Dual-Band MW/LW IRFPAs made from HgCdTe grown by MOVPE

Abstract

This paper describes the design, fabrication and performance of dual-band MW/LW infrared detectors made from HgCdTe (MCT) grown by Metal Organic Vapour Phase Epitaxy (MOVPE). The detectors are staring, focal plane arrays consisting of HgCdTe mesa-diode arrays bump bonded to silicon read-out circuits. Each mesa has one connection to the ROIC and the bands are selected by varying the applied bias. Arrays of 320x256 pixels on a 30 μm pitch have performed exceedingly well. For example, arrays with a cut-off wavelength of 5 μm in the MW (mid-wave) band and 10 μm in the LW (long-wave) band have median NETDs of 10 and 17 mK and defect levels of 0.3% and 0.05%, in the MW and LW bands respectively. Interestingly the LW defect level is often lower than the MW defect level and the defects are not correlated; i.e. a pixel that is defective in the MW band is usually not defective in the LW band. Arrays of 640x512 pixels on a 24 μm pitch have been developed. These use a read-out integrated circuit (ROIC) that has two capacitors per pixel and the ability to switch bands during a frame giving quasi-simultaneous images. The performance of these arrays has been excellent with NETDs of 14mK in the MW band and 23mK in the LW band. Dual band-pass filters have been designed and built into a detector.