Large-area IR negative luminescent devices

Negative luminescent (NL) devices, which to an IR observer appear colder than they actually are, have a wide range of possible applications, including for use as IR sources in gas-sensing systems and as thermal radiation shields in IR cameras. Additionally, these devices can be used as calibration sources for very large IR focal plane arrays and have many potential advantages over conventional calibration sources, including high-speed operation (for multi-point correction) and low power consumption. For many of these applications a large area ∼1cm2 device which displays an, as large as possible, apparent temperature range is required. However, significant currents are required to reduce the carrier concentrations to the levels needed for maximum dynamic range. The authors have therefore used a novel micromachining technique to fabricate integrated optical concentrators in InSb/InAlSb and HgCdTe NL devices. Smaller area diodes can then be used to achieve the same absorption (e.g. for InSb an area reduction of 16 is possible) and the required currents are thus reduced. Recent results are presented from a large area ∼0.862 medium wavelength (MW) device incorporating integrated optical concentrators. The reverse saturation current of the device was measured to be ∼2.3 A/cm2, which is significantly smaller than the value of ∼9 A/cm2 reported previously for similar devices without optical concentrators. In addition, the large apparent temperature drop of the device ∼20K for a detector of cut-off 6.5µm when under reverse bias, coupled with its large size, mean that this device would be appropriate for use as a calibration source for IR imagers.