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This study investigated the low contact resistivity and Schottky barrier characteristics in p-GaN by modifying the thickness and doping levels of a p-InGaN cap layer. A comparative analysis with highly doped p-InGaN revealed the key mechanisms contributing to low-resistance contacts. Atomic force microscopy inspections showed that the surface roughness depends on the doping levels and cap layer thickness, with higher doping improving the surface quality. Notably, increasing the doping concentration in the p++-InGaN cap layer significantly reduced the specific contact resistivity to 6.4 ± 0.8 × 10−6 Ω·cm2, primarily through enhanced tunneling. Current–voltage (I–V) characteristics indicated that the cap layer’s surface properties and strain-induced polarization effects influenced the Schottky barrier height and reverse current. The reduction in barrier height by approximately 0.42 eV in the p++-InGaN layer enhanced hole tunneling, further lowering the contact resistivity. Additionally, polarization-induced free charges at the metal–semiconductor interface reduced band bending, thereby enhancing carrier transport. A transition in current conduction mechanisms was also observed, shifting from recombination tunneling to space-charge-limited conduction across different voltage ranges. This research underscores the importance of doping, cap layer thickness, and polarization effects in achieving ultra-low contact resistivity, offering valuable insights for improving the performance of p-GaN-based power devices.

GaN-based Micro-LEDs, representative devices of third-generation wide-bandgap semiconductors, exhibit significant nonlinear photoluminescence (PL) properties under ultrafast femtosecond laser excitation, governed predominantly by multiphoton absorption processes. In this study, we systematically investigate photocarrier transport and recombination dynamics under various bias voltages and excitation powers using an ultrafast (∼7.5 fs) femtosecond spectroscopy system. Experimental results indicate that applying forward bias enhances PL emission dramatically by promoting radiative recombination within localized states in quantum wells, due to increased quantum-well energy-band tilting. Conversely, a reverse bias flattens the quantum-well band structure, significantly facilitating carrier drifting, thereby suppressing radiative recombination and enhancing photovoltage responses. The power-dependent analysis further reveals that nonlinear PL responses exhibit power law fitting slopes consistently greater than 2, confirming the active involvement of multiphoton absorption mechanisms. Based on these findings, a comprehensive “field modulation - nonlinear excitation” model is proposed, providing essential theoretical insights and experimental support for the future design and optimization of high-speed optoelectronic devices and highly integrated Micro-LED display applications.

By employing a graded-interfaces model based on a generalized formalism for interface-roughness (IFR) scattering that was modified for mid-infrared emitting quantum cascade lasers (QCLs), we have accurately reproduced the electro-optical characteristics of published record-performance 4.9 µm- and 8.3 µm-emitting QCLs. The IFR-scattering parameters at various interfaces were obtained from measured values and trends found via atom-probe tomography analysis of one of our 4.6 μm-emitting QCL structures with variable barrier heights. Those values and trends, when used for designing a graded-interface, 4.6 μm-emitting QCL, led to experimental device characteristics in very good agreement with calculated ones. We find that the published record-high performance values are mainly due to both injection from a prior-stage low-energy (active-region) state into the upper-laser ( ) level, thus at low field-strength values, as well as to strong photon-induced carrier transport. However, the normalized leakage-current density is found to be quite high: 26–28 % and 23.3 %, respectively, mainly because of IFR-triggered shunt-type leakage through high-energy active-region states, in the presence of high average electron temperatures in the laser level and an energy state adjacent to it: 1060 K and 466 K for 4.9 µm- and 8.3 µm-emitting QCLs, respectively. Then, modeling with graded interfaces becomes a tool for designing devices of performances superior to the best reported to date, thus closing in on fundamental limits. The model is employed to design a graded-interface 8.1 µm-emitting QCL with suppressed carrier leakage via conduction-band engineering, which reaches a maximum front-facet wall-plug efficiency value of 22.2 %, significantly higher than the current record (17 %); thus, a value close to the fundamental front-facet, upper limit (i.e., 25 %) for ∼8 µm-emitting QCLs.

Eumelanin, the brown-black member of the melanin family of biopigments, has emerged as a promising material for sustainable organic electronics. Sepia eumelanin develops hierarchically from (5, 6)-dihydroxyindole (DHI) and (5, 6)-dihydroxyindole-2-carboxylic acid (DHICA) monomers, and its structure is made up of granules with typical size in the 100–300 nm range. Literature reports that Sepia eumelanin (from now on indicated as Sepia melanin), derived from the ink sac of cuttlefish, exhibits predominant electronic transport in dry state and mixed ionic–electronic transport in its hydrated state when studied at millimetric or micrometric distance ranges. To explore the upper limit of the conductivity of Sepia melanin and unlock its full technological potential, we investigated its electrical response at the nanoscale where the influence of granule boundaries is expected to be minimal. Using electrodes patterned at the nanoscale by e-beam lithography, we run current–voltage, current–time and electrochemical impedance spectroscopy measurements; we observed predominant electronic transport mechanisms in Sepia melanin, with conductivities that increase as the interelectrode distance decreases. Temperature-resolved experiments permitted us to deduce the transport activation energy. Our work highlights the importance of exploring the electrical response of natural materials across varying distance scales to exploit their full potential for sustainable organic electronics.

A polypyrrole-single-walled carbon nanotube (PPY-SWCNT) has been prepared with 5 wt.% of single-walled carbon nanotubes (SWCNT) employing chemical oxidative in situ polymerization to compare the thermoelectric properties of polypyrrole (PPY) and the composite. The composite formation has been discussed based on the carrier transport mechanism through the composite. Transport parameters have been calculated and correlated with the structure formation. Dependence of carrier concentration and mobility of charge carrier on temperature has been obtained based on the charge carrier transport in PPY and PPY-SWCNT composite.

Magneto-transport study has been performed in ZrTe5 single crystals. The observed Shubnikov-de Hass quantum oscillation at low temperature clearly demonstrates the existence of a nontrivial band with small effective mass in ZrTe5. Furthermore, we also revealed the highly anisotropic nature of high-field Landau level splitting in ZrTe5, suggesting the dominant role of orbital contribution to the splitting. Besides these, an abnormal large enhancement of magnetoresistance appears at high temperatures, which is believed to arise from the Lifshitz transition induced two-carrier transport in ZrTe5. Our study provides more understanding of the physical properties of ZrTe5 and sheds light on potential application of ZrTe5 in spintronics.

The results of a specific modelling technique for perovskite (PVK)-based solar cells under preconditioned AM1.5 illumination for various device architectures are presented in this work. The widely used PVK material of MAPbI 3 has certain architectural issues, such as volatility and instability due to the presence of methylammonium (MA). To deal with such issues, replacing MA with Cesium can provide a stable PSC device. The primary goal of this research is to optimize the thickness parameters of the methylammonium-free PVK active layer, i.e., Caseium lead iodide (CsPbI 3 ) and the carrier transport layers (CTLs). The current simulation uses TiO 2 and Spiro-OMeTAD as the CTLs to sandwich the CsPbI 3 layer, which has a wide bandgap of 1.73 eV. Moreover, the better fabrication temperature and defectivity analysis for the perovskite solar cell are also investigated. Due to the high open-circuit voltage for the Casieum-based PSC devices offers an optimized power conversion efficiency, reaching nearly 25%, which can be beneficial for reasonable fabrication of the PSC device.

Perovskite solar cells (PSCs), one of the most promising photovoltaic technologies, have been widely studied due to their high power conversion efficiency (PCE), low cost, and solution processability. The architecture of PSCs determines that high PCE and stability are highly dependent on each layer and the related interface, where nonradiative recombination occurs. Conventional synthetic chemical materials as modifiers have disadvantages of being toxic and costly. Natural molecules with advantages of low cost, biocompatibility, and being eco-friendly, and have improved PCE and stability by modifying both functional layers and interface. In this review, we discuss the roles of natural molecules on PSCs devices in terms of the perovskite active layer, interface, carrier transport layers (CTLs), and substrate. Finally, the summary and outlook for the future development of natural molecule-modified PSCs are also addressed.

Solution-processed perovskite wires are attractive candidates for photodetectors (PDs) due to their simple processibility as well as one-dimensional (1D) geometry with desirable charge carrier transport. However, the performance of the perovskite PDs is generally restricted by the charge carrier transport and extraction efficiency. Herein, we demonstrate that the charge transport and the consequent photodetection performance of MAPbI 3 perovskite wires can be effectively enhanced by incorporating nanocrystals (NCs) of GaAs—a semiconductor with high charge carrier mobility. Taking advantage of the pulsed laser irradiation technique, we successfully fabricate ligand-free GaAs NCs with a size of ∽7 nm and homogeneously embed them in MAPbI 3 perovskite wires through a simple solution-processed synthesis route. Compared with the pristine perovskite wires, the GaAs NCs modulated perovskite wires show improved charge carrier transport with the mobility rising from 1.13 to 3.67 cm 2 V −1 s −1 , and the resultant PD shows significant improvement in responsivity and detectivity. This study provides a new strategy for improving optoelectronic properties of halide perovskite materials and optimizing the device performance.

Colloidal quantum dots of CsPbBr 3 perovskites have been synthesized. The average size and polydispersity of nanocrystals were determined to be 8.3 nm and 16%, respectively. Thin films were made based on the obtained nanocrystals using drop-casting and spin-coating methods. The charge carrier transport process was studied using the technique of femtosecond laser pump–probe spectroscopy. An interpretation of the shift in the bleaching peak as a function of time is proposed. The mobility of charge carriers in films has been estimated using the Einstein–Smoluchowski equation.