We present a first-principles framework to extract deformation potentials in silicon based on density-functional theory (DFT) and density-functional perturbation theory (DFPT). We compute the electronic band structures, phonon dispersion relations, and electron-phonon matrix elements to extract deformation potentials for acoustic and optical phonons for all possible processes. The matrix elements clearly show the separation between intra- and intervalley scattering in the conduction band, and quantify the strength of the scattering events in the degenerate bands of the valence band. We then use an advanced numerical Boltzmann transport equation (BTE) simulator that couples DFT electronic structures and energy/momentum-dependent scattering rates to compute the transport properties for electrons and holes. By incorporating ionized impurity scattering as well, we calculate the $n$-type and $p$-type mobility versus carrier density and make comparisons to experiments, indicating excellent agreement. The fact that the method we present uses well-established theoretical tools and requires the extraction of only a limited number of matrix elements, makes it generally computationally very attractive, especially for semiconductors with a large unit cell and lower symmetry.

We theoretically investigate thermal conductivity in silicon nanomeshes using Monte Carlo simulations of phonon transport. Silicon membranes of 100 nm thickness with randomly located pores of 50 nm diameter are considered. The effects of material porosity and pore surface roughness are examined. Nanomesh porosity is found to have a strong detrimental effect on thermal conductivity. At room temperature, a porosity of 50% results in ∼80% reduction in thermal conductivity. Boundary roughness scattering further degrades thermal conductivity, but its effect is weaker. Thermal transport can additionally be affected by the specific arrangement of the pores along the transport direction.

Mobility is a key parameter for SnO₂, which is extensively studied as a practical transparent oxide n-type semiconductor. In experiments, the mobility of electrons in bulk SnO₂ single crystals varies from 70 to 260 cm²V⁻¹s⁻¹ at room temperature. Here, we calculate the mobility as limited by electron–phonon and ionized impurity scattering by coupling the Boltzmann transport equation with density functional theory electronic structures. The linearized Boltzmann transport equation is solved numerically beyond the commonly employed constant relaxation-time approximation by taking into account all energy and momentum dependencies of the scattering rates. Acoustic deformation potential and polar optical phonons are considered for electron–phonon scattering, where polar optical phonon scattering is found to be the main factor which determines the mobility of both electrons and holes at room temperature. The calculated phonon-limited electron mobility is found to be 265 cm²V⁻¹s⁻¹, whereas that of holes is found to be 7.6 cm²V⁻¹s⁻¹. We present the mobility as a function of the carrier concentration, which shows the upper mobility limit. The large difference between the mobilities of n-type and p-type SnO₂ is a result of the different effective masses between electrons and holes.

We investigate topological phases of monolayer jacutingaite (${\mathrm{Pt}}_2{\mathrm{HgSe}}_3$) that arise when considering the competing effects of spin-orbit coupling (SOC), magnetic exchange interactions, and staggered sublattice potential $V$. The interplay between the staggered potential and exchange field offers the possibility of attaining different topological phases. By analyzing the Berry curvatures and computing the Chern numbers and Hall conductivities, we demonstrate that the system is time-reversal-symmetry-broken quantum spin Hall insulator when $m_b<{\lambda }_{\mathrm{so}}$, where $m_b$ is the exchange field operating on the bottom Hg sublattice and ${\lambda }_{\mathrm{so}}$ is the intrinsic SOC. For $m_b>{\lambda }_{\mathrm{so}}$ and in the presence of Rashba SOC, we find that the band gap at valley $K\left(K^{\prime }\right)$ is topologically trivial (nontrivial) with Chern number $\mathcal{C}=1$ and valley Chern number ${\mathcal{C}}_v=-1$, indicating that the system is valley-polarized quantum anomalous Hall insulator. We show that the topology of each valley is swapped (the Chern number becomes $\mathcal{C}=-1$) by reversing the sign of the exchange field. The system transitions to a valley-polarized metal and quantum valley Hall phase as $V$ increases. Along the phase boundaries, we observe a single Dirac-cone semimetal states. These findings shed more light on the possibility of realizing and controlling topological phases in spintronics and valleytronics devices.

Metals have high electronic conductivities, but very low Seebeck coefficients, which traditionally make them unsuitable for thermoelectric materials. Recent studies, however, showed that metals could deliver ultrahigh thermoelectric power factors (PFs) under certain conditions. In this work, we theoretically examine the electronic structure and electronic transport specifications that allow for such high PFs. Using Boltzmann transport equation (BTE) simulations and a multiband electronic structure model, we show that metals with (i) a high degree of transport asymmetry between their bands, (ii) strong interband scattering, and (iii) a large degree of band overlap, can provide ultrahigh power factors. We show that each of these characteristics adds to the steepness of the transport distribution function of the BTE, which allows for an increase of the Seebeck coefficient to sizable values, with an increase in the electrical conductivity. This work generalizes the concept that transport asymmetry (i.e., a mixture of energy regions of high and low contributions to the electrical conductivity), through a combination of different band masses, scattering strengths, energy filtering scenarios, etc., can indeed result in very high thermoelectric power factors, even in the absence of a material band gap. Under certain conditions, transport asymmetry can overcompensate for any performance degradation to the PF due to bipolar conduction and the naturally low Seebeck coefficients that otherwise exist in this class of materials. Published by the American Physical Society 2024