The state of the art of thin-film pyroelectric infrared (IR) detectors is reviewed covering device physics, material performance, micro-fabrication and device examples. Emphasis is given to special issues related to thin films, such as small heat capacities and the substrate influence on the pyroelectric properties. For the latter, an overview of the hitherto reported values is given. Examples of micromachined IR detectors based on pyroelectric thin films are described. The ultimate limit of micromachined thermal IR detectors is estimated for uncooled operation. It is concluded that the best pyroelectric thin films achieved to date are in principle sufficiently good to approach this limit, meaning that the present performance of pyroelectric thin-film focal plane arrays can still be improved by more than a factor of 10. A comparison of the different principles for IR detection shows that pyroelectricity is indeed one of the most competitive principles for uncooled IR detection. The major obstacle hindering quick industrialization is the fabrication complexity.

https://iopscience.iop.org/article/10.1088/0034-4885/64/10/203/pdf

Micromachined infrared detectors based on pyroelectric thin films

Intrinsic infrared detectors

Near room-temperature IR photo-detectors

The ability to grow complex multilayer structures in Hg1-xCdxTe by epitaxial techniques has made it possible to produce a range of new devices such as infrared LEDs, lasers, and two-color infrared detector arrays. The devices described here, however, are designed to operate at temperatures above 145K and include both infrared sources and detectors. Three layer ppn structures, where the underlined symbols mean wider gap, have close to Auger limited RoAs at temperatures above 145K. Under reverse bias, the devices exhibit Auger suppression leading to useful detectivities at room temperature. The diodes exhibit forward biased electroluminescence at room temperature although the efficiency of this emission is found to fall rapidly as the peak wavelength is increased toward 9 μm due to increased Auger recombination rates. By reverse biasing them, however, the devices show negative luminescence as a result of reducing the electron and hole densities below their thermal equilibrium value. The diode emitters have a higher quantum efficiency when used in this mode due to Auger suppression of the dark current.

J. Piotrowski

Papers

Uncooled photoconductive (Cd,Hg)Te detectors for the 8–14 μm region

On the performance of non-cooled CdHgTe photoelectromagnetic detectors for 10.6 μm radiation

Interference photoelectromagnetic effect in graded-gap semiconductors

Applications of group II/group VI compounds to the design of laser radiation detectors