We propose a new method for accurately calculating electrical transport properties of a lightly-doped thermoelectric material from density functional theory (DFT) calculations, based on experimental data and density functional theory results for the corresponding undoped material. We employ this approach because hybrid DFT calculations are prohibitive for the large supercells required to model low dopant concentrations comparable to those achieved experimentally for high-performing thermoelectrics. Using zinc antimonide as our base material, we find that the electrical transport properties calculated with DFT and Boltzmann transport theory exhibit the same trends with changes in chemical potential as those computed with hybrid DFT, and propose a fitting algorithm that involves adjusting the computed Fermi energy so that the resulting Seebeck coefficient trends with temperature match experimental trends. We confirm the validity of this approach in reproducing the experimental trends in electrical conductivity and Seebeck coefficient versus temperature for Bi-doped $\beta-$Zn$_4$Sb$_3$. We then screen various transition metal cation dopants, including copper and nickel, and find that a Cu dopant concentration of 2.56% in Zn$_{39}$Sb$_{30}$ exhibited a 14% increase in the thermoelectric power factor for temperatures between 300-400 K. We thus propose that transition metal dopants may significantly improve the thermoelectric performance of the host material, compared to heavy and/or rare-earth dopants.

Alloyed zinc sulfide (ZnS) has shown promise as a relatively inexpensive and earth-abundant transparent conducting material (TCM). Though Cu-doped ZnS has been identified as a high-performing p-type TCM, the corresponding n-doped ZnS has, to date, been challenging to synthesize in a controlled manner; this is because the dopant atoms compete with hole-inducing zinc vacancies near the conduction band minimum as the most thermodynamically stable intrinsic point defects. We thus aim to identify the most promising n-type ZnS-based TCM, with the optimal combination of physical stability, transparency, and electrical conductivity. Using a relatively new method for calculating the free energy of both the sphalerite (cubic) and wurtzite (hexagonal) phases of undoped and doped ZnS, we find that doped ZnS is more stable in the hexagonal structure. This, for the first time, fundamentally explains previous experimental observations of the coexistence of both phases in doped ZnS; hence, it profoundly impacts future work on sulfide TCMs. We also employ hybrid density functional theory calculations and a new carrier transport model, AMSET (ab initio model for mobility and Seebeck coefficient using the Boltzmann transport equation), to analyze the defect physics and electron mobility of the different cation- (B, Al, Ga, In) and anion-doped (F, Cl, Br, I) ZnS, in both the cubic and hexagonal phases, at various dopant compositions, temperatures, and carrier concentrations. Among all doped ZnS candidates, Al-doped ZnS (AZS) exhibits the highest dopant solubility, largest electronic band gap, and highest electrical conductivity of 3830, 1905, and 321 S cm(-1), corresponding to the possible carrier concentrations of n = 10(21), 10(20), and 10(19) cm(-3), respectively, at the optimal 6.25% dopant concentration of Al and the temperature of 300 K.

Accurate models of carrier transport are essential for describing the electronic properties of semiconductor materials. To the best of our knowledge, the current models following the framework of the Boltzmann transport equation (BTE) either rely heavily on experimental data (i.e., semiempirical), or utilize simplifying assumptions, such as the constant relaxation time approximation (BTE-cRTA). While these models offer valuable physical insights and accurate calculations of transport properties in some cases, they often lack sufficient accuracy - particularly in capturing the correct trends with temperature and carrier concentration. We present here a transport model for calculating low-field electrical drift mobility and Seebeck coefficient of n-type semiconductors, by explicitly considering relevant physical phenomena (i.e., elastic and inelastic scattering mechanisms). We first rewrite expressions for the rates of elastic scattering mechanisms, in terms of ab initio properties, such as the band structure, density of states, and polar optical phonon frequency. We then solve the linear BTE to obtain the perturbation to the electron distribution - resulting from the dominant scattering mechanisms - and use this to calculate the overall mobility and Seebeck coefficient. Therefore, we have developed an ab initio model for calculating mobility and Seebeck coefficient using the Boltzmann transport (aMoBT) equation. Using aMoBT, we accurately calculate electrical transport properties of the compound n-type semiconductors, GaAs and InN, over various ranges of temperature and carrier concentration. aMoBT is fully predictive and provides high accuracy when compared to experimental measurements on both GaAs and InN, and vastly outperforms both semiempirical models and the BTE-cRTA. Therefore, we assert that this approach represents a first step towards a fully ab initio carrier transport model that is valid in all compound semiconductors.

Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of significant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Here, we report n-type BaSnO₃ films grown using hybrid molecular beam epitaxy with room temperature conductivity exceeding 10⁴ S cm^-1. Significantly, these films show room temperature mobilities up to 120 cm² V^-1 s^-1 even at carrier concentrations above 3 × 10²⁰ cm^-3 together with a wide bandgap (3 eV). We examine the mobility-limiting scattering mechanisms by calculating temperature-dependent mobility, and Seebeck coefficient using the Boltzmann transport framework and ab-initio calculations. These results place perovskite oxide semiconductors for the first time on par with the highly successful III-N system, thereby bringing all-transparent, high-power oxide electronics operating at room temperature a step closer to reality.

All transparent conducting materials (TCMs) of technological practicality are n-type; the inferior conductivity of p-type TCMs has limited their adoption. In addition, many relatively high-performing p-type TCMs require synthesis temperatures >400 °C. Here, room-temperature pulsed laser deposition of copper-alloyed zinc sulfide (CuxZn1-xS) thin films (0 ≤ x ≤ 0.75) is reported. For 0.09 ≤ x ≤ 0.35, CuxZn1-xS has high p-type conductivity, up to 42 S cm−1 at x = 0.30, with an optical band gap tunable from ≈3.0–3.3 eV and transparency, averaged over the visible, of 50%–71% for 200–250 nm thick films. In this range, synchrotron X-ray and electron diffraction reveal a nanocrystalline ZnS structure. Secondary crystalline CuyS phases are not observed, and at higher Cu concentrations, x > 0.45, films are amorphous and poorly conducting. Within the TCM regime, the conductivity is temperature independent, indicating degenerate hole conduction. A decrease in lattice parameter with Cu content suggests that the hole conduction is due to substitutional incorporation of Cu onto Zn sites. This hole-conducting phase is embedded in a less conducting amorphous CuyS, which dominates at higher Cu concentrations. The combination of high hole conductivity and optical transparency for the peak conductivity CuxZn1-xS films is among the best reported to date for a room temperature deposited p-type TCM.

Tin monosulfide (SnS) is an emerging thin-film absorber material for photovoltaics. An outstanding challenge is to improve carrier lifetimes to >1 ns, which should enable >10% device efficiencies. However, reported results to date have only demonstrated lifetimes at or below 100 ps. In this study, we employ defect modeling to identify the sulfur vacancy and defects from Fe, Co, and Mo as most recombination-active. We attempt to minimize these defects in crystalline samples through high-purity, sulfur-rich growth and experimentally improve lifetimes to >3 ns, thus achieving our 1 ns goal. This framework may prove effective for unlocking the lifetime potential in other emerging thin-film materials by rapidly identifying and mitigating lifetime-limiting point defects.