Speaker
Description
Various detector concepts based on gallium arsenide have been developed and characterized for hard X-ray applications. Recently, a 3D imager with capacitively coupled GaAs based avalanche photodiode and cross-delay lines (APCDL) was reported for hard X-ray photon detection [1]. This hybrid system is a promising imager offering temporal and spatial resolutions less than tens of picoseconds and hundreds of micrometers, respectively. In this report, we present results on formation of single-sided ohmic contacts and reduction of leakage current in GaAs p-i-n photodiodes designed for the APCDL hard X-ray imager. Actually, the obtained results are also applicable to other types of GaAs based photodetectors, where contacts are formed on one side, while the opposite side serves as a photoactive surface. The studied photodiode was grown by molecular beam epitaxy. After mesa structure fabrication, Cr/Au metals were deposited by E-beam evaporation to form single-sided contacts. The prepared sample is depicted in Fig.1. It was found that the ohmic contacts are formed on both the highly doped p+ layer and low doped (1×1016 cm-3) n-type layer by annealing the sample at 325 0C for 2 min in a nitrogen atmosphere. Besides ohmic contacts, a blocking contact was evaporated after deposition of an isolating SiO2 layer. This contact is used to prevent the flow of shunt current by applying the same potential as that on the anode (see Fig. 1). The reduction of dark current by using the blocking contact was demonstrated through current-voltage measurements. Additionally, the capacitive-voltage characteristic and laser responsivity of fabricated detector were investigated.
References
[1] N. Lusardi et al., "Time-Resolved 3D Imaging with Capacitively Coupled GaAs SAM-APD and Cross-Delay Lines for Hard X-Ray Photon Detection," 2024 IEEE Nuclear Science Symposium (NSS), Medical Imaging Conference (MIC) and Room Temperature Semiconductor Detector Conference (RTSD), Tampa, FL, USA, 2024, pp. 1-2.
