CdTe–HgTe Heterostructures

The heterostructures described here were prepared by solid-state diffusion from a mixture of CdTe and HgTe powders into a wafer of single-crystal CdTe. The composition profiles as measured with an electron-beam microprobe show that 100 μ wide transition regions can be achieved. These profiles are consistent with published results on diffusion between bulk HgTe and bulk CdTe. Increasing the proportion of HgTe in the powder shifts the optical absorption edge from a wavelength of 0.8 μ (the value for bulk CdTe) to beyond the 15 μ limit of the measuring instruments. The photoelectromagnetic (PEM) effect shows a fairly flat spectral sensitivity for wavelengths between 1 and 5 μ. The photovoltaic response shows an anomalous exponential dependence on the photon energy, believed to be due to an undesirable p-n junction caused by cadmium vacancy formation. Theoretical models are derived for both effects.