Solar-Blind AlGaN-based Schottky Photodiodes With High Detectivity and Low Noise
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Solar-Blind AlGaN-based Schottky Photodiodes With High Detectivity and Low Noise Necmi Biyikli a) and Orhan Aytur Department of Electrical and Electronics Engineering, Bilkent University, Bilkent Ankara 06533, TURKEY
Ibrahim Kimukin, Turgut Tut and Ekmel Ozbay Department of Physics, Bilkent University, Bilkent Ankara 06533, TURKEY
Abstract We report on the design, fabrication and characterization of solar-blind Schottky photodiodes with high detectivity and low noise. The devices were fabricated on n/n+ AlGaN/GaN hetero-structures using a microwave compatible fabrication process. Using Al0.38Ga0.62N absorption layer, true solar-blind operation with a cutoff wavelength of ~274 nm was achieved. The solar-blind detectors exhibited < 400 fA dark current in the 0-25 V reverse bias regime, and a maximum responsivity of 89 mA/W around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6x1012 cmHz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3x10-29 A2/Hz at 10 KHz.
1. Introduction Photodetectors that operate only in the λ < 280 nm spectrum are named as solar-blind detectors due to their blindness to solar radiation within the atmosphere.1 Solar-blind photodetectors are essential components for a number of applications including missile plume detection and missile tracking, flame/engine control, chemical/biological agent sensing, UV astronomy, and ozone layer monitoring. AlxGa1-xN-based photodetectors potentially offer significant advantages over the current photomultiplier tube and silicon-based solar-blind detector technology in terms of size, complexity, cost, robustness, stability, power demands, and bandwidth.2 Moreover, its intrinsic solar-blindness (for x ≥ 0.38) and the ability of operation under harsh conditions (high temperature and high power levels) due to its wide band-gap makes AlxGa1-xN-based photodetectors attractive for highperformance solar-blind detection applications. Several research groups have demonstrated successful solar-blind operation with AlxGa1-xN photodetectors using photoconductive,3,4 p-i-n,5-14 metal-semiconductor-metal (MSM),15-16 and Schottky17-20 detector structures. Cut-off wavelengths (λc) as short as ∼225 nm, a UV/VIS rejection over 5 orders of magnitude along with responsivities as high as 0.12 A/W at 232 nm were reported using a Al0.7Ga0.3N p-i-n detector structure.6,11 Al0.5Ga0.5N MSM photodiodes with a noise equivalent power (NEP) as low as 30 fW
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at 280 nm and detectivity of 2.5x1013 cmHz1/2/W correspond to the best noise performance achieved for AlGaN-based solar-blind detectors.15 Dark currents less than 2 pA at 30 V reverse bias and a 3-dB bandwidth of 100 MHz was reported for a Al0.4Ga0.6N MSM structure.16 Al0.35Ga0.65N p-i-n photodiodes on SiC substrates with low leakage currents were also successfully demonstrated.12 When compared with p-i-n photodiodes, AlGaN Schottky photodiodes have several advantages. Growth of p-type doped AlGaN layers and formation of low resistance p+ ohmic contacts are tw
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