HgTe-CdTe superlattice infrared detectors

Abstract

A great deal of interest has developed in the use of superlattices as infrared materials. The infrared superlattice to be discussed is the one formed by laying down repeatedly a layer of Hg x 1Cd1- x 1 Te followed by a layer of Hg x 2Cd1- x 2 Te with x1 ≠ x2. To date, most of the research has been for the case when x1 = 1 and x2 = 0. The theoretical studies have indicated that superlattices could provide an interesting solution to a number of problems that exist with the alloy materials. For example, the band gap of the superlattice is adjusted by adjusting the thickness of the HgTe and CdTe layers, in contrast to the alloy, where the relative concentration of the Hg and Cd are used to control the gap. Particularly in the case of narrow band gap systems, this form of control seems easier to accomplish. In the superlattice, the direct relationship between the effective mass and the band gap is broken making possible the suppression of tunneling, leakage currents even in very narrow band gap materials. These superlattices have been successfully fabricated. Current research is emphasizing the near band gap properties and structural characterization of these superlattices. In this presentation, we make a critical examination of what we know about these properties and the degree to which there is agreement between theory and experiment.