Humeniuk-Sychevska Z. Optoelectronic properties of low-dimensional structures based on narrow-gap semiconductors in the IR and THz spectral ranges

The thesis is devoted to solving the problem of developing physical principles and theoretical foundations for creating and optimizing the characteristics of the infrared (IR) and terahertz (THz)/sub-THz detectors, in particular, to the establishment of the features of the mechanisms of current formation in low-dimensional heterostructures and nanostructures based on narrow-gap semiconductors under the influence of external radiation. A model of dark current transport is developed for IR photodiodes based on p-n junctions in HgCdTe and PbTeS/PbSnTe heterojunctions. The model is based on balance equations taking into account spatially inhomogeneous trap filling, all basic charge transfer mechanisms and realistic band structure. The real parameters of IR photodiodes are extracted from their experimental current-voltage characteristics and the main factors limiting the operational characteristics of multi-element IR FPA are determined. The effects of certain technology features and damaging factors on such systems are investigated. The transport properties and noise in the HgCdTe semimetallic phase quantum well are modeled in order to study the possibility of creating a highly sensitive high-speed moderately cooled THz detector, to establish optimal parameters for achieving high electron mobility, and to develop recommendations for such optimization. The influence of finite size substrate parameters on the absorption characteristics of the THz detector-antenna systems, including multi-element detectors, is analyzed. It is shown that the substrate thickness is the key parameter that determines the behaviour of the entire system. The simulation showed that the detector array is able to work as an FPA with a uniform sensitivity of the elements for thin substrates (h <60 μm for the Si substrate) and/or at low values of the substrate dielectric constant (ε <5). Five different new low-dimensional plasmon detectors were designed, manufactured and studied: three linear FPA based on two-colour (IR/THz) hot-electron bolometers (realized on the epitaxial layers of HgCdTe) with different antenna configurations, HgCdTe quantum well field effect transistor (FET), and- double-gate FET on bilayer graphene encapsulated in hexagonal boron nitrate (hBN). Studies of the THz/sub-THz responses of these structures showed that their sensitivity and noise equivalent power (NEP) are suitable for active detection at nitrogen and room temperature.