MESA Etch and Surface Passivation for InAs Photodetectors - Optical, Electrical Performance, and Stability Improvement

InAs is a very attractive material for high performance transistors, optical applications, and chemical sensing. However, it has been very challenging to achieve high stability surface passivation layer over InAs due to the very high leaky InAs and passivation interface. Various passivation method attempts in the past were not successful at TJT as they all caused significant degradation of InAs detector performance. As a result, no surface passivation has been used for TJT standard InAs photodetectors until now. In this paper, we report for the first time a successful development of a new surface passivation process that is suitable for TJT InAs mesa photodetectors. This passivation did not cause InAs detector performance degradation and showed good stability and process compatibility with the detector assembly/packaging processes. Etching methods have been evaluated and applied to form InAs MESA photodiodes. Afterwards, multiple paths for surface treatment and passivation, including wet treatment, Polymer Encapsulation, Atomic Layer Deposition and Thermal Evaporation, have been compared and applied to the as developed photodiodes. Extensive characterization on InAs MESA and passivation quality were then performed. Key control factors, including surface treatment, MESA height, junction depth, etc., have been studied and optimized through design of experiment (DOE). Optical and electrical characterizations of detector performance have been performed and analyzed, including dark current, capacitance, shunt resistance, spectral responsivity and QE, and spatial uniformity over various temperatures. By optimization of passivation process, the significantly improved device performance stability has 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 detector spectral response and QE when optimized to the wavelength of interest.