HgTe-HgCdTe superlattice photodetector has high response in LWIR

A superlattice of mercury telluride-mercury cadmium telluride (HgTe-HgCdTe) contains alternating layers of the two materials only nanometers thick; when used for IR photoconductive optical detectors, such a superlattice can have high absorption and good control of the cut-off wavelength. But until now there has been little data on the fabrication and use of such detectors in the longwave IR (LWIR). Researchers at the University of Western Australia (Crawley, Australia) and the Physikalisches Institut der Universität Würzburg (Würzburg, Germany) have fabricated two different examples of such detectors by molecular-beam epitaxy, comparing them to a non-superlattice detector of HgCdTe used as a control.

The differences in the two superlattice detectors were in the number of layers (120 versus 100) and the details of the elemental proportions in the layers under test. one of the superlattice detectors (Q1104) showed higher spectral quantum efficiencies as a function of thickness compared to the simple HgCdTe detector, partially because its absorption coefficient was more than four times higher. The spectral photoresponse of the other superlattice detector extended out well past 12 μm, compared to the less than 11 μm cutoff of the control. Contact John Dell at [email protected].