MCT ALLOY: A HIGH PERFORMANCE VERSATILE IR DETECTOR MATERIAL
Due to its band gap tunnability the HgCdTe alloy covers the entire IR range and provides an unprecedented degree of freedom in infrared detector. The favorable recombination mechanisms and the high quantum efficiency of HgCdTe alloy allow the highest detectivity from short wavelength to very long wavelength.
The nearly ideal position of HgCdTe material for IR detection is conditioned by four key features:
- extremely small change of lattice constant with composition that makes possible to grow high quality layers and heterostructures
- tailorable energy band gap over 1-30 µm range
- large optical coefficients that enable high quantum efficiency
- favorable inherent recombination mechanisms that lead to high operating temperature
Since the first report on HgCdTe in 1959 by the Royal Radar Establishment, HgCdTe has successfully fought off major IR detection challenges. From the first photodiode processed by the French researchers Verie and Granger in 1965, the pioneering work performed by the Societe Anonyme de Telecommunication (France) in the mid-1970s, to nowadays very large focal plane array, HgCdTe detectors performances have never been surpassed. Thanks to thirty years of joined studies of Sofradir and CEA-LETI, remarkable improvements have been carried out for CdTe substrates and HgCdTe layers growth, leading to very large substrates and high quality liquid phase epitaxy layers. The same progress holds for diode process quality and passivation. All this work maintains HgCdTe as a major leader for the third IR detector generation (smaller pitches, higher operating temperatures, multi-color and HD formats), and preparing the fourth generation with avalanche photodiodes and extrinsic photodiodes for above 150K IR detection.