This article reviews the history, the present status and possible future developments of HgCdTe ternary alloy for infrared (IR) detector applications. HgCdTe IR detectors have been intensively developed since the first synthesis of this material in 1958. This article summarizes the fundamental properties of this versatile narrow gap semiconductor, and relates the material properties to its successful applications as an IR photoconductive and photovoltaic detector material. An emphasis is put on key developments in the crystal growth and their influence on device evolution. Competitive technologies to HgCdTe ternary alloy are also presented. Recent advances of backside illuminated HgCdTe heterojunction photodiodes have enabled a third generation of multispectral instruments for remote sensing applications and have led to the practicality of multiband IR focal plane array technology. Finally, evaluation of HgCdTe for room temperature long wavelength IR applications is presented. (Some figures in this article are in colour only in the electronic version)

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HgCdTe infrared detector material: history, status and outlook

The band gap and the intrinsic carrier concentration in a semiconductor are important material parameters needed in the interpretation of various experimental and theoretical data. In the present work, empirical expressions for both the parameters as a function of alloy composition x and temperature are proposed for GaxIn1−xAs. The calculated results for band gap are in close agreement with the available data, while the same for intrinsic concentration give fair agreement with the data at the two ends of the alloy composition.

Empirical expressions for the alloy composition and temperature dependence of the band gap and intrinsic carrier density in GaxIn1-xAs

Intrinsic infrared detectors

Ultimate performance of infrared photodetectors and figure of merit of detector material

Near room-temperature IR photo-detectors

Intrinsic carrier concentration in Hg1−xCdxTe is calculated as a function of temperature and composition using the Kane nonparabolic approximation for band structure and recent measurements of the heavy hole mass mh and energy gap Eg. An expression fitted to these calculations is: ni[5.585−3.820x+1.753(10−3)T −1.364(10−3)xT] ×(1014)E3/4gT3/2 exp(−Eg/2kbT). The fit of this approximation is within 1% of the calculated ni for the range Eg>0, 50<T<300 K and x<0.7. It is also within 15% of experimental ni obtained from Hall measurements.

J. L. Schmit

Papers

Calculation of intrinsic carrier concentration in Hg1−xCdxTe