arXiv subjects

Shang-Peng Gao

Publications and source records attributed to Shang-Peng Gao.

6 recordsLinked to original sources

arXiv2026

Exceptionally high carrier mobility in hexagonal diamond

Hexagonal diamond (h-diamond), or Lonsdaleite, is a promising wide-bandgap semiconductor known for its high thermal conductivity and hardness. Based on \textit{ab initio} calculations, we demonstrate its exceptionally high carrier mobilities. At room temperature, the hole mobilities along the $\perp c$ and $\parallel c$ directions are 6000 and 6024 cm$^{2}$V$^{-1}$s$^{-1}$, respectively, while the corresponding electron mobilities reach 12339 and 28473 cm$^{2}$V$^{-1}$s$^{-1}$. These values are significantly superior to those of most known semiconductors, including cubic diamond. The small effective masses in h-diamond are comparable to those in the cubic phase, which cannot explain its substantially higher mobilities. Instead, two underlying mechanisms are uncovered. First, selection rules enforced by the symmetry of h-diamond significantly suppress scattering, particularly for transverse acoustic phonons, which predominate in the cubic phase around room temperature. Secondly, the spatial mismatch between the electronic wavefunctions and phonon-induced scattering potentials leads to real-space electron-phonon decoupling, which manifests as the suppression of out-of-plane polarised longitudinal acoustic scattering for holes, and a systematic weakening of acoustic scattering for electrons.

cond-mat.mtrl-sci↗

arXiv2026

Hybrid functional calculation of electrical activity and complexing mechanism of Cu-related defects

Copper is a detrimental impurity in silicon with high diffusivity and a high tendency to precipitate. Interaction between Cu and other defects is essential for understanding the nature of Cu precipitation in silicon. Despite extensive experimental investigations of Cu-related defects in silicon, a comprehensive understanding remains elusive due to limitations of techniques in resolving defect configurations, as well as inconsistencies between theoretical and experimental results regarding transition levels. Moreover, the underlying formation mechanism of the well-known $\mathrm{Cu_{PL}}$ line is still unclear. In this work, configurations, formation energies, and transition levels of Cu-related defects in silicon are calculated using the HSE06 functional and finite-size correction. Defects involved in this study include $\mathrm{Cu_i}$, $\mathrm{Cu_{Si}}$, Cu-B, Cu-P, and Cu-H. A $\mathrm{Cu_{i4}V}$ model is proposed to explain the discrepancies between theory and experiment about $\mathrm{Cu_{PL}}$ defect. Our calculations may provide insight into the electrically active defects and the early states of Cu precipitation in silicon.

cond-mat.mtrl-sci↗

arXiv2025

First-principles Prediction of Carrier Mobility in Semiconductor Nanowires Based on the Spatially Dependent Boltzmann Transport Equation

Carrier mobility in bulk semiconductors is typically governed by electron-phonon (e-ph) scattering. In nanostructures, spatial confinement can lead to significant surface scattering, lowering mobility and breaking the spatial homogeneity assumption of conventional models. In this work, a fully ab initio framework based on the spatially dependent Boltzmann transport equation for one-dimensional nanowires is developed. We apply it to Si and GaN assuming diffusive surface scattering, and reveal the mobility-diameter relation: $μ_\mathrm{1D} = μ_\mathrm{bulk} \left[1-\left(d/d_0\right)^{-β}\right]$. The parameter $d_0$, comparable to the carrier mean free path, defines a boundary layer exhibiting a considerable mobility gradient, and also quantifies the competition between e-ph and surface scattering together with $β$. We further discuss the effects of orientation, cross-sectional shape, and temperature. Moreover, experimental data are generally lower than our predictions, possibly due to structural imperfections, systematic errors from measurements, etc. Therefore, our theoretical method can provide an intrinsic benchmark toward optimized experimental realizations.

cond-mat.mtrl-sci↗

arXiv2021

A method to restore the intrinsic dielectric functions of 2D materials in periodic calculations and its applications to the dielectric and optical properties of ultrathin h-BN and MoS2

Previous calculations of the dielectric and optical properties of 2D materials often overlooked or circumvented the influence of vacuum spacing introduced in periodic calculations, which gave rise to mispredictions of the intrinsic properties of 2D materials or merely qualitative results. We first elucidate the relationship between the vacuum spacing and the dielectric and optical properties of 2D materials in periodic calculations, and then bring forward an effective method to accurately predict the dielectric and optical properties of 2D materials by restoring the intrinsic dielectric functions of 2D materials independent of the additional vacuum spacing. As examples, the intrinsic dielectric and optical properties of ultrathin h-BN and MoS2 from monolayer to pentalayer, including dielectric functions, optical absorption coefficients, refraction indexes, reflectivities, extinction coefficients, and energy loss functions, have been calculated by our method. Our calculations reveal that the out-of-plane optical dielectric constants, static refraction indexes, and static reflectivities of 2D h-BN and MoS2 increase as the number of layers increases, while the in-plane counterparts remain unchanged. Excitonic frequency-dependent optical properties of h-BN and MoS2 from monolayer to bulk are also calculated by solving the Bethe-Salpeter equation and show strong anisotropy. In better agreement with experimental results than previous calculations, the presented method demonstrates enormous potential to investigate the dielectric and optical properties of other 2D materials extensively and quantitively.

cond-mat.mtrl-sci↗

arXiv2015

Tuning the electronic structures of silicene and germanene by biaxial strain and electric field

We present a first-principles study of effects of small biaxial strain ($|\varepsilon|\le 5\%$) and perpendicular electric field (E-field) on the electronic and phonon properties of low-buckled silicene and germanene. With an increase of the biaxial strain, the conduction bands at the high symmetric $Γ$ and $M$ points of the first Brillouin zone shift significantly towards the Fermi level in both silicene and germanene. In contrast, the E-field changes the band dispersions near the $Γ$ and open a small band gap at the K point in silicene. We found that the field-induced gap opening in silicene could be enhanced by a compressive strain while mitigated by a tensile strain. This result highlights the tunability of the electronic structures of silicene by combining the mechanical strain and the electric field.

cond-mat.mtrl-sci↗

arXiv2013

The stability, electronic structure, and optical property of TiO2 polymorphs

Phonon density of states calculation shows that a new TiO2 polymorph with tridymite structure is mechanically stable. Enthalpies of 9 TiO2 polymorphs under different pressure are presented to study the relative stability of the TiO2 polymorphs. Band structures for the TiO2 polymorphs are calculated by density functional theory with generalized gradient approximation and the band energies at high symmetry k-points are corrected using the GW method to accurately determine the band gap. The differences between direct band gap energies and indirect band gap energies are very small for rutile, columbite and baddeleyite TiO2, indicating a quasi-direct band gap character. The band gap energies of baddeleyite (quasi-direct) and brookite (direct) TiO2 are close to that of anatase (indirect) TiO2. The band gap of the newly predicted tridymite-structured TiO2 is wider than the other 8 polymorphs. For optical response calculations, two-particle effects have been included by solving the Bethe-Salpeter equation for Coulomb correlated electron-hole pairs. TiO2 with cotunnite, pyrite, and fluorite structures have optical transitions in the visible light region.

cond-mat.mtrl-sci↗