A. N. Akimov

Injection currents in narrow-gap (Pb1−xSnxTe):In insulators

The low-temperature current-voltage characteristics of narrow-gap (Pb1−xSnxTe):In have been studied experimentally and calculated for a wide range of electric fields. It is shown that the obtained data are satisfactorily described in terms of a space-charge-limited current model in the presence of traps. The concentration and energy depth of the traps have been estimated.

Photosensitivity of Pb1−x SnxTe:In films in the terahertz region of the spectrum

An increase in the electrical conductivity is observed in the Pb1−xSnxTe:In/BaF2 films subjected to laser radiation with a wavelength λ=336.8 μm (the frequency of ∼0.9×1012 Hz) at the liquid-helium temperature; this increase cannot be accounted for by a heating of the sample. The observed photosignal-relaxation time does not exceed the RC time constant of the measurement circuit (this time constant amounts to fractions of seconds) and is much shorter than in the case of illumination within the fundamental absorption band of Pb1 − xSnxTe:In. The results obtained relate to an increase in the low-frequency permittivity ɛ as a result of excitation (by photons of the submillimeter region) of one or two transverse optical phonons in the center vicinity of the Brillouin zone at the branch responsible for the ferroelectric phase transition. This circumstance brings about an increase in the space-charge-limited injection current that flows from the contacts without a generation of free charge carriers in the bulk.

Industrial prospects of Pb1 − xSnxTe:In with x > 0.3 solid solutions for photodetectors with extended sensitivity spectral range

Photoelectric properties of Pb1 − xSnxTe:In films with composition x > 0.3 in the temperature range from 4.2 to 80 K have been investigated. High sample sensitivity to black-body radiation has been discovered at the temperature of helium, and as the temperature of the radiation source decreases the sensitivity increases, which can be connected with the optical-frequency transition in the short-wavelength infrared and terahertz spectral range. The detectivity value D* = 8.2 × 1016 cm · Hz1/2/W corresponding to the NEP = 3.1 × 10−18 W/Hz1/2, has been obtained at detector temperature 4.2 K and TBBR = 15 K.

Terahertz detectors based on Pb1−xSnxTe:In films

Results of experimental studies of Pb1−xSnxTe:In films grown by molecular beam epitaxy with the tin concentration close to band inversion are presented. An optimal concentration of indium is determined, and films with x > 0.3 are obtained, where the so-called metal-insulator transition is observed. Photoconductor prototypes are fabricated, and the photocurrent induced by free electron laser radiation in the range of 140–205 µm is measured. A possibility of using photoconductors for recording the own radiation of a body heated to a temperature of 300 K in a passive mode, including systems of image registration in the terahertz spectral range, is estimated.

Specific temperature-related features of photoconductivity relaxation in PbSnTe:In films under interband excitation

The time dependences of variations in the photoconductivity of PbSnTe:In films in the range of T ≈ 19—25 K upon interband excitation are studied. It is found that the character of conductivity relaxation after switch-off of illumination depends on the duration and intensity of the preceding illumination. In this case, the characteristic times of relaxation for various modes of illumination can differ by more than an order of magnitude. The obtained results are discussed in the context of a model assuming the presence of a quasicontinuous spectrum of capture levels in the band gap of PbSnTe:In and also a possible effect on the parameters of these levels of the ferroelectric phase transition, the temperature of which is found to be in the temperature range under study

Submillimeter matrix photosensitive device on PbSnTe : In films

Principles of operation of large-scale photodetector arrays for image visualization in a submillimeter spectral range are considered. Parameters of a thermal picture produced on an intermediate screen by a submillimeter component of radiation of an object with a temperature of about 300 K are estimated. Photodetector array parameters required for registration of the intermediate screen radiation are analyzed. The possibility of creating large-scale photodetector arrays on PbSnTe : In films for imaging objects with a room temperature without additional submillimeter illumination is shown.

Effect of the material of injecting contacts on the CVCs of Pb1 − xSnxTe:In films

The flowing of the injection current in Pb1 − xSnxTe:In structures (x ≥ 0.3) with various metal contacts at the temperature of helium is considered. The current-voltage characteristics (CVCs) of the structures in the dark and when they are illuminated from the blackbody model are given. It is found that the CVCs depend on the materials of the metal contact. The localized state density distribution over the forbidden band in structures with various contacts is given and the influence of the contact region and localized states on the CVC is discussed. The problems of constructing photodetectors with optimum threshold characteristics are discussed.

Giant negative photoconductivity of PbSnTe:In films with wavelength cutoff near 30 μm

Experimental results on the photoconductivity dynamics in PbSnTe:In films with a high SnTe content and corresponding fundamental absorption edge near 30 μm at liquid helium temperatures are reported. The possible causes for the giant (over two orders of magnitude) negative photoconductivity of the samples are discussed.

Effect of the surface on transport phenomena in PbSnTe:In/BaF2 films

The effect of the surface on the I–V characteristics of PbSnTe:In film-based structures is investigated in zero magnetic field and in a magnetic field of B ≤ 4 T with different orientations, including in the mode of current limited by space charge. Analysis of the features in the experimental data obtained at different magnetic-field directions and upon layer-by-layer etching of the films shows that the contributions of the free film surface and interface with the substrate to transport phenomena are significantly different and can be caused by a difference in the parameters of localization centers near these surfaces.

Long-wavelength sensitivity limit in MBE-grown PbSnTe:In films: Correlation with the film structure and composition

PbSnTe:In films with a long-wavelength sensitivity limit of over 20 μm and low “dark” conductivity are studied. The spectral dependences of the photoconductivity obtained at different temperatures using a Fourier spectrometer are compared with data on the film composition determined by X-ray microanalysis. The established nonmonotonic temperature dependence of the long-wavelength sensitivity limit is attributed to the combination of the temperature dependence of the PbSnTe band gap and the Burstein–Moss effect making the largest contribution to low-temperature measurements due to the long lifetime of excess charge carriers. It is shown that the difference between the band-gap values determined from the measured composition and temperature dependences of the long-wavelength sensitivity limit can be related to the inhomogeneity of the composition of the films grown by molecular beam epitaxy.