A novel multi-Heterojunction HgCdTe long-wavelength infrared photovoltaic detector for operation under reduced cooling conditions

A new multi-heterojunction (n) under bar(+) pi (p) under bar photovoltaic infrared photodetector is presented. The device has been developed specifically for operation at elevated temperatures (>200 K) for detection of infrared radiation in the mid- and long-wavelength range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long-wavelength infrared photovoltaic detectors when operated near room temperature. Analysis indicates that practical devices with properly optimized multiple heterojunction layers are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapour phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling and angled thermal evaporation for contact metal deposition. These multi-junction (n) under bar(+) pi (p) under bar HgCdTe heterostructure devices exhibit performances comparable to, or better than, existing long-wavelength photoconductors and photoelectromagnetic detectors operated under the same conditions. A typical D* of optically immersed multiple heterostructure photovoltaic detectors of approximately 10(9) cm Hz(1/2) W-1 can be achieved at a signal wavelength of 10.6 mu m and for operation at 230 K.