Optimization of quantum-well infrared detectors integrated with light-emitting diodes

The optimization of diffraction gratings for pixelless thermal imagers based on the epitaxial integration of a 9-μm quantum-well infrared photodetector (QWIP) and a near-infrared light-emitting diode (LED) is reported. It is found that the thickness of the reflecting layer deposited onto the grating should be carefully controlled to reach a good tradeoff between high infrared responsivity of the QWIP and reasonable external efficiency of the LED. In addition, on a non-optimized device we demonstrated thermal images with a temperature sensitivity below 100 mK and a noise equivalent temperature difference of 57 mK.