Surface passivation for InAs and InAs/InAsSb T2SL photodetectors

InAs has drawn a lot of attention for high performance transistors, optical applications, and chemical sensing due to its narrow band gap and very high near surface electron mobility. It has been also widely used for type II superlattice and avalanche photodiode arrays and is one of the standard materials used for mid-wavelength infrared (MWIR) photodetectors. One technical challenge for InAs related applications is to overcome the highly leaky InAs and passivation interface and achieve high stability surface passivation layer over InAs. The successful development of a new surface passivation process that is suitable for Teledyne Judson Technology (TJT) InAs mesa photodetectors was reported in previous work. This passivation did not cause InAs detector performance degradation and showed good stability and process compatibility with the detector assembly/packaging processes. In this paper, the extensive study of key process parameters optimization, including junction depth, trench height, passivation layers thickness, surface roughness and thinning process tailoring, will be covered. Characterization on InAs and InAs/InAsSb T2SL MESA and passivation quality were then performed. Optical and electrical characterizations of detector performance have been conducted, and the results have been analyzed and compared with TJT conventional InAs products, including dark current, shunt resistance, spectral responsivity, QE, and spatial photo-response uniformity over various temperatures. Passivation surface tension, which is essential for device surface condensation control and long-term stability, has also been investigated and compared for different processes. Wafer level and packaging level yield comparison between this newly development vs. process of record (POR) was also reported. By optimizing the passivation process, the significantly improved device performance stability and yield have been achieved and presented in this paper. In addition, the new surface passivation layer also serves as an anti-reflection coating (ARC) that enhances the InAs as well as the InAs/InAsSb T2SL detector spectral response and QE when optimized to the wavelength of interest for frontside illuminated detectors. Broad band ARC design for InAs/InAsSb T2SL backside illuminated focal plan array under TJT development has also been performed and discussed in this work.