Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure

Circulating cytokines and risk of developing hypertension: a systematic review and meta-analysis

Background: Immune responses play a significant role in hypertension, though the importance of key inflammatory mediators remains to be defined. We used a systematic literature review and meta-analysis to study the associations between key cytokines and incident hypertension. Methods: We performed a systematic search of Pubmed/Medline, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL), for peer-reviewed studies published up to August 2022. Incident hypertension was defined as systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg and/or the use of antihypertensive medications. Random effects meta-analyses were used to calculate pooled hazard ratios (HRs)/risk ratios (RRs) and 95% confidence intervals by cytokine levels (highest vs. lowest quartile). Results: Only IL-6 and IL-1β levels have evidence allowing for quantitative evaluation concerning the onset of hypertension. Six studies (10,406 participants, 2,932 incident cases) examined the association of IL-6 with incident hypertension. The highest versus lowest quartile of circulating IL-6 was associated with a significant HR/RR of hypertension (1.61, 95% CI: 1.00 to 2.60; I2=87%). After adjusting for potential confounders, including body mass index (BMI), HR/RR was no longer significant (HR/RR: 1.24; 95% CI, 0.96 to 1.61; I2= 56%). About IL-1β, neither the crude (HR/RR: 1.03; 95% CI, 0.60 to 1.76; n=2) nor multivariate analysis (HR/RR: 0.97, 95% CI, 0.60 to 1.56; n=2) suggested a significant association with the risk of developing hypertension. Conclusions: A limited number of studies suggest that higher IL-6, but not IL-1β, might be associated with the development of hypertension

Improvement of Electrical Properties of Hg1−x\text{}_{1-x}Znx\text{}_{x}Se upon Doping with Fe

Results of measurements of electron concentration and mobility in mixed crystals of Hg$\text{}_{1-x}$Zn$\text{}_{x}$Se (0 ≤ x ≤ 0.07) doped with resonant Fe donors (0 ≤ n$\text{}_{Fe}$ ≤ 5 × 10$\text{}^{19}$ cm$\text{}^{-3}$) at liquid helium temperatures are presented. The data show that there is a considerable improvement of the electrical properties of the material when Fe impurities are present. The analysis of the mobility in terms of the scattering from ionized centers (accounting for possible spatial correlation of impurity charges) and the alloy scattering is in agreement with the measured data

Peculiarities of Electron Transport in PbTe:Cr due to Presence of Resonant Impurity State

The results of transport investigation of Pb$\text{}_{1-x}$Cr$\text{}_{x}$Te (x ≤ 0.009) in temperature range 3.5-300 K are presented. The obtained electron concentration and electron mobility vs. temperature and Cr concentration data are interpreted and discussed within the model assuming that Cr in PbTe forms a donor state resonant with the conduction band

Structural and Electrical Properties of Low Concentration SnTe Layers and PbTe/SnTe Heterostructures Grown by MBE

We analyse properties of thin SnTe layers and PbTe/SnTe heterostructures grown by MBE on BaF$\text{}_{2}$(111) substrates. Reflection high energy electron diffraction patterns registered during MBE growth of the samples as well as post-growth X-ray diffraction measurements evidence a high structural perfection of 0.6 μm thick SnTe layers and (50 Å PbTe)/(50 Å SnTe) superlattices. The full width at half maximum values of (222) X-ray rocking curves measured for these thin SnTe layers crystallized in the optimal MBE growth conditions are about 300 arcsec; the carrier concentrations can be tuned from 5×10$\text{}^{19}$ cm$\text{}^{-3}$ to 10$\text{}^{2 1}$ cm$\text{}^{-3}$ depending on the MBE process parameters

Transport and Magnetic Properties of PbTe:Cr and PbSnTe:Cr

We present the results of the experimental studies of the low temperature transport and magnetic properties of PbTe, Pb$\text{}_{1-x}$Sn$\text{}_{x}$Te (x ≤ 0.3) and SnTe crystals doped with 0.5 at.% of chromium. Cr was found to be a resonant donor in PbTe and PbSnTe. Magnetic susceptibility measurements revealed that PbTe:Cr and Pb$\text{}_{1-x}$Sn$\text{}_{x}$Te:Cr (x ≤ 0.2) are Curie paramagnets whereas SnTe:Cr exhibits van Vleck paramagnetism

Electron Paramagnetic Resonance of Cr in PbTe

We present the results of the low temperature electron paramagnetic resonance (EPR) and transport investigations of the crystals of Pb$\text{}_{1-x}$Cr$\text{}_{x}$Te (x ≤ 0.01). The samples with chromium concentrations x ≥ 0.0015 are all n-type. For these samples we observe the single EPR line with the g-factor decreasing from g = 1.97 till g = 1.93 with increasing carrier concentration. This resonance can be attributed to electrically and magnetically active Cr$\text{}^{3+}$ ions. The crystals with Cr concentration x ≤ 0.0015 may be both n- and p-type. The EPR spectrum of these samples consists of two lines: the one discussed above and the other one with g = 1.99 observed only for samples with electron concentration n ≤ 10$\text{}^{18}$ cm$\text{}^{-3}$

Transport and Magnetic Properties of Pb1−x−y\text{}_{1-x-y}Sny\text{}_{y}Mnx\text{}_{x}Te (x ≤ 0.16)

Hall constant, conductivity and magnetic susceptibility of Pb$\text{}_{1-x-y}$Sn$\text{}_{y}$Mn$\text{}_{x}$Te semimagnetic semiconductor were investigated as a function of Mn content (x = 0.04, 0.09, 0.16, y = (0.7-0.8)) in the temperature range T = (4 - 300) K. A ferromagnetic phase transition takes place at T = 5 K for samples with x = 0.04, at T = 10 K for x = 0.09 and at T = 20 K for x = 0.16. For crystals with x ≥ 0.09 the strong temperature dependence of the Hall constant is observed for temperatures below 40 K. Magnetic field characteristics of the Hall effect is strongly non-linear at T = 4.2 K. No significant temperature or magnetic field dependence of conductivity is observed in the whole temperature range studied. The observed transport anomalies are due to the anomalous Hall effect

PbSe:Cr - New Resonant Donor System

Hall effect, conductivity, electron paramagnetic resonance and magnetization of Pb$\text{}_{1-x}$Cr$\text{}_{x}$Se (x ≤ 0.01) crystals were measured as a function of Cr content and electron concentration. The experimental results suggest that Cr in PbSe creates a resonant donor state with the energy of about 125 meV above the bottom of the conduction band

Magnetotransport Study of MBE grown Pb1−x\text{}_{1-x}Eux\text{}_{x}Se Epilayers

Hall effect and electron conductivity investigations of MBE grown epilayers of Pb$\text{}_{1-x}$Eu$\text{}_{x}$Se (0 ≤ x ≤ 0.06) as a function of temperature and magnetic field are reported. The strong Hall coefficient dependence on the magnetic field was found for p-type samples grown with Se excess. The possible origins of this effect are discussed