<title>Isothermal vapor phase epitaxy as a versatile technology for infrared photodetectors</title>

Abstract

We report here the use of isothermal vapor phase epitaxy to grow 3D Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te heterostructures for photoconductive, photovoltaic and photoelectromagnetic infrared detectors operated at near room temperatures. A reusable two-zone atmospheric pressure growth system has been developed.the system makes it possible not only to grow epilayers but also to perform in situ other processes such as high temperature annealing to control the compositional grading, the low temperature annealing for reduction of native acceptor concentration, and doping with foreign impurities. The required various composition profiles have been theoretically predicted and then implemented changing the temperature and mercury pressure during growth and subsequent thermal treatment. In addition, post-growth etching, substrate shaping, selective epitaxy, and negative epitaxy have been used to achieve 3D band gap profiles. The photoconductors were based on lightly p-type doped epilayers. Low diffusion length, weak absorption of radiation and a very low junction resistance makes it difficult to obtain useful performance of longwavelength photovoltaic devices operating at near room temperature. This was overcome with development of multiple heterojunction photovoltaic devices in which short elements were connected in series. To improve the performance of any type of heterostructure photodetector, monolithic optical immersion has been used. Detectivities as high as 1 X 10<SUP>8</SUP> cmHz<SUP>1/2</SUP>/W and 1 X 10<SUP>9</SUP> cmHz<SUP>1/2</SUP>/W were obtained at (lambda) equals micrometers and temperatures of 300 K and 220 K, respectively.