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Roles of Carrier Doping, Band Gap, and Electron Relaxation Time in the Boltzmann Transport Calculations of a Semiconductor’s Thermoelectric Properties
摘要： Although there is a growing demand for first-principles predictions of the thermoelectric properties of materials, the contribution of various errors in Boltzmann transport calculations is not negligible. We conducted a typical first-principles calculation and a Boltzmann transport analysis on a typical semiconductor (Si) at various temperatures T while varying the band gap ?g, electron relaxation time ?el, and phonon thermal conductivity ?ph to demonstrate how the calculated thermoelectric properties, which are functions of the carrier doping level, are affected by these parameters. Bipolar conduction drastically decreased zT via a degradation of the Seebeck coefficient S and an increase in the effective Lorenz factor Leff, indicating the importance of a wide enough ?g (several multiples of kBT or higher) for high zT. Thus, the underestimation of ?g, which frequently happens in first-principles calculations, could induce large errors in calculations for narrow-gap semiconductors. The calculation of the electron thermal conductivity without Peltier thermal conductivity was found to limit the zT of typical semiconductors to below 1. A small value of ?ph/?el, where ?ph/?el is the degree to which a material is a phonon-glass electron-crystal, was necessary to achieve a high zT. Fitting the calculations with experimental thermoelectric properties showed that ?el can vary by an order of magnitude from 10115 to 10114 s, depending on both T and the samples. This indicates that the use of a fixed relaxation time is inappropriate for thermoelectric materials.
关键词： Boltzmann transport calculation,first-principles calculation,thermoelectric properties
更新于2025-09-23 15:23:52
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Defect formation of CuI-doped by group-IIB elements
摘要： First-principles calculations have been performed to investigate the doping defects in CuI with group-IIB elements such as Zn, Cd and Hg. The calculated transition energies for substitutional Zn, Cd and Hg are 1.32, 1.28 and 0.60 eV, respectively. These group-IIB elements at the substitutional sites complex with a copper vacancy (VCu) have the lower formation energies as compared to dopants located at the substitutional sites or interstitial sites, respectively. Among all the complex defects considered, [HgCu + VCu] has the lowest formation energy and it induces the acceptor level ε(0/?) = 0.18 eV above the valence-band maximum (VBM), which is close to the acceptor level ε(0/?) = 0.1 eV of VCu, suggesting that Hg may be a good dopant for CuI to improve its p-type conductivity.
关键词： group-IIB elements,defects formation,first-principles calculation,Semiconductor
更新于2025-09-23 15:23:52
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Air-stable N-doped black phosphorus transistor by thermal deposition of metal adatoms
摘要： In this work, a simple and effective thermal deposition method is described to enhance the stability and achieve n-doping of two-dimensional black phosphorus (BP), resulting the successful fabrication of logic devices. By doping with Al adatoms, the stability of BP against oxidation is enhanced and the transfer characteristics are maintained for several days under ambient conditions. Furthermore, the resulting BP is n-doping showing a negative-shifted threshold voltage and enhanced electron mobility. The mechanism of Al doping is investigated by first-principles calculation and Al induces a downward shift of the conduction band minimum and increases the Femi level. In addition, integration of bare BP and Al-doped BP enables the fabrication of various logic devices such as inverters and p?n diodes. This work reveals a facile strategy to simultaneously enhance the stability and regulate the conductivity of BP by doping with metal adatoms boding well for device applications.
关键词： n-doping,stability,black phosphorus,thermal deposition,first-principles calculation
更新于2025-09-23 15:23:52
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Adsorption of hazardous gases in nuclear islands on monolayer MoS2 sheet
摘要： Monitoring and removing the hazardous gases (such as radioactive gases and hydrogen) in the nuclear islands are full with enormous challenges, although the two methods can improve the safety level of the nuclear power plant. Due to its excellent electronic and chemical properties, two dimensional materials are considered as the candidate for monitoring and removing the hazardous gases in the nuclear islands. In this paper, the adsorption of the hazardous gases on monolayer MoS2 sheet was investigated by using the first principles calculation method. The adsorption energy, total charge transfer, and density of states (DOS) were calculated to understand the adsorption mechanism and sensing performance of the monolayer MoS2 sheet to the hazardous gases. The results show that an attractive interaction exists between the hazardous gases and the monolayer MoS2 sheet. The magnitude of the adsorption energy demonstrates that physisorption dominates the adsorption of the hazardous gas molecules on the monolayer MoS2 sheet, but the adsorption of the dissociated H/I atom belongs to chemisorption. The DOS shows that the orbitals, H 1s and I 5p, play a crucial role in the adsorption, and the change of the electronic structure indicates that the monolayer MoS2 sheet might be a promising material which is used for monitoring the gaseous radioactive iodine in the nuclear islands.
关键词： Hydrogen,Hazardous gases,Radioactive gases,First principles calculation,Monolayer MoS2 sheet
更新于2025-09-23 15:23:52
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Infrared Spectroscopy on Electronic Structures of Platinum-group Metal Pernitrides MN2 (M = Ru, Rh, Ir, and Pt)
摘要： The electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and Pt) were investigated via synchrotron radiation infrared spectroscopy and first-principles calculations. Measured reflectance spectra of marcasite-type RuN2 and RhN2 showed Drude-like responses, approaching 1 as the photon energy was decreased, whereas reflectance of arsenopyrite-type IrN2 and pyrite-type PtN2 became ~0.3 in the low photon energy region with a few features. These findings agreed well with the predictions of the metallic nature of marcasite-type RuN2 and RhN2 and the semiconducting properties of arsenopyrite-type IrN2 and pyrite-type PtN2, respectively. The measured reflectance spectra were also reasonably consistent with the calculated optical responses. The band gaps of IrN2 and PtN2 were estimated to be 0.8 and 2.1 eV, respectively, via first-principles calculation with a modified Becke–Johnson (MBJ) potential for the exchange potential.
关键词： first-principles calculation,platinum-group metal pernitride,infrared reflectance spectra,valence band electronic structure
更新于2025-09-23 15:22:29
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The phase transition and optical properties of Cr2+-doped ZnSe under high pressure
摘要： The phase transition pressure, electronic structure, optical properties and stability for ZnSe and Cr2+:ZnSe with different doping concentrations were calculated by first-principles calculation based on density-functional theory. The phase transition pressure was calculated by enthalpy-pressure relation. The introduction of dopant (Cr2+) reduces the phase transition pressure, and the phase transition pressure decreases with the increase of doping concentration. The high pressure enhances the degeneracy of Cr-d orbitals. Under the high-pressure conditions, the absorption peak positions of Cr2+:ZnSe have obvious blue-shift. Meanwhile, the stability of structures for ZnSe and Cr2+:ZnSe were further confirmed by defect formation energy and elastic constants.
关键词： Phase transition pressure,Cr2+:ZnSe,First-principles calculation,Optical properties
更新于2025-09-23 15:22:29
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A theoretical investigation of the glide dislocations in the sphalerite ZnS
摘要： The 90(cid:1) and 30(cid:1) partial glide dislocations in ZnS are investigated theoretically in the framework of the fully discrete Peierls model and first-principles calculation. It is found that there are four types of equilibrium cores for each kind of partial glide dislocation, which are named as the O-Zn-core, the B-Zn-core, the O-S-core, and the B-S-core, according to their geometrical feature and atomic ingredient at the core. For the 90(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-S-core (single-period core) are stable. The Peierls barrier heights of the O-Zn-core and the B-S-core are about 0:03 eV/? and 0:01 eV/?, respectively. For the 30(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-Zn-core (single-period core) are stable and their Peierls barrier heights are approximately the same as that of the O-Zn-core of the 90(cid:1) partial dislocation. The Peierls stress related to the barrier height is about 800 MPa for the 90(cid:1) partial dislocation with the B-S-core. The existence of unstable equilibrium cores enables us to introduce the concept of the partial kink. Based on the concept of the partial kink, a minimum energy path is proposed for the formation and migration of kinks. It is noticed that the step length in kink migration is doubled due to the core reconstruction.
关键词： glide dislocations,sphalerite ZnS,Peierls model,partial kink,first-principles calculation
更新于2025-09-23 15:21:21
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Structural determination of phosphosilicate glass based on first-principles molecular dynamics calculation
摘要： We report static and dynamic first-principles calculations determining the structure and electronic properties of phosphosilicate glass (PSG). A stable structure of PSG with composition of (SiO2)x(P2O5)y was calculated by simulated annealing based on Car–Parrinello molecular dynamics (CPMD) with a real-space density functional theory (RSDFT) code. As a result, phosphorus (P) atoms in PSG were four-fold coordinated with oxygen (O) atoms and one of the four PO bonds was dangling toward the interstitial region (an –O3PO configuration). We also compared the structures having a different number of O atoms to discuss the stable configuration of PSG in the realistic situation of phosphoryl chloride (POCl3) annealing. We found that –O3PO is most stable for O2-rich conditions, whereas three-coordinate P (an –O3P configuration) becomes stable in O2-poor conditions. The candidates of the states which create levels inside the bandgap of PSG were also calculated.
关键词： phosphosilicate glass,molecular dynamics,first-principles calculation,electronic properties,POCl3 annealing
更新于2025-09-23 15:21:21
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Improvement of the Laser-Welded Lap Joint of Dissimilar Mg Alloy and Cu by Incorporation of a Zn Interlayer
摘要： During pulsed laser welding of AZ 31B magnesium (Mg) alloy and T2 pure copper (Cu), Cu2Mg and Mg2Cu are generated, but the bonding ability of the two compounds is usually weak, resulting in low strength. In order to improve the joint of two dissimilar metals, a zinc interlayer was inserted between the Mg alloy and Cu, and the effects of the thickness of the Zn interlayer on the microstructure and properties of the joint were studied. The fused zone consisted of Cu2Mg and MgZn, and, according to first-principles calculation, in the same energy range, the area enclosed by the density of the state curve of MgZn was larger than that of Cu2Mg. Hence, the bonding ability of MgZn was better than that of Cu2Mg, and MgZn improved the strength of the welded joint. The most advantageous thickness of the Zn interlayer was 0.1 mm, and the shear strength was 48.15 MPa that was 161% higher than that of the directly welded Mg/Cu joint.
关键词： interlayer,first-principles calculation,magnesium alloy,laser welding,dissimilar metals
更新于2025-09-23 15:21:01
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revealed by resonant photoelectron spectroscopy
摘要： Resonant photoelectron spectroscopy at the Co and Mn 2p core absorption edges of half-metallic Co2MnGe has been performed to determine the element-speci?c density of states (DOS). A signi?cant contribution of the Mn 3d partial DOS near the Fermi level (EF) was clari?ed by measurement at the Mn 2p absorption edge. Further analysis by ?rst-principles calculation revealed that it has t2g symmetry, which must be responsible for the electrical conductivity along the line perpendicular to the ?lm plane. The dominant normal Auger contribution observed at the Co 2p absorption edge indicates delocalization of photoexcited Co 3d electrons. The difference in the degrees of localization of the Mn 3d and Co 3d electrons in Co2MnGe is explained by the ?rst-principles calculation. Our ?ndings of the element-/orbital-speci?c electronic states near EF will pave the way for future interface design of magnetic tunneling junctions to overcome the temperature-induced reduction of the magnetoresistance.
关键词： first-principles calculation,magnetic tunneling junctions,normal Auger contribution,half-metallic Co2MnGe,magnetoresistance,Resonant photoelectron spectroscopy,Mn 3d partial DOS,element-speci?c density of states,electrical conductivity
更新于2025-09-11 14:15:04