**1. Introduction**

The importance of infrared (IR) radiation technology results from the prevalence of infrared radiation. Infrared is invisible to the human eye radiant energy emitted by any object at temperature above absolute zero. Of particular importance is the spectrum of objects at temperature close to the average temperature of the Earth. It provides the comprehensive

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information about their position in space, temperature, surface properties, as well as informa‐ tion about the chemical composition of the atmosphere through which the radiation is trans‐ mitted.

All information carried by the infrared radiation can be read and processed by suitable sensors (detectors) that transform infrared energy into other forms, directly and easy to measure. The sensors used to detect infrared radiation are usually equipped with two types of detectors: thermal detectors and photon detectors.

At present, the technology of the mid- (MWIR, 3–8 μm) and long-wave (LWIR, 8–14 μm) infrared radiation is mainly connected with photon detectors, designed on the basis of complex semiconductor materials, such as mercury cadmium telluride (HgCdTe) or indium gallium arsenide (InGaAs). The incident radiation is absorbed within the material by interaction with electrons, and the detector signal is caused by changes of the electric energy distribution. They exhibit both perfect signal-to-noise performance and a very fast response. But to achieve this, the present photon detectors require cryogenic cooling. Cryogenic cooling creates the cost and inconvenient limitations, especially in civil applications.

Thus, higher operation temperature (HOT) condition is one of the most important research areas in infrared technology. The development of a new detector's architecture has been driven by applications requiring multispectral detection, high-frequency response, high detectivity, small size, low weight and power consumption (SWaP), and finally HOT condition. Significant improvements in the reduction of the dark current leading to HOT condition have been achieved by the suppression of Auger thermal generation [1]. In practice, most of the HgCdTe Auger suppressed photodiodes are based on complex graded gap and doping multilayer structures, complicated to grow in terms of technology. The P+ πN<sup>+</sup> or N<sup>+</sup> νP<sup>+</sup> device structures with a combination of exclusion (P+ /π or N<sup>+</sup> /ν) and extraction (N<sup>+</sup> /π or P+ /ν) junctions have demonstrated the suppression of Auger mechanisms by reducing the absorber carrier density below thermal equilibrium in reverse bias condition. A recent strategy to achieve HOT detectors includes simple nBn (B: barrier layer) barrier structures [2].

This chapter exhibits the fundamental properties of HgCdTe semiconductors and relates those material parameters that have successful applications as an IR barrier detector alloy. It presents different barrier HgCdTe structures in terms of dark current. The intent of this chapter is to concentrate on a barrier device approach having the greatest impact on IR industry develop‐ ment today.
