Series resistance optimization of high-sensitivity si-based VUV photodiodes

Recently, silicon ultrashallow p⁺ n photodiodes, fabricated by a pure boron deposition technology (B-layer diodes), were evaluated for detection in the Vacuum Ultra-Violet (VUV) spectral range from 115 nm to 215 nm wavelengths, where the attenuation length in silicon is only a few nanometers. Superior sensitivity in the order of 0.1 A/W in the whole VUV spectral range was reported. Next to the sensitivity, another important parameter of any photodetector is the response time, which is directly related to its series resistance. In this work a study of the relation between the sensitivity and the series resistance of the B-diodes is presented, supported by simulation results and optical/electrical experimental results. Moreover, practical methods for designing a high sensitivity VUV photodiodes while keeping a relatively low series resistance, are proposed. The experimental results demonstrate that by modifying the diode structure, the series resistance can be effectively reduced. At the same time, the B-layer diodes still maintain a high VUV sensitivity.