The electronic transport properties and optical properties of lead(II) chromate (PbCrO4) have been studied at high pressure by means of resistivity, Hall-effect, and optical-absorption measurements. Band-structure first-principle calculations have been also performed. We found that the low-pressure phase is a direct band-gap semiconductor (Eg = 2.3 eV) that shows a high resistivity. At 3.5 GPa, associated to a structural phase transition, a band-gap collapse takes place, becoming Eg = 1.8 eV. At the same pressure the resistivity suddenly decreases due to an increase of the carrier concentration. In the HP phase, PbCrO4 behaves as an n-type semiconductor, with a donor level probably associated to the formation of oxygen vacancies. At 15 GPa a second phase transition occurs to a phase with Eg = 1.2 eV. In this phase, the resistivity increases as pressure does probably due to the self-compensation of donor levels and the augmentation of the scattering of electrons with ionized impurities. In the three phases the band gap red shifts under compression. At 20 GPa, Eg reaches a value of 0.8 eV, behaving PbCrO4 as a narrow-gap semiconductor.
Electronic transport under hydrostatic pressure and peculiar properties of the impurity energy spectrum in semiconductor arsenides of n-type: InAs, CdSnAs2, CdGeAs2 and GaAs
The local environment of Ga, Se, and Tl atoms in InTe-based solid solutions was studied by EXAFS technique. It was shown that all investigated atoms are substitutional impurities, which enter the In(1), Te, and In(2) positions in the InTe structure, respectively. The electrical measurements revealed that In$_{1-x}$Ga$_x$Te and InTe$_{1-x}$Se$_x$ solid solutions become semiconductors at $x>0.24$ and $x>0.15$, respectively.
The abundance of semiconductors in our smartphones, computers, fiber optic junctions, cars, light sources, photovoltaic and thermoelectric cells results from the possibilities of controlling their properties through doping, lighting, and applying various fields. This paper, a part of the volume celebrating 100 years of the Polish Physical Society, presents a biased selection of worthwhile results obtained by researchers at the Institute of Physics, Polish Academy of Sciences relevant, as seen today, to topological matter and spintronics. Comprehensive studies, combining materials development, …
Based on the Boltzmann transport theory, we study the origin of the anomalous temperature dependence of the Nernst coefficient ($ν$) due to the phonon-drag mechanism. For narrow-gap semiconductors, we find that there are two characteristic temperatures at which a noticeable peak structure appears in $ν$. Contrarily, the Seebeck coefficient ($S$) always has only one peak. While the breakdown of the Sondheimer cancellation due to the momentum-dependence of the electron relaxation time is essential for the peak in $ν$ at low $T$, the contribution of the valence band to the phonon-drag current is …
We propose a method to realize diluted magnetic semiconductors (DMS) with p- and n-type carriers by choosing host semiconductors with a narrow band gap. By employing a combination of the density function theory and quantum Monte Carlo simulation, we demonstrate such semiconductors using Mn-doped BaZn2As2, which has a band gap of 0.2 eV. In addition, we found a new non-toxic DMS Mn-doped BaZn2Sb2, of which the Curie temperature Tc is predicted to be higher than that of Mn-doped BaZn2As2, the Tc of which was up to 230 K in the recent experiment.
An oligomeric semiconductor containing three bisthiophenediketopyrrolopyrole units (Tri-BTDPP) was synthesized and characterized. Tri-BTDPP has a HOMO level of -5.34 eV, a broad absorption close to the near infrared region and a low band gap of 1.33 eV. Additionally, a promising hole mobility of 1 x 10-3 cm V-1 s-1 was achieved after thermal annealing at 150 C in organic field effect transistors (OFET). Organic photovoltaic (OPV) cells containing Tri-BTDPP and PC71BM as the donor/acceptor couple exhibited a power conversion efficiency (PCE) of 0.72%. Through an intensive study of the active la…
The presence of defects in the narrow-gap semiconductors GaSb and InSb affects their dopability and hence applicability for a range of optoelectronic applications. Here, we report hybrid density functional theory based calculations of the properties of intrinsic point defects in the two systems, including spin orbit coupling effects, which influence strongly their band structures. With the hybrid DFT approach we adopt, we obtain excellent agreement between our calculated band dispersions, structural, elastic and vibrational properties and available measurements. We compute point defect formati…
High pressure Raman spectroscopy of bulk 2H-MoTe$_2$ upto $\sim$ 29 GPa is shown to reveal two phase transitions (at $\sim$ 6 and 16.5 GPa), which are analyzed using first-principles density functional theoretical calculations. The transition at 6 GPa is marked by changes in the pressure coefficients of A$_{1g}$ and E$^{1}_{2g}$ Raman mode frequencies as well as in their relative intensity. Our calculations show that this is an isostructural semiconductor to a semimetal transition. The transition at $\sim$ 16.5 GPa is identified with the changes in linewidths of the Raman modes as well as in t…
Density functional theory based study of the pressure dependent physical properties of binary SnS compound has been carried out. The computed elastic constants reveal that SnS is mechanically stable and brittle under ambient conditions. With increasing pressure, the compound becomes ductile. The Poisson's ratio also indicates brittle-ductile transition with increasing pressure. The hardness of SnS increases significantly with pressure. The compound possesses elastic anisotropy. The ground state electronic band structure is semiconducting with a small band gap which becomes metallic under press…
We performed X-ray diffraction and electrical resistivity measurement up to pressures of 5 GPa and the first-principles calculations utilizing experimental structural parameters to investigate the pressure-induced topological phase transition in BiTeBr having a noncentrosymmetric layered structure (space group P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of lattice constants, c/a, has a minimum at pressures of 2.5 - 3 GPa. In the same range, the temperature dependence of resistivity changes from metallic to semiconducting at 3 GPa and has a plateau region betwee…
Using time-dependent density-functional theory, we investigate the electronic stopping power of self-irradiated silicon through non-adiabatic dynamics simulations. For specific velocities above 0.6 atom units, electronic stopping shows a generally assumed metallic behavior that is velocity-scaling. While in the lower velocity regime, the slope of electronic stopping power versus velocity changes and the overall magnitude are significantly greater than expectations, leading to a complete vanish of hard threshold. An analysis of the electron localization function allows us to arrive at the follo…
The generic 1-bond:2-mode percolation type Raman signal inherent to the short bond of common (A,B)C semiconductor mixed crystals with zincblende (cubic) structure is exploited as a sensitive mesoscope to explore how various ZnSe-based systems engage their pressure-induced structural transition (to rock-salt) at the sub-macroscopic scale with a focus on ZnCdSe. The Raman doublet, that distinguishes between the AC- and BC-like environments of the short bond, is reactive to pressure: either it closes (ZnBeSe, ZnSeS) or it opens (ZnCdSe), depending on the hardening rates of the two environments un…
Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of 2D layered semiconductors. We have succeeded in growing bulk single crystals of these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs were obtained, and could be exfoliated into 2D flakes. Small and brittle crystals of SiP were yielded by this method. High-pressure sintered polycrystalline SiP and GeAs have also been successfully used as a precursor in the Chemical Vapor Transport growth of these crystals in the prese…
Weyl semimetal phase in solid-solution narrow-gap semiconductors
本文从理论上研究了具有强自旋-轨道相互作用的磁掺杂固溶体窄隙半导体如Cr掺杂Bi $_2$（Se $_x$ Te $_{1-x}$）$_3$中的铁磁有序。我们计算了杂质和巡游电子的自发磁化强度，并估计了临界温度作为磁性掺杂剂浓度和自旋轨道相互作用强度的函数。发现临界温度与掺杂浓度成正比，且随自旋轨道相互作用的增强而提高。铁磁相变可以使系统转变为具有动量空间中分离的一对外尔点的外尔半金属。
Two-dimensional materials have significant potential for the development of new devices. Here we report the electronic and structural properties of $β$-GeSe, a previously unreported polymorph of GeSe, with a unique crystal structure that displays strong two-dimensional structural features. $β$-GeSe is made at high pressure and temperature and is stable under ambient conditions. We compare it to its structural and electronic relatives $α$-GeSe and black phosphorus. The $β$ form of GeSe displays a boat conformation for its Ge-Se six-ring, while the previously known $α$ form, and black phosphorus…
Engineering a Correlated Narrow-Gap Semiconductor: Effects of Ga Substitution in EuZn$_2$P$_2$
Universidade Federal do ABC (UFABC)（圣安德雷联邦大学）；Instituto de Física, Universidade de São Paulo (USP)（圣保罗大学物理研究所）；Centro Brasileiro de Pesquisas Físicas（巴西物理研究中心）；Departamento de Física, Universidad del Valle（瓦尔列大学物理系）
2D ferroelectric narrow-bandgap semiconductor Wurtzite' type alpha-In2Se3 and its silicon-compatible growth
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences（中国科学院金属研究所沈阳材料科学国家实验室）；School of Materials Science and Engineering, University of Science and Technology of China（中国科学技术大学材料科学与工程学院）；School of Physical Science and Technology, Jiangsu Key Laboratory of Frontier Material Physics and Devices, Soochow University（苏州大学江苏省前沿材料物理与器件重点实验室物理科学与技术学院）；Collaborative Innovation Center of Extreme Optics, Shanxi University（山西大学极端光学协同创新中心）；Center for Quantum Matter, School of Physics, Zhejiang University（浙江大学物理学院量子物质研究中心）；Department of Mechanical Engineering, The University of Hong Kong（香港大学机械工程系）
Here, we demonstrate an approach that provides a precise control of the dimension of InAs from one-dimensional nanowires to wafer-scale free-standing two-dimensional nanosheets, which have a high degree of crystallinity and outstanding electrical and optical properties, using molecular-beam epitaxy by controlling catalyst alloy segregation. In our approach, two-dimensional InAs nanosheets can be obtained directly from one-dimensional InAs nanowires by silver-indium alloy segregation, which is much easier than all previously reported method, such as traditional buffering technique and select ar…
Here we present a study of magnetism in \CTO\ anatase films grown by pulsed laser deposition under a variety of oxygen partial pressures and deposition rates. Energy-dispersive spectrometry and transition electron microscopy analyses indicate that a high deposition rate leads to a homogeneous microstructure, while very low rate or postannealing results in cobalt clustering. Depth resolved low-energy muon spin rotation experiments show that films grown at a low oxygen partial pressure ($\approx 10^{-6}$ torr) with a uniform structure are fully magnetic, indicating intrinsic ferromagnetism. Firs…
Chemical pressure is an effective method to tune physical properties, particularly for diluted magnetic semiconductors (DMS) of which ferromagnetic ordering is mediated by charge carriers. Via substitution of smaller Ca for larger Sr, we introduce chemical pressure on (Sr,Na)(Cd,Mn)2As2 to fabricate a new DMS material (Ca,Na)(Cd,Mn)2As2. Carriers and spins are introduced by substitutions of (Ca,Na) and (Cd,Mn) respectively. The unit cell volume reduces by 6.2% after complete substitution of Ca for Sr, suggesting a subsistent chemical pressure. Importantly the local geometry of [Cd/MnAs4] tetra…
We review many-body effects, their microscopic origin, as well as their impact onto thermoelectricity in correlated narrow-gap semiconductors. Members of this class---such as FeSi and FeSb$_2$---display an unusual temperature dependence in various observables: insulating with large thermopowers at low temperatures, they turn bad metals at temperatures much smaller than the size of their gaps. This insulator-to-metal crossover is accompanied by spectral weight-transfers over large energies in the optical conductivity and by a gradual transition from activated to Curie-Weiss-like behaviour in th…
A pressure-induced phase transition, associated with an increase of the coordination number of In and Ta, is detected beyond 13 GPa in InTaO4 by combining synchrotron x-ray diffraction and Raman measurements in a diamond anvil cell with ab-initio calculations. High-pressure optical-absorption measurements were also carried out. The high-pressure phase has a monoclinic structure which shares the same space group with the low-pressure phase (P2/c). The structure of the high-pressure phase can be considered as a slight distortion of an orthorhombic structure described by space group Pcna. The pha…
Intercalation offers a promising way to alter the physical properties of two-dimensional (2D) layered materials. Here we investigate the electronic and vibrational properties of 2D layered MoSe$_2$ intercalated with atomic manganese at ambient and high pressure up to 7 GPa by Raman scattering and electronic structure calculations. The behavior of optical phonons is studied experimentally with a diamond anvil cell and computationally through density functional theory calculations. Experiment and theory show excellent agreement in optical phonon behavior. The previously Raman inactive A$_{2u}$ m…
