The performance of HgCdTe barrier detectors with cut-off wavelengths up to 3.6 μm fabricated using metaloorganic chemi- cal vapour deposition operated at high temperatures is presented. The detectors’ architecture consists of four layers: cap contact, wide bandgap barrier, absorber and bottom contact layer. The structures were fabricated both with n- and p-type absorbing layers. In the paper, different design of cap-barrier structural unit (n-B_p′, n⁺-B_p′, p+-B_p) were analysed in terms of various electrical and optical properties of the detectors, such as dark current, current responsivity time constant and detectivity.

The devices with a p-type cap contact exhibit very low dark current densities in the range of (2÷3)×10^-4 A/cm² at 230 K and the maximum photoresponse of about 2 A/W in wide range of reverse bias voltage. The time constant of measured de- vices with n-type cap contact and p-type absorbing drops below 1 ns with reverse bias while the detectivity is at the level of 1010 cm ^∙ Hz1/2/W.

In the last decade several papers have announced usefulness of two-dimensional materials for high operating temperature photodetectors covering long wavelength infrared spectral region. Transition metal dichalcogenide photodetectors, such as PdSe ₂/MoS ₂ and WS ₂/HfS ₂ and WS ₂/HfS ₂ heterojunctions, have been shown to achieve record detectivities at room temperature (higher than HgCdTe photodiodes). Under these circumstances, it is reasonable to consider the advantages and disadvantages of two-dimensional materials for infrared detection. This review attempts to answer the question thus posed.

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.