Ion implantation study of Be in InSb for photodiode fabrication


Josh Duran

Date of Award


Degree Name

M.S. in Electro-Optics


Department of Electro-Optics and Photonics


Advisor: Andrew M. Sarangan


InSb p-n junction detectors from bulk crystals are commonly utilized for mid-wave infrared (MWIR) focal-plane arrays (FPAs) because of their high quantum efficiency and well-established fabrication methods. The doping profiles of these detector structures are commonly defined by thermal diffusion techniques because it is an economical and repeatable fabrication process. The resulting impurity profiles have a characteristic shape determined by Fick's diffusion laws. In order to realize structures that are more complicated than simple PN junctions, like APDs, alternative methods of introducing and controlling impurities need to be developed, especially when high and low doping concentrations at specific depths beneath the surface are needed. Another technique that could maintain similar cost effectiveness and repeatability as thermal diffusion while providing greater control over the doping profile is ion implantation. This is well-developed for silicon, but less developed for InSb. Accurate modeling of the doping profile shapes and depth are important for transitioning detector designs to properly functioning devices. SRIM modeling software is used to predict the doping profiles of implanted Be ions into n-type InSb substrates. To test the accuracy of this software, implantations of varying energy were performed. After implantation, the doping profiles of these samples were measured using secondary ion mass spectrometry (SIMS) before and after a rapid thermal anneal. It was found that Be ions do not diffuse within the repeatability tolerance of the SIMS measurement technique. The SIMS results also revealed a highly oxidized InSb surface. This oxidized surface should be considered during the fabrication process. Spreading resistance profile measurement is made on an annealed Be implanted sample. P on N carrier concentration is verified by this measurement which suggests successful activation during anneal. A process for fabricating InSb photodiodes with ion implantation is developed and reported. The fabrication process has not been optimized for performance, but verification of functioning detectors is established with dark current and spectral response measurements. These measurements verify successful photodiode operation.


Ion implantation, Infrared detectors, Photodiodes Design and construction, Optical detectors Design and construction

Rights Statement

Copyright 2011, author