Physica Status Solidi B: Basic Solid State Physics

Zhang, Dong; Bai, Jing; Liu, Jiaan; Zhou, Xiaoming

doi: 10.1002/pssb.202300288pmid: N/A

Flower‐like spherical micrometer‐sized particles of FeS2 and NiS2 are synthesized using the solvothermal method. The microstructure, phase composition, saturation magnetization and optical characteristics of the synthesized FeS2 and NiS2 are described, and the atomic structure, electronic structure, and optical characteristics of the materials are calculated systematically founded upon the first principles of density functional theory. This work shows that the magnetic saturation intensity of FeS2 and NiS2 is respectively 0.36 and 0.02 emu g−1. The FeS2 and NiS2 bandgaps are separately 0.81 and 2.07 eV, calculated by Tauc's relation. Through the comparison of optical properties, the maximum absorption coefficient of FeS2 and NiS2 is separately 3.26 × 105 and 3.3 × 105 cm−1, and the two crystals’ absorption coefficient accordingly drops to 0 at 23.8 and 25.8 eV, indicating that the maximum absorption value and energy absorption range of NiS2 are higher than those of FeS2. The reflectivity above 60% ranges from 15.3 to 20.6 eV and 15.2 to 21.5 eV for FeS2 and NiS2, respectively, which indicates that the reflectivity of NiS2 is stronger than that of FeS2.

Hrytsak, Andriy; Rudko, Mykola; Kapustianyk, Volodymyr; Hrytsak, Lilya; Mykhaylyk, Vitaliy

doi: 10.1002/pssb.202300289pmid: N/A

X‐ray luminescence spectra, thermally stimulated luminescence, and thermally stimulated conductivity of undoped cesium iodide (CsI) crystal are investigated in order to reach better understanding of the factors which govern the emission processes in this material. X‐ray luminescence spectra are recorded in the temperature range from 15 to 293 K. The low energy band at 2.2 eV emerging at heating above 120 K is assigned to the emission of residual impurities. Other two bands peaking at 3.6 and 4.3 eV at 15 K are attributed to the intrinsic emission of CsI due to the self‐trapped excitons (STEs). The parameters of the peaks observed in the thermally stimulated luminescence and conductivity of CsI crystal are calculated. Investigations of the thermally stimulated processes in CsI lead to the conclusion that the increase of luminescence of 4.3 eV observed above 70 K is due to release of trapped electrons, which subsequently interact with Vk centers and form on‐center STEs. The considerable ionic conductivity observed above 250 K can be explained by the influence of uncontrolled impurities of divalent metal atoms as well as Na+ ions.

Luo, Kailiang; Xu, Yang; Li, Zhengyi; Hu, Changyi; Wei, Yan

doi: 10.1002/pssb.202300269pmid: N/A

Herein, the high‐pressure impacts on the electronic, mechanical, and thermodynamic properties of MAX‐phase M2GaC (M = Nb and Ta) are calculated through the first principles. The phonon dispersion results indicate that M2GaC (M = Nb and Ta) is dynamically stable. The elastic constants and elastic modulus of Nb2GaC and Ta2GaC increase with the pressure increase, while the elastic anisotropic 3D surface structure and projection diagram show that bulk modulus, shear modulus, and Young's modulus all show anisotropy. M2GaC (M = Nb and Ta) has metallic, covalent, and ionic bonds. In addition, based on the quasiharmonic Debye model, the effects of high pressure (0–50 GPa) and temperature (0–2000 K) on the thermodynamic properties of Nb2GaC and Ta2GaC are systematically studied. The constant pressure heat capacity (CP) and thermal expansion coefficient (α) of Nb2GaC and Ta2GaC decrease with the increase of pressure, while the internal energy (U) and Gibbs free energy (G) of Nb2GaC and Ta2GaC increase with the increase of pressure. The sound velocity and kmin increase with the pressure increase, and Nb2GaC has a higher thermal conductivity than Ta2GaC.

Datta, Swarnab; Bhakti, Bhaskar; Ghosh, Manas

doi: 10.1002/pssb.202300281pmid: N/A

The present study thoroughly explores the time‐average population transfer rate (TAPTR) of impurity‐doped GaAs quantum dot (QD) pursuing the change in the spatial impurity spread (SIS). The said excitation rate is studied under the influence of Gaussian white noise (GWN). The rise of the ground‐state electronic density takes place due to different types of time‐changing fluctuations, viz. simple sinusoidal field, time‐dependent confinement potential, and time‐dependent magnetic field. GWN couples with the QD by additive and multiplicative modes. In this work, the joint influence of SIS and GWN and its pathway of inclusion and the nature of the time‐dependent perturbations are examined on the attributes of the TAPTR. The TAPTR curves are composed of steadfast rise, steadfast diminish, maximization (relevant to generation of large nonlinear optical properties), minimization, and saturation (suggesting dynamic freezing). The findings elucidate the means of fine‐tuning the TAPTR among the doped GaAs QD eigenstates in presence of noise, when the SIS undergoes a gradual change.

Lomova, Natalya V.; Chausov, Feodor F.; Dobysheva, Lyudmila V.; Ul'yanov, Aleksandr I.; Zverev, Nikolay N.

doi: 10.1002/pssb.202300278pmid: N/A

The magnetic susceptibility is measured for two series of linear organic–inorganic coordination polymers I‐Ln and II‐Ln (Ln = La–Tb). The structure of the polymers (isostructural in each series I‐Ln and II‐Ln) differs in the length and structure of the bridges and in the nearest environment of the lanthanides. The effective magnetic moments of lanthanide atoms are determined from the magnetic susceptibility. The measured magnetic moments agree with the values characteristic of isolated trivalent 3+ ions for all cases, except for Tb which demonstrates a higher value of 12.25 μB in one of the complexes. An analysis of the X‐ray photoelectron spectrum of Tb 5s makes it possible to estimate the spin magnetic moment of the Tb ion.

Bo, Rui; Tang, Yi; Li, Can; Zhang, Zhengzhong; Liu, Hao

doi: 10.1002/pssb.202300266pmid: N/A

Spin‐dependent electron transport is theoretically studied for a system with an interacting quantum dot sandwiched between a pair of ferromagnetic electrodes. By separately applying an electrical bias or a temperature gradient across the junction, a spin‐polarized current can be obtained and controlled by tuning the gate voltage. Interestingly, regardless of whether the electron transport is driven by the bias voltage or temperature difference, the current in the device always exhibits negative magnetoresistance under the control of the gate voltage. Such magnetoresistance anomalies in the current profile originate from the spin‐selective tunneling channels in quantum dots, which have been proven experimentally feasible. This device scheme is compatible with current technologies and has potential applications in spintronics or spin caloritronics.

Dhiman, Veerpal Kaur; Tripathi, Surya Kant; Prakash, Satya

doi: 10.1002/pssb.202300200pmid: N/A

The density functional theory with generalized gradient approximation is used to investigate the structural, electronic, and optical properties of Cu0.125As2S3 and Cu0.25As2S3 configurations with copper impurity at c‐face center interstitial site. The AsS bond lengths remain nearly the same but CuS bond lengths decrease with the increase in copper concentration. Both the configurations show n‐type conductivity and strong p–d hybridization in valence and conduction bands. The density of copper d states in the valence band increases with the increase in Cu content. The calculated optical constants are strongly anisotropic up to 10 eV; however, at higher energies the anisotropy diminishes. The broad peaks in the optical constants along E→$\overset{\rightarrow}{E}$||b→$\overset{\rightarrow}{b}$ and c→$\overset{\rightarrow}{c}$ axes are found in the vicinity of 2 eV. However, the peak heights increase and shift toward lower energy with the increase in copper content. Further, the static dielectric constant, refractive index, and reflectivity increase and the optical bandgap decreases with the increase in copper concentration. The comparison of optical constants shows that Cu0.25As2S3 may be as good choice as Ag0.25As2S3 for optical applications.

Zhang, Han; Chan, Kah-Yoong; Ng, Zi-Neng

doi: 10.1002/pssb.202300270pmid: N/A

Recently, researchers have shown a strong interest in research on quaternary semiconductor copper zinc tin sulfide (CZTS) photovoltaic cells. These cells have a high absorption coefficient, a direct bandgap, and excellent electrical properties. However, the toxicity of cadmium (Cd) in the cadmium sulfide (CdS) buffer layer in standard CZTS solar cells, can generate severe environmental contamination that is hazardous to humans. As a result, building a Cd‐free CZTS solar cell is critical. Meanwhile, given that the peak power conversion efficiency of CZTS solar cells stands at a modest 11%, this study is dedicated to identifying an optimal approach for replacing the environmentally hazardous CdS layers to enhance overall efficiency. SCAPS‐1D is a one‐dimensional solar cell simulation program commonly used to examine proposed solar cells without building them. This study highlights the performance of CZTS with various nontoxic buffer layers, as well as the key results obtained through numerical research with SCAPS‐1D.

Gao, Yanjie; Liu, Yusong; Guo, Hao; Wen, Huanfei; Li, Zhonghao; Ma, Zongmin; Tang, Jun; Liu, Jun

doi: 10.1002/pssb.202300341pmid: N/A

This article presents a frequency measurement method for spatial microwave signals with solid‐state atom resonance, performing measurements based on the burnt hole in spectrum with two microwave fields acting on nitrogen vacancies (NVs) simultaneously. The population on |0⟩ of the NV color center in the ground state affected by the resonance of two microwave fields with similar frequencies responds excellently to external microwave frequencies, and a phenomenon named hole burning occurs. The full width at half maximum (FWHM) of the resonant peak at the hole is 18.9 kHz. When microwaves of different frequencies are applied, the resonant peak precisely follows the signal frequency in the experiment. Subsequently, the resonant peak is processed using the differential method to obtain a frequency measurement error on the order of 100 Hz. The spatial resolution of this method is within the millimeter scale. This study can provide technical support for applications in microwave frequency measurement and spatial mapping with quantum precision measurement.

Bhandari, Bikash; Yadav, Ashish Kumar; Singh, Rohit; Kiran, G.; Singh, Amit Kumar; Garg, Vivek; Pandey, Sushil Kumar

doi: 10.1002/pssb.202300299pmid: N/A

The gallium antimonide (GaSb) material has very attractive electronic and optoelectronic properties which are suitable for next‐generation infrared (IR) photodetector applications. In this work, properties of undoped GaSb material such as density of states, bandstructure, electron density, absorption coefficient, dielectric function, refractive index, and extinction coefficient are calculated using density‐functional theory (DFT). Moreover, the effects of doping with Ge, Sn, and Zn elements on these properties of GaSb material are investigated. It is found that undoped GaSb material exhibits a direct gap of ≈0.72 eV. Among different doping elements, Ge‐doped GaSb produces a very significant enhancement in optical properties. The Ge‐doped GaSb demonstrates a four times higher absorption coefficient in comparison to undoped GaSb in the IR region at 0.8 eV photon energy. GaSb‐based photodetector device is designed using the Solar Cell Capacitance Simulator (SCAPS) 1D tool. The efficiency of the designed photodetector with optimum thicknesses and doping of different layers is found to be improved from 21.34% to 25.91% after incorporating the absorption data set obtained from the DFT calculations. Additionally, the photodetector with optimum parameters demonstrates maximum responsivity of value ≈0.31 A W−1. In the previous findings, it is demonstrated that GaSb is a very suitable material for next‐generation IR photodetector applications.