We present here the magnetotransport experiment performed with a magnetic field up to 30 T on a 10 nm-wide p-type PbTe quantum well. Pronounced Shubnikov-de Haas oscillations and the integer quantum Hall effect are clearly observed, demonstrating the transport of a confined two-dimensional hole gas with negligible parallel conduction at low temperatures. The sequence of filling factors can be explained by considering the magnetic field evolution of Landau levels derived from two longitudinal and one oblique occupied subbands and taking Zeeman spin splitting into account. During illumination, the total carrier density of the system is raised by 15%, which leads to a plateau sequence in the integer quantum Hall effect with higher filling factors in comparison to the dark condition.

In this work, we have investigated the heat sensitivity of a Zn1-xCdxO (x= 0.03-1) films obtained by spraypyrolysis under the influence of atmospheric air, considering the substrate type, air temperature, and Cd concentration. We found a transition in the electrical conductivity behavior when x is around 0.55 (55 at.% Cd). This transition is related to the structural phase transition that also occurs close to this concentration. It has been proved that the thermal response amplitude is directly related to the surface morphology of films, which depends on the substrate type and the Cd concentration. We found that thermal sensitivity and signal quality are higher for samples grown on top of Si substrates. The conductivity changes are reproducible over a strategic temperature range (50-100 degrees C), making the films available for practical applications.

This work presents the results of magnetotransport measurements performed on a 156 nm-thick Bi2Te3 epitaxial film in the temperature range of 1.9–300 K, showing Shubnikov–de Haas oscillations for temperatures below 50 K. A detailed analysis of oscillations as a function of temperature provides the main transport parameters, including the Landé g-factor and cyclotronic masses. A systematic analysis of fast Fourier transform, performed on the oscillations, indicates that the origin of the oscillation pattern is not related to the topological surface states but from the Rashba splitting of the Bi2Te3 Fermi surface.

In this work, we present the results of photoconductivity measurements performed in the temperature range of 12 K–300 K on a 150 nm-thick Bi2Te3 film grown by molecular beam epitaxy on a (111) BaF2 substrate. A transition from negative to positive photoconductivity is found to occur around 125 K. Resistivity and Hall data measured under light and dark conditions qualitatively elucidate the observed phenomena. The Arrhenius plot of recombination times obtained from photoconductivity decay curves measured at different temperatures gives the activation energy associated with the bulk trap level. Using this activation energy as the effective trap potential, we calculated the generation and recombination rates as a function of temperature. The analysis provides a quantitative explanation that predicts the transition effect observed in the experiment. No evidence of contribution from surface states is found from the magnetoresistance curves measured at low temperatures.

In this work, bismuth telluride films are grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates, using stoichiometric Bi2Te3 and additional Te solid sources. The growth dynamics and structural defects are investigated in detail as function of substrate temperature, Bi2Te3 flux and extra Te supply, by means of atomic force microscopy, Raman spectroscopy and reciprocal space mapping. The growth rate increases linearly with the Bi2Te3 flux and the most appropriate conditions to grow high-quality Bi2Te3 single layers is found to be in a narrow window of MBE parameters. At low growth temperatures Te clusters are formed, while the Te deficit increases with raising substrate temperature and decreasing deposition rate. It results in films with Bi-richer phases due to the formation of Bi double layers in between Bi2Te3 quintuple layers. The electronic transport properties are also studied by temperature dependent resistivity and Hall measurements. By properly changing the substrate temperature and/or the extra Te supply, the behavior of the films can vary from insulating to metallic as well as the major carriers from p- to n-type. The electronic phase diagram presented here provides a fast route to control the bulk conductance properties of bismuth telluride, which enables the production of intrinsic bulk insulating films. In addition, the results suggest the possibility of growing intrinsic sharp p-n junctions of Bi2Te3 by properly monitoring the occurrence of structural defects, which is the first step for practical applications of this topological insulator material.

We investigated the photoconductivity effect in n-type PbTe/Pb0.88Eu0.12Te quantum wells for a temperature range of 300–10 K using infrared light. The measurements revealed that at high temperatures, the photoresponse has small amplitude. As temperature decreases to T ∼ 75 K, however, the photoconductivity amplitude increases reaching a maximum value 10 times higher than the original value before illumination. From Hall measurements performed under dark and light conditions, we show that this effect is a result of the carrier concentration increase under illumination. Unexpectedly, for further reduction of temperature, the amplitude starts to decrease again. The electrical resistance profiles indicate that the transport occurs through barriers and the well that behave as two parallel channels. For temperatures below 75 K, transport is more effective in the quantum well, where the signal reduction can be associated with the electron-electron scattering due to the increase in the carrier concentration that occurs under illumination. We also used the random potential model to explain the origin of the persistent effect observed in the photoconductivity curves.

We investigated the photoconductivity effect in p-type Pb1-xEuxTe films for x = 0.01, 0.02, 0.03, 0.05, and 0.06 at T = 300 K. The measurements revealed a clear transition from negative to positive photoconductivity as the Eu content x is increased at room temperature. This transition is related to the metal-insulator transition that occurs due to the disorder originated from the introduction of Eu atoms and it is an Anderson transition. Our investigation found that, from the potential application point of view, the sample x = 0.06 is more suitable, i.e., it presents an almost noise-free signal and the higher photoconductivity amplitude response. The photoconductive amplitude response for the sample with x = 0.06 was investigated further in the temperature range of 77-300 K and, surprisingly, multiple additional transitions were observed with amplitudes that reached around 200 times the original value before illumination. We show that this anomalous behavior is a consequence of the generation and recombination rates between the bands and the 4f level and a defect level located inside the band gap.