A prototype of a metal–insulator–semiconductor field-effect transistor based on PbSnTe:In/(111)BaF2 film with an Al2O3 gate dielectric was designed for the first time. With the gate voltage applied in the range – 7.7 V < Ugate < +7.7 V the relative modulation in the drain-source current Ids/Ids attained near five-fold change at T = 4.2 K. When illuminated with rela-tively low (~100 photon/s) fluxes, negative photoconductivity was detected accompanied with a decrease in Ids by ~104 times and a simultaneous decrease in Ids by ~103 times or even more. The estimated detectivity was about 71016 cmHz0.5W-1 at a wavelength  about 25 micron with the accumulation time about 0.5 s. A qualitative model is discussed which assumes the ex-istence of deep traps and a photo-capacitance effect.

Results on the creation and properties of transistor-type MIS structures (MIST) with an Al2O3 thin-film gate dielectric based on PbSnTe:In films obtained by molecular beam epitaxy are presented. The source-drain current-voltage characteristics (CVC) and gate characteristics of the MIST at Т = 4.2 К have been investigated. It is shown that in MIST based on PbSnTe:In films with n ~ 1017 cm-3 the modulation of the channel current reaches 7 – 8 % in the range of gate voltages – 10 V < Ugate < + 10 V. The features of the source-drain CVC and the gate characteristics for a pulsed and sawtooth variation of Ugate are considered.

The surface topology of epitaxial films of lead tin telluride solid solution (including with In additive, Pb1 – xSnxTe:In) has been examined using atomic force microscopy. The films have been grown on BaF2(111) single-crystal substrates and on a CaF2/BaF2 buffer layer covering a Si(111) wafer. It has been shown that the relief statistical parameters depend on film growth conditions and the incorporation mechanism of indium, an excess amount of which has been detected on the surface by ex situ XPS.

The topology of the surface of epitaxial films of lead tin telluride solid solution, including those with the addition of indium (Pb1-xSnxTe:In), grown on single-crystal BaF2 (111) substrates and a CaF2/BaF2 buffer layer on Si (111) was studied by atomic force microscopy. It is shown that the characteristic statistical indicators of the relief are due to the peculiarities of film growth and the mechanism of incorporation of Indians, the excess content of which was registered on the surface ex situ by X-ray photoelectron spectroscopy.

The dependence of the photoconductivity sign on the bias voltage, intensity and duration of illumination was studied in PbSnTe:In films in the space charge limited current regime. The role of traps with a complex energy spectrum, including the surface traps, in the observed effects is discussed

High-resistance Pb1 –xSnxTe〈In〉 layers grown by molecular beam epitaxy on BaF2(111) substrates with compositions close to band inversion have been investigated. The I–V characteristics and relaxation dependences of the photocurrent of the structures in dependence on the chemical surface treatment and subsequent exposure of the samples in air have been examined. It has been observed that the characteristics significantly transform depending on the physicochemical surface state. It has been found that the chemical surface treatment in the hydrochloric acid solution in isopropyl alcohol leads to an increase in the current by up to four orders of magnitude with the subsequent recovery of the I–V characteristics upon exposure of the samples in air for several days.

Рассмотрены особенности фоточувствительности структур на основе пленок узкозонного твердого раствора PbSnTe:In, полученных методом МЛЭ на подложках (111)BaF2. Исследованы образцы с содержанием SnTe ~ 24-32 %, для которых при гелиевых температурах в отсутствие освещения наблюдалось полу-изолирующее состояние [1]. Спектральная чувствительность в ИК области определяется межзонными переходами в условиях захвата одного типа неравновесных носителей заряда на локализованные состояния. Рассмотрены экспериментальные результаты по ИК чувствительности PbSnTe:In МДП-структур (диэлектрик - полипропиленовая пленка толщиной 8 мкм, величина затворного напряжения - до ±1250 В), в которых проводимость n + -i-n + канала c длиной iобласти 50 мкм определяется токами, ограниченными пространственным зарядом (ТОПЗ). Из приведенного рисунка видно, что поведение темнового и фототока качественно различно для разных полярностей затворного напряжения Uзатв. Так, в момент () для (+) наблюдалась отрицательная фотопроводимость с уменьшением тока примерно в 100 раз, тогда как для (-) фототок возрастал монотонно. Для (-) в области t > 880 с (уменьшение Uзатв) «всплеск» тока для (-) примерно в 100 раз больше по величине и существенно отличается по форме от (+). Это свидетельствует о существенном влиянии на ИК фотопроводимость локализованных состояний, расположенных на поверхности или вблизи нее, что находится в согласии с данными по влиянию химической обработки поверхности на ИК фотопроводимость [2]. Приведены экспериментальные данные по фоточувствительности структур на основе PbSnTe:In в ТГц диапазоне спектра в различных режимах. Полученные результаты анализируются на основе представлений о сложном энергетическом спектре локализованных состояний, которые могут заполняться как при освещении в фундаментальной области поглощения, так и за счет инжекции из контактов в режиме ТОПЗ.

AbstractHigh-resistance Pb_1 –_ x Sn_ x Te〈In〉 layers grown by molecular beam epitaxy on BaF_2(111) substrates with compositions close to band inversion have been investigated. The I–V characteristics and relaxation dependences of the photocurrent of the structures in dependence on the chemical surface treatment and subsequent exposure of the samples in air have been examined. It has been observed that the characteristics significantly transform depending on the physicochemical surface state. It has been found that the chemical surface treatment in the hydrochloric acid solution in isopropyl alcohol leads to an increase in the current by up to four orders of magnitude with the subsequent recovery of the I–V characteristics upon exposure of the samples in air for several days.

This paper reports a study of the current–voltage (I–V) features of the p-i-p structures based on Pb1–xSnxTe:In films with the tin content х ≈ 0.31 in which the metal–insulator transition occurs. It is shown that the photocurrent is the hole current under light interband excitation, and electron trapping is dominant. The experimental and theoretical data are compared.

Исследованы пленки PbSnTe:In с длинноволновой границей чувствительности свыше 20 мкм и низкой проводимостью без освещения. Проведено сравнение спектральных зависимостей фотопроводимости, полученных при различных температурах с использованием фурье-спектрометра, с составом пленок, определенным методом рентгеновского микроанализа. Обнаружена немонотонная зависимость длинноволнового края фоточувствительности от температуры, которая объясняется комбинацией температурной зависимости ширины запрещенной зоны PbSnTe и эффекта Бурштейна-Мосса, дающего наибольший вклад в измерения при низких температурах из-за большого времени жизни неравновесных носителей заряда. Показано, что различия в значениях ширины запрещенной зоны, определяемых из измеренного состава и температурных зависимостей длинноволнового края чувствительности, могут быть связаны с неоднородностью состава пленок, получаемых методом молекулярно-лучевой эпитаксии. DOI: 10.21883/FTP.2017.11.45114.29

The flowing of the injection current in Pb1 − x Sn x Te: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.

Results of experimental studies of Pb1−x Sn x Te: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.

Photoelectric properties of Pb1 − x Sn x Te: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 T BBR = 15 K.

Damping oscillations of a current are found in the PbSTe:In films after supplying a direct voltage to them in the absence of background illumination. A nonmonotonic transition to the steady state is discussed in the scope of the theory of the currents confined by a space charge upon the capture of electrons injected from the contacts to the traps distributed by energy, which leads to oscillating variation in polarizability and injection current. The ratio of the total current under the excitation by laser radiation with wavelength λ = 205 μm (hν = 0.006 eV) to the dark current could be larger or smaller than unity depending on the injection level of the electrons, i.e., supplied voltage, which can be interpreted in the scope of the suggested model.

В пленках PbSnTe:In после подачи на них постоянного напряжения в отсутствие фоновой засветки обнаружены затухающие колебания тока. Немонотонный переход к стационарному состоянию обсуждается в рамках теории токов, ограниченных пространственным зарядом при захвате инжектируемых из контактов электронов на распределенные по энергии ловушки, что ведет к осциллирующему изменению поляризуемости и инжекционного тока. Отношение полного тока при возбуждении лазерным излучением с длиной волны = 205 мкм (h = 0.006 эВ) к току в темноте могло быть больше либо меньше единицы в зависимости от уровня инжекции электронов, т.е. приложенного напряжения, что находит объяснение в рамках предлагаемой модели.

Under non-illumination conditions, dying oscillations of electric current in PbSnTe:In film structures were observed upon applying a constant voltage to the samples. A model for the transition of the structures to a stationary state is discussed, in which capture of electrons injected out of contacts at energy-distributed traps is assumed; this capture leads to non-monotonic variation of polarizability and injection current in PbSnTe:In.

The results of an experimental study of the kinetics of photocurrent rise in PbSnTe:In films exposed at T=4.2 K to free-electron laser radiation of wavelengths 68, 123, and 205 μm are reported. The obtained data are analyzed within the model of space-charge-limited injection currents that flow in a material with electron traps.