Infra red arrays

The IR sensing epitaxial structures will consist of LWIR-SLS detectors grown on GaAs. WP challenges will be achieving high material quality with high uniformity, and the growth challenges associated with this. Growth conditions will be optimized, and high performance detectors will be designed before model characterisation.

The IR sensing epitaxial structures will consist of LWIR-SLS detectors grown on GaAs. Achieving high material quality (high photoluminescence intensity, low surface roughness) with high uniformity is a growth challenge due to the ~7.8% lattice mismatch between GaSb and GaAs. The growth conditions (growth temperature, As and Sb flux, and shutter sequence) will be optimized, moving from 100 mm wafer to 150 mm.

High performance LWIR-SLS detectors will be designed using accurate simulation tools, based on the k.p model with the Envelope Function Approximation (EFA) for SLS material properties and on Technology Computer Aided Design software for device design. The model developed will be qualified against measured performance.

Fabrication of photodiode arrays, from the epitaxial SLS layers, will use Inductively Coupled Plasma (ICP) deep etching for isotropic profiles. It will first be optimized on single-pixel photodiode and then extended to detector arrays. The required passivation – such as SiO2 or Si3N4 – to reduce/suppress surface leakage currents will have to be compatible with subsequent processing and integration up to the camera level.

Electrical and electro-optical characterizations will be performed on small areas before hybridization. The system will consist of a hybrid infrared FPA interconnecting a detector array and readout integrated circuit (ROIC) using indium bump bonding for the hybrid packaging. This will be mounted on a ceramic leadless chip carrier, wire-bounded and loaded in a cryostat for optical testing to evaluate dark current, quantum efficiency and uniformity.