Quantum Oscillations of Photocurrents in HgTe Quantum Wells with Dirac and Parabolic Dispersions

We report on the observation of magneto-oscillations of terahertz radiation induced photocurrent in HgTe/HgCdTe quantum wells (QWs) of different widths, which are characterized by a Dirac-like, inverted and normal parabolic band structure. The photocurrent data are accompanied by measurements of photoresistance (photoconductivity), radiation transmission, as well as magneto-transport. We develop a microscopic model of a cyclotron-resonance assisted photogalvanic effect, which describes main experimental findings. We demonstrate that the quantum oscillations of the photocurrent are caused by the crossing of Fermi level by Landau levels resulting in the oscillations of spin polarization and electron mobilities in spin subbands. Theory explains a photocurrent direction reversal with the variation of magnetic field observed in experiment. We describe the photoconductivity oscillations related with the thermal suppression of the Shubnikov-de Haas effect.Comment: 16 pages, 13 figure

Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D Topological Insulator Based on a Strained High Mobility HgTe Film

We report on the observation of cyclotron resonance induced photocurrents, excited by continuous wave terahertz radiation, in a 3D topological insulator (TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent formation is supported by complimentary measurements of magneto-transport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements respectively utilise the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods our device is an easy to handle all-electric approach, which we demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.Comment: 7 pages, 5 figure

Impact ionization induced by terahertz radiation in HgTe quantum wells of critical thickness

We report on the observation of terahertz (THz) radiation induced band-to-band impact ionization in \HgTe quantum well (QW) structures of critical thickness, which are characterized by a nearly linear energy dispersion. The THz electric field drives the carriers initializing electron-hole pair generation. The carrier multiplication is observed for photon energies less than the energy gap under the condition that the product of the radiation angular frequency $\omega$ and momentum relaxation time $\tau_{\text l}$ larger than unity. In this case, the charge carriers acquire high energies solely because of collisions in the presence of a high-frequency electric field. The developed microscopic theory shows that the probability of the light impact ionization is proportional to $\exp(-E_0^2/E^2)$, with the radiation electric field amplitude $E$ and the characteristic field parameter $E_0$. As observed in experiment, it exhibits a strong frequency dependence for $\omega \tau \gg 1$ characterized by the characteristic field $E_0$ linearly increasing with the radiation frequency $\omega$

Effect of a boron implantation on the electrical properties of epitaxial HgCdTe with different material composition

In this work the experimental results of investigations of the dynamics of accumulation and spatial distribution of electrically active radiation defects when irradiating epitaxial films of Hg1-xCdxTe (MCT) with different material composition (x). The films, grown by molecular beam epitaxy (MBE) were irradiated by B ions at room temperature in the radiation dose range 1012 -1015 ions/cm2 and with ion energy 100 keV. The results give the differences in implantation profiles, damage accumulation and electrical properties as a function of the material composition of the film

Состояние минеральной плотности кости у больных хронической обструктивной болезнью легких

Osteoporosis is one of extrapulmonary features of COPD. This study was aimed to evaluate bone mineral density (BMD) and its correlation to risk factors in patients with COPD. Forty six patients (28 postmenopausal females, 18 males, the average age, 64.3 ± 7.8 yrs) with different COPD stages participated in the study. Fifteen patients have received inhaled corticosteroids (ICS) 500 to 2000 μg of beclomethasone equivalent daily for 5 to 8 yrs. The controls were 38 non COPD patients (35 postmenopausal females, 3 males) comparable to age, smoking history, and co morbidity. BMD was measured in lumbar vertebrae and proximal parts of right and left hips using X ray dual energy absorptiometry. Osteopenia was found in 20 COPD patients (43.48 %) and osteoporosis was in 11 (23.91 %) ones. The mean T criterion in lumbar vertebrae and both femoral necks of COPD patients was significantly lower compared to controls (р = 0.0010–0.0024). BMD in lumbar vertebrae (р = 0.0005–0.006) and femoral necks (р = 0–0,007) was also lower in COPD patients. Lumbar vertebra height did not differ in COPD patients and the controls. We also analyzed sub-groups of severe (FEV1 < 50 %pred.) and mild to moderate COPD patients separately. Those with severe COPD had osteopenia and osteoporosis more often (52.6 % vs 37 % and 36.8 % vs 14.8 %, respectively) and T criterion and BMD in both sites reliably lower. These results suppose a role of hypoxia in development of osteoporosis. Both T criterion and BMD in all sites correlated with body mass index (r = 0,453–0,743, p = 0; and r = 0,425–0,663; р = 0, respectively). There was no correlation between cumulative dose of ICS and BMD. No gender differences of BMD in COPD patients indicated that the loss of BMD in COPD could be relevant to chronic pulmonary disease but not to hormonal disorders. We conclude that loss of BMD is one of the systemic effects of COPD.Одним из внелегочных проявлений ХОБЛ является остеопороз. Целью настоящего исследования явилась оценка состояния минеральной плотности кости (МПК) у больных ХОБЛ и выявление связи с различными факторами риска. В исследовании участвовали 46 больных с различными стадиями ХОБЛ, средний возраст 64,3 ± 7,8 года (28 женщин в менопаузе, 18 мужчин). 15 больных получали ингаляционные глюкокортикоиды (иГК) 500–2000 мкг/сут в пересчете на беклометазон в течение 5–8 лет. Контрольную группу составили 38 пациентов: 35 женщин в постменопаузальном периоде и 3 мужчины, сравнимых по возрасту, стажу курения, наличию и характеру сопутствующих заболеваний, но без ХОБЛ. МПК поясничного отдела позвоночника и проксимальных отделов обеих бедренных костей определяли методом рентгеновской двухэнергетической абсорбциометрии. Остеопения выявлена у 20 (43,48 %) больных, остеопороз — у 11 (23,91 %) больных ХОБЛ. Среднее значение Т критерия в поясничных позвонках и шейках правой и левой бедренных костей у больных ХОБЛ было достоверно ниже, чем в группе контроля (р = 0,0010 — 0,0024). МПК поясничных позвонков (р = 0,0005 — 0,006) и шеек обеих бедренных костей (р = 0—0,007) была ниже у больных ХОБЛ по сравнению с контрольной группой. Высота поясничных позвонков у больных ХОБЛ и в контрольной группе достоверно не отличалась. При выделении группы больных тяжелой ХОБЛ (ОФВ1 , %долж. < 50) получено, что у них остеопения и остеопороз встречались чаще (52,6 % против 37 % и 36,8 % против 14,8 % соответственно), показатели Т критерия и МПК в поясничных позвонках и шейке бедренной кости были достоверно ниже, чем при легкой и среднетяжелой ХОБЛ. Это позволяет предположить роль гипоксии в развитии остеопороза. Показана корреляция между индексом массы тела (ИМТ) и показателями Т критерия в поясничных позвонках и шейке бедренной кости (r = 0,453–0,743, р = 0), МПК поясничных позвонков и шейки бедренной кости и ИМТ (r = 0,425–0,663; p = 0). Не выявлена связь между кумулятивной дозой ИГК и показателями МПК. Отсутствие половых различий в показателях МПК свидетельствует, что потеря МПК у больных ХОБЛ связана именно с хронической легочной патологией, а не с дисгормональными нарушениями. Таким образом, потеря МПК является одним из системных проявлений ХОБЛ

AlGaAs/GaAs Quantum Well Infrared Photodetectors

In this article, we present an overview of a focal plane array (FPA) with 640 × 512 pixels based on the AlGaAs quantum well infrared photodetector (QWIP). The physical principles of the QWIP operation and their parameters for the spectral range of 8–10 μm have been discussed. The technology of the manufacturing FPA based on the QWIP structures with the pixels 384 × 288 and 640 × 512 has been demonstrated. The parameters of the manufactured 640 × 512 FPA with a step of 20 μm have been given. At the operating temperature of 72 K, the temperature resolution of QWIP focal plane arrays is less than 35 mK. The number of defective elements in the matrix does not exceed 0.5%. The stability and uniformity of the FPA have been demonstrated

Венозный тромбоэмболизм как первая манифестация распространенного опухолевого процесса (синдром Труссо)

A description is given of a patient with a latent tumor process that has developed recurrent thrombosis of the superficial and deep veins of the lower extremities, common iliac veins, PE, a blood clot in the right ventricle, and a spleen infarction. The examination revealed bronchogenic lung cancer with metastases to the bronchopulmonary lymph nodes and liver, confirmed by an autopsy.Приводится описание больного со скрыто протекающим опухолевым процессом, у которого развились рецидивирующие тромбозы поверхностных и глубоких вен нижних конечностей, общих подвздошных вен, тромбоýмболия легочной артерии, тромб в правом желудочке, инфаркт селезенки. При обследовании выявлен бронхогенный рак легкого с метастазами в бронхопульмональные лимфоузлы и печень, подтвержденный при патологоанатомическом исследовании

High-frequency impact ionization and nonlinearity of photocurrent induced by intense terahertz radiation in HgTe-based quantum well structures

We report on a strong nonlinear behavior of the photogalvanics and photoconductivity under excitation of HgTe quantum wells (QWs) by intense terahertz (THz) radiation. The increasing radiation intensity causes an inversion of the sign of the photocurrent and transition to its superlinear dependence on the intensity. The photoconductivity also shows a superlinear raise with the intensity. We show that the observed photoresponse nonlinearities are caused by the band-to-band light impact ionization under conditions of a photon energy less than the forbidden gap. The signature of this kind of impact ionization is that the angular radiation frequency omega = 2 pi f is much higher than the reciprocal momentum relaxation time. Thus the impact ionization takes place solely because of collisions in the presence of a high-frequency electric field. The effect has been measured on narrow HgTe/CdTe QWs of 5.7 nm width; the nonlinearity is detected for linearly and circularly polarized THz radiation with different frequencies ranging from f = 0.6 to 1.07 THz and intensities up to hundreds of kW/cm(2). We demonstrate that the probability of the impact ionization is proportional to the exponential function, exp(-E-0(2)/E-2), of the radiation electric field amplitude E and the characteristic field parameter E-0. The effect is observable in a wide temperature range from 4.2 to 90 K, with the characteristic field increasing with rising temperature