In the last decade, infrared imaging detectors trend has gone for smaller pixels and larger formats. Most of the time, this scaling is carried out at a given total sensitive area for a single focal plane array. As an example, QVGA 30 µm pitch and VGA 15 µm pitch exhibit exactly the same sensitive area. SXGA 10 µm pitch tends to be very similar, as well. This increase in format is beneficial to image resolution. However, this scaling to even smaller pixels raises questions because the pixel size becomes similar to the IR wavelength, but also to the typical transport dimensions in the absorbing material. Hence, maintaining resolution for such small pixel pitches requires a good control of the modulation transfer function and quantum efficiency of the array, while reducing the pixel size. This might not be obtained just by scaling the pixel dimensions. As an example, bulk planar structures suffer from excessive lateral diffusion length inducing pixel-to-pixel cross talk and thus degrading the modulation transfer function. Transport anisotropy in some type II superlattice structures might also be an issue for the diffusion modulation transfer function. On the other side, mesa structures might minimize cross talk by physically separating pixels, but also tend to degrade the quantum efficiency due to a non-negligible pixel fill factor shrinking down the pixel size. This paper discusses those issues, taking into account different material systems and structures, in the perspective of the expected future pixel pitch infrared focal plane arrays.

Infrared thermal imaging, using cooled and uncooled detectors, is continuously gaining attention because of its wide military and civilian applications. Futuristic requirements of high temperature operation, multispectral imaging, lower cost, higher resolution (using pixels) etc. are driving continuous developments in the field. Although there are good reviews in the literature by Rogalski [1–4], Martyniuk et al. [5] and Rogalski et al. [6] on various types of infrared detectors and technologies, this paper focuses on some of the important recent trends and diverse applications in this field and discusses some important fundamentals of these detectors.