Advanced High Operating Temperature Mid-Wave Infrared Sensors

High sensitivity HgCdTe infrared arrays operating at 77K can now be tailored in a wide range of wavelengths. However, the cooling requirements make them bulky and unsuitable for many DOD applications. We propose two novel approaches to increase their operating temperature. In the first approach, we will demonstrate p-d-n equilibrium HgCdTe detectors. Because of the lack of symmetry between the valence and conduction bands in HgCdTe, the lifetimes in d-type material are higher than those in n-type layers. The challenge of implementing a p-d-n HgCdTe detector is to obtain low p-type doping in the absorber region. Arsenic will be introduced by a novel technique based on implantation and diffusion by thermal annealing. In the second approach, p-d-n devices developed in the first approach will be operated under non-equilibrium conditions. In non-equilibrium operation the minority carriers are extracted to one side of the active area of a detector and the contact to the other side prevents their replenishment. As a consequence, the carrier concentration is decreased dramatically. This leads to increases in recombination lifetimes, dynamic impedances and detectivities. To implement these two approaches, we propose to use HgCdTe infrared materials grown by molecular beam epitaxy (MBE) directly on large area (3-5") silicon substrates with CdTe buffer layers.