Epitaxial Growth of MgxCa1-xO on GaN by Atomic Layer Deposition

Atomic Layer Deposition of Metal Oxides and Chalcogenides for High Performance Transistors

Atomic layer deposition (ALD) is a deposition technique well-suited to produce high-quality thin film materials at the nanoscale for applications in transistors. This review comprehensively describes the latest developments in ALD of metal oxides (MOs) and chalcogenides with tunable bandgaps, compositions, and nanostructures for the fabrication of high-performance field-effect transistors. By ALD various n-type and p-type MOs, including binary and multinary semiconductors, can be deposited and applied as channel materials, transparent electrodes, or electrode interlayers for improving charge-transport and switching properties of transistors. On the other hand, MO insulators by ALD are applied as dielectrics or protecting/encapsulating layers for enhancing device performance and stability. Metal chalcogenide semiconductors and their heterostructures made by ALD have shown great promise as novel building blocks to fabricate single channel or heterojunction materials in transistors. By correlating the device performance to the structural and chemical properties of the ALD materials, clear structure-property relations can be proposed, which can help to design better-performing transistors. Finally, a brief concluding remark on these ALD materials and devices is presented, with insights into upcoming opportunities and challenges for future electronics and integrated applications.

Partially Crystallized Ultrathin Interfaces between GaN and SiNx Grown by Low-Pressure Chemical Vapor Deposition and Interface Editing

The formation mechanism of the partially crystallized ultrathin layer at the interface between GaN and SiN_x grown by low-pressure chemical vapor deposition was analyzed based on the chemical components of reactants and products detected by high-resolution sputter depth profile analysis by X-ray photoelectron spectroscopy. A reasonable mass action equation for the formation of Si₂N₂O was proposed from the feasibility analysis of the Gibbs free energy changes of the reaction. The high-energy-activated Ga₂O on the surface likely assists in the synthesis of the crystallized components. A well-defined 1ML θ-Ga₂O₃ transition interface was inserted into Si₂N₂O/GaN pure interface supercell slabs to edit the unsaturated state of the bonds. Low-density states can be achieved when the effective charges of the unsaturated atoms are adjusted to a certain interval.

From the source: student-centred guest lecturing in a chemical crystallography class

Guest lecturing is an underutilized teaching strategy that provides depth and richness in college-level chemistry courses. The authors have found that student-centred guest lecturing that combines themed guest presentations, hands-on workshops (whenever possible) and small group conversations has yielded tremendous benefits. As a result, students have developed a lasting interest in chemical crystallography and have employed advanced experiments in their own research. The authors report on their experience in planning student-centred guest lecturing, advise on best practices, and demonstrate the long lasting positive impact on student learning and engagement.

New insights towards strikingly improved room temperature ethanol sensing properties of p-type Ce-doped SnO2 sensors

In this article, room temperature ethanol sensing behavior of p-type Ce doped SnO₂ nanostructures are investigated successfully. Interestingly, it is examined that the abnormal n to p-type transition behavior is caused by Ce doping in SnO₂ lattice. In p-type Ce doped SnO₂, Ce ion substituting the Sn is in favor of generating excess holes as oxygen vacancies, which is associated with the improved sensing performance. Although, p-type SnO₂ is one of the important materials for practical applications, it is less studied as compared to n-type SnO₂. Pure and Ce doped SnO₂ nanostructures were successfully synthesized by chemical co-precipitation method. The structure, surface morphology, unpaired electrons (such as free radicals), and chemical composition of obtained nanoparticles were studied by various kinds of characterization techniques. The 9% Ce doped SnO₂ sensors exhibit maximum sensor response of ~382 for 400 ppm of ethanol exposure with fast response time of ~5 to 25 sec respectively. Moreover, it is quite interesting that such enhancement of ethanol sensing is unveiled at room temperature, which plays a key role in the quest for better ethanol sensors. These remarkably improved sensing results are attributed to uniformly distributed nanoparticles, lattice strain, complex defect chemistry and presence of large number of unpaired electrons on the surface.

Atomic-Layer Deposition of Single-Crystalline BeO Epitaxially Grown on GaN Substrates

We have grown a single-crystal beryllium oxide (BeO) thin film on a gallium nitride (GaN) substrate by atomic-layer deposition (ALD) for the first time. BeO has a higher thermal conductivity, bandgap energy, and dielectric constant than SiO₂. As an electrical insulator, diamond is the only material on earth whose thermal conductivity exceeds that of BeO. Despite these advantages, there is no chemical-vapor-deposition technique for BeO-thin-film deposition, and thus, it is not used in nanoscale-semiconductor-device processing. In this study, the BeO thin films grown on a GaN substrate with a single crystal showed excellent interface and thermal stability. Transmission electron microscopy showed clear diffraction patterns, and the Raman shifts associated with soft phonon modes verified the high thermal conductivity. The X-ray scan confirmed the out-of-plane single-crystal growth direction and the in-plane, 6-fold, symmetrical wurtzite structure. Single-crystalline BeO was grown on GaN despite the large lattice mismatch, which suggested a model that accommodated the strain of hexagonal-on-hexagonal epitaxy with 5/6 and 6/7 domain matching. BeO has a good dielectric constant and good thermal conductivity, bandgap energy, and single-crystal characteristics, so it is suitable for the gate dielectric of power semiconductor devices. The capacitance-voltage (C-V) results of BeO on a GaN-metal-oxide semiconductor exhibited low frequency dispersion, hysteresis, and interface-defect density.