The process of formation and relaxation of charge-carrier exclusion in a structure with an h-l-junction has been studied both theoretically and experimentally. It is shown, for the first time, that temporal dependencies of the most important process characteristics, such as the exclusion length, the extent of integral charge-carrier depletion in the base, and the current establishment, may be expressed by simple analytical formulae. The modelling experiment has been carried out using Ge crystals with intrinsic conductivity (T 300 K). In order to 'visualize' the spatial distribution of the charge carriers, the transmission beyond the edge of fundamental absorption and non-equilibrium thermal emission of the structure base in the spectral range 8-12 µm have been investigated. It is shown that thermal generation of charge carriers by the ohmic contact and base surface plays a key role in the process of exclusion relaxation. The difference between process duration in the cases of establishment of a steady-state current and spatial-charge-carrier distribution is explained by the formation of a high electric field domain.
IR probing measurements of germanium samples are presented, showing, according to the theory [1], accumulation and exclusion effects due to current flow through an internal built-in electric field appearing in the inhomogeneous part of the crystal.
Thermal emission characteristics of a wide gap semiconductor structure with an h-l junction have been studied with the view of application to long wavelength (8-12 µm) IR sources. The device performs emission modulation in the spectral range below the edge of fundamental absorption via modulation of the charge carrier concentration in the structure base due to the contact exclusion effect. It is experimentally and theoretically shown that the structure base doping level determines both the magnitude of IR signal and the radiating region length. Experimental studies have been carried out with the structures based on p-Ge at temperatures from 300 to 430 K. It is shown that the maximum active region length may achieve 1 cm with emission intensity of ∼mW cm −2 and operation speed of ∼100 µs.
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