Electron-phonon scattering effect on the lattice thermal conductivity of silicon nanostructures

Unveiling Superior Solar-Blind Photodetection with a NiO/ZnGa2O4 Heterojunction Diode

This investigation presents a self-powered, solar-blind photodetector utilizing a low-temperature fabricated crystalline NiO/ZnGa2O4 heterojunction with a staggered type-II band alignment. The device leverages the pyrophototronic effect (PPE), combining the photoelectric effect in the p-n junction and the pyroelectric effect in the non-centrosymmetric ZnGa2O4 crystal. This synergistic effect enhances the photodetector's performance parameters, thereby outperforming traditional solar-blind photodetectors. The device demonstrates an extremely low dark current of 5.39 fA, a high responsivity of 88 mA/W, and a very high specific detectivity of 2.03 × 1014 Jones under 246 nm light irradiation at 0 V bias. Significantly, due to the PPE, the impact demonstrates a much-enhanced transient response when tested under various light intensities, ranging from 18 to 122 μW/cm2. The photodetector shows a high responsivity of 338 A/W and an outstanding detectivity of 7.1 × 1018 Jones with an applied voltage of -13 V, showing its ability to detect weak signals. Single-crystalline ZnGa2O4 fabricated by MOCVD exhibits significant absorption of deep UV light, and the heterojunction's type-II band alignment with NiO is responsible for its exceptional self-powered pyrophotoelectric detecting and rectifying capabilities.

Strain Effects on the Electronic and Thermoelectric Properties of n(PbTe)-m(Bi2Te3) System Compounds

Owing to their low lattice thermal conductivity, many compounds of the n(PbTe)-m(Bi2Te3) homologous series have been reported in the literature with thermoelectric (TE) properties that still need improvement. For this purpose, in this work, we have implemented the band engineering approach by applying biaxial tensile and compressive strains using the density functional theory (DFT) on various compounds of this series, namely Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5. All the fully relaxed Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5 compounds are narrow band-gap semiconductors. When applying strains, a semiconductor-to-metal transition occurs for all the compounds. Within the range of open-gap, the electrical conductivity decreases as the compressive strain increases. We also found that compressive strains cause larger Seebeck coefficients than tensile ones, with the maximum Seebeck coefficient being located at −2%, −6%, −3% and 0% strain for p-type Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5, respectively. The use of the quantum theory of atoms in molecules (QTAIM) as a complementary tool has shown that the van der Waals interactions located between the structure slabs evolve with strains as well as the topological properties of Bi2Te3 and PbBi2Te4. This study shows that the TE performance of the n(PbTe)-m(Bi2Te3) compounds is modified under strains.

Hydrostatic Pressure Tuning of Thermal Conductivity for PbTe and PbSe Considering Pressure-Induced Phase Transitions

Flexibly modulating thermal conductivity is of great significance to improve the application potential of materials. PbTe and PbSe are promising thermoelectric materials with pressure-induced phase transitions. Herein, the lattice thermal conductivities of PbTe and PbSe are investigated as a function of hydrostatic pressure by first-principles calculations. The thermal conductivities of both PbTe and PbSe in NaCl phase and Pnma phase exhibit complex pressure-dependence, which is mainly ascribed to the nonmonotonic variation of a phonon lifetime. In addition, the thermal transport properties of the Pnma phase behave anisotropically. The thermal conductivity of Pnma-PbTe is reduced below 1.1 W/m·K along the c-axis direction at 7-12 GPa. The mean free path for 50% cumulative thermal conductivity increases from 7 nm for NaCl-PbSe at 0 GPa to 47 nm for the Pnma-PbSe in the a-axis direction at 7 GPa, making it convenient for further thermal conductivity reduction by nanostructuring. The thermal conductivities of Pnma-PbTe in the c-axis direction and Pnma-PbSe in the a-axis direction are extremely low and hypersensitive to the nanostructure, showing important potential in thermoelectric applications. This work provides a comprehensive understanding of phonon behaviors to tune the thermal conductivity of PbTe and PbSe by hydrostatic pressure.

Electron–phonon scattering and excitonic effects in T-carbon

Through first-principles calculations combining many-body perturbation theory, we investigate electron–phonon scattering and optical properties including the excitonic effects of T-carbon. Our results reveal that optical and acoustic phonons dominate the scattering around the valence and the conduction band edges, respectively. In addition, the relaxation lifetimes of holes (0.5 ps) are longer than those of electrons (0.24 ps) around the band edges due to the weaker scattering. We also predict that mean free paths of hot holes are as high as 80 nm while only 15 nm for hot electrons, resulting in different hot carrier extraction ranges in T-carbon. Moreover, we demonstrate that there exist lowest energy dark excitons in T-carbon with radiative lifetime of about 3.4 s, which is revealed to be much longer than that of bright excitons and would lower the photoluminescence quantum yield of T-carbon.

Through first-principles calculations combining many-body perturbation theory, we investigate electron–phonon scattering and optical properties including the excitonic effects of T-carbon.

Improvement in the thermoelectric properties of porous networked Al-doped ZnO nanostructured materials synthesized via an alternative interfacial reaction and low-pressure SPS processing

This work presents a novel, simpler and faster bottom-up approach to produce relatively high performance thermoelectric Al-doped ZnO ceramics from nanopowders produced by interfacial reaction followed by consolidation with Spark Plasma Sintering.

Bulk Polymer-Derived Ceramic Composites of Graphene Oxide

Bulk polymer-derived ceramic (PDC) composites of SiCO with an embedded graphene network were produced using graphene-coated poly(vinyl alcohol) (PVA) foams as templates. The pyrolysis of green bodies containing cross-linked polysiloxane, PVA foams, and graphene oxide (GO) resulted in the decomposition of PVA foams, compression of GO layers, and formation of graphitic domains adjacent to GO within the SiCO composite, leading to SiCO composites with an embedded graphene network. The SiCO/GO composite, with about 1.5% GO in the ceramic matrix, offered an increase in the electrical conductivity by more than 4 orders of magnitude compared to that of pure SiCO ceramics. Additionally, the unique graphene network in the SiCO demonstrated a drop in the observed thermal conductivity of the composite (∼0.8 W m^-1 K^-1). Young's modulus of the as-fabricated SiCO/GO composites was found to be around 210 MPa, which is notably higher than the reported values for similar composites fabricated from only ceramic precursors and PVA foams. The present approach demonstrates a facile and cost-effective method of producing bulk PDC composites with high electrical conductivity, good thermal stability, and low thermal conductivity.