# Trends in Performance Limits of the HOT Infrared Photodetectors
## 1 Introduction  
HgCdTe takes the dominant position in infrared (IR) detector technology. This material has triggered the rapid development of the three \"detector generations\" considered for military and civilian applications and briefly described in the caption of Figure 1. IR detector technology combined with fabrication of epitaxial heterostructure [by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD)] and photolithographic processes revolutionized the semiconductor industry, thus enabling the design and fabrication of complex focal plane arrays (FPAs). Further their development will relate to implementation of fourth generation staring systems, which the main features are to be: high resolution (pixels \(>10^{8}\)), multi-band detection, three-dimensional readout integration circuits (3D ROIC), and other integration functions such as polarization/phase sensitivity, better radiation/pixel coupling or avalanche multiplication. The first three generations of imaging systems primarily rely on planar FPAs. Several approaches to circumvent these limitations, including bonding the detectors to flexible or curved molds, have been proposed [1]. Evolution of fourth generation is inspired by the most famous visual systems, which are the biological eyes. Solution based on the Petzval-matched curvature allows the reduction of field curvature aberration. In addition, it combines such advantages as simplified lens system, electronic eye systems and wide field-of-view (FOV) [2, 3]. The colloidal quantum dot (COD) [4] and 2D layered material [5] photodetectors fabricated on flexible substrates exhibit the potential to circumvent technical challenges in the development of the fourth generation IR systems. The need for cooling considerably limits more widespread use of IR technology. There are significant attempts to decrease system size, weight, and power consumption (SWaP) to limit IR system's cost and to increase the operating temperature. The invention of microbolometer array was a milestone step in development of IR cameras operating at 300 K. However, microbolometers belong to the class of thermal detectors with limited response time--typically in millisecond range and could not be used in the multiband applications. To omit this limitation, further efforts are directed to increase operating temperature of photon detectors. Initial efforts in development of the high operating temperatures (HOT) photodetectors were focused on HgCdTe photoconductors and photoelectromagnetic detectors [6]. Many concepts have been implemented and tested to improve the performance of IR photodetectors operating at near 300 K and compiled in References [7; 8; 9; 10]. In addition to photoresistors and photodiodes, three other types of IR detectors can operate at near 300 K: magnetic concentration detectors, photoelectromagnetic (or PEM) detectors and Dember effect detectors. The HgCdTe non-equilibrium devices such as the Auger suppressed excluded photoconductors and extracted photodiodes require significant bias what creates excessive 1/f noise. Figure 1: The history of IR detectors and systems development. Four generation systems for military and civilian applications can be considered: first generation (scanning systems), second generation (staring systems—electronically scanned), third generation (staring systems with large number of pixels and two-color functionality), and fourth generation (staring systems with very large number of pixels, multi-color functionality, 3D ROIC, and other on-chip functions; e.g., better radiation/pixel coupling, avalanche multiplication in pixels, polarization/phase sensitivity. Up till now, mainly HgCdTe and Sb-based III-V ternary alloys including barrier detectors with type-II superlattices (T2 SLs: InAs/GaSb and InAs/InAsSb) have been considered for HOT IR photodetectors. The recently published monograph covers this topic for III-V material systems [11].