The starting point of the activities was the matching performance of a single element InGaAsSb detector, grown on a low cost GaAs substrate, reported by the University of Lancaster. GaAs substrates are low cost and available in large areas, making high pixel count arrays feasible, nevertheless resulting in a slightly lower InGaAsSb material quality. GaSb has been also used as second substrate material candidate: indeed it is easier to grow high quality layers on GaSb even though the bandgap of GaSb prevents to use it in 2D focal planes. Following the research conducted by the University of Lancaster, the interfacial Misfit (IMF) array technique was used to minimize the dislocations at the top side of the buffer layer, enabling the stress-free growth of the InGaAsSb sensing layer.
Several wafers have been processed – 4 nBn wafers (3 on GaAs and 1 on GaSb) and 4 PiN wafers (3 on GaAs and 1 on GaSb) – and the four most promising wafers were further tested at Xenics at room temperature and compared with commercial diodes’ performance (IQE) used as benchmark. Individual diode I-V characteristics in dark and illuminated conditions were measured on all samples: only two showed diode behavior but with very high currents in reverse bias, but almost no discernible response to light.
The most promising types of material, pin structure on n-GaAs (QM342) and n-GaSb (QM404) respectively, have been packaged in the Xenics-3501 ROIC together with the IQE sample diodes.