Uncooled photovoltaic Hg 1-x Cd x Te LWIR detectors

Abstract

We report an advanced Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te photovoltaic detector based on monolithic Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te heterostructure with 3-dimensional architecture. It consists of a narrow gap, p-type Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te small size (approximately equals 10x10x7 micrometers ) absorber of infrared radiation buried in a graded gap Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te layer surrounding absorber and heterojunction contacts obtained by selective doping of the graded gap Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te layer surrounding the absorber region. The heterostructure is passivated with a ZnS layer and coated with contact metallization to n<SUP>PLU</SUP> and p-type regions. The device is supplied with 50x50 micrometers immersion microlens formed directly in the CdZnTe substrate. These two layers also play a role of a mirror that improves quantum efficiency for weakly absorbed infrared radiation. In addition, the mirror eliminates backside incidence of thermal radiation, which prevents generation of dark current. The design of the device is optimized to achieve the best compromise between requirements of good absorption and collection efficiency; low thermal generation; and low parasitic impedance. Test devices have been prepared using the modified isothermal vapor phase epitaxy of Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te on profiled CdZnTe substrates, negative epitaxy of Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te to widen band gap of surface regions, selective doping, multiple chemical etching and ion milling, vacuum deposition of dielectric and metal layers.