Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083
Abstract：To measure small particles in clouds without the optical amplification system, a new type of p-i-n photodetector linear array with 128 diode units altogether is designed and realized. In each die, there are two rows of photodiode line array, and each row has 64 photodiodes. Every photodiode has a size of 100 μm × 100 μm with an individual output, and each of them is isolated by the trenches. The depth of them has the same thickness as that of the epitaxial layer, which is designed to be 30 μm to guarantee sufficient absorption of photons and leave a margin for the diffusion of p-type and n-type region. The detector has been tested with a laser whose wavelength was 650 nm and irradiance is 50 mW/cm2. The achieved photocurrent is 2 μA. Hence, the current responsivity is about 0.4 A/W, and the external quantum efficiency is 76.45%. The dark current is less than 600 pA. Both of the sufficient absorption of photons and low dark current are achieved by utilizing the thick epitaxial intrinsic layer. Low interference of adjacent photodiodes is also guaranteed by the trenches around the photodiodes. With the obtained performance, the photodetector can be used to measure the diameter of precipitation particles in clouds. Therefore, rainfall can be judged based on the diameter of particles.
[1] Watanabe Y and Nishizawa J 1950 Jpn. Patent205 68 [2] Renker D and Lorenz E 2009 J. Instrum.4 04004 [3] Knollenberg R G 1970 J. Appl. Meteorol.9 86 [4] Heymsfield A J and Knollenberg R G 1972 J. Atmos. Sci.29 1358 [5] Hauser D, Amayenc P, Nutten B and Waldteufel P 1984 J. Atmos. Oceanic Technol.1 256 [6] Loffler-Mang M and Joss J 2000 J. Atmos. Oceanic Technol.17 130 [7] Sch?nhuber M, Urban H, Baptista J P, Randeu W L and Riedler W 1994 Proceedings of Atmospheric Physics and Dynamics in the Analysis and Prognosis of Precipitation Fields (Rome, Italy) p 15 [8] McDonald J E 1958 Adv. Geophys.5 p 223 [9] Wallace J M and Hobbs P V 2006 Atmospheric Science: an Introductory Survey (Waltham: Academic press) [10] Houze R A, Hobbs P V, Herzegh P H and Parsons D B 1979 J. Atmos. Sci.36 156 [11] Green M A and Keevers M J 1995 Prog. Photovoltaics: Res. Appl.3 189
2014, Vol. 31 
