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The metal stop laser drilling of GaN‐on‐GaN devices is demonstrated using a UV sub‐nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser‐induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal‐to‐noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through‐substrate electrode with a resistance of less than 5 mΩ on GaN‐on‐GaN high‐electron‐mobility transistor (HEMT) wafers is demonstrated. The fabrication of through‐substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN‐on‐GaN devices, including very thin GaN‐on‐GaN HEMTs. [ABSTRACT FROM AUTHOR]

With the arrival of the "von Neumann bottleneck," neuromorphic systems are receiving a lot of attention from scholars as an innovative technology by mimicking the massive parallelism and low‐power operation of the human brain. Herein, a floating‐gate‐like device constructed by the InSe/hBN/O2‐hBN van der Waals heterostructure, where the defective O2‐hBN plays the central role to trap charges, is proposed. This well‐designed device is proved to realize the synaptic functions under UV laser irradiation, such as short‐term plasticity (STP), long‐term plasticity (LTP), paired‐pulse facilitation (PPF), and long‐term potentiation/long‐term depression (LTP/LTD). Especially, the synaptic weight of excitatory postsynaptic current (EPSC) reaches as high as 104%, it reaches the highest standard of this kind of device in recent years, and remains above 300% synaptic weight after 200 s, thus successfully imitating the LTP in biological synapses. The key factors of LTP/LTD curves are overall excellent and can be optimized with input pulses: nonlinearity value can reach 3.32/2.35, and Gmax/Gmin above 10 is achieved. The InSe floating‐gate‐like device with O2‐hBN layer provides an alternative for better and more practical synaptic performances in the field of neuromorphic architectures based on 2D materials. [ABSTRACT FROM AUTHOR]

Micrometric foils of graphene oxide are prepared in the laboratory starting from water dispersed solution of graphene oxide at low concentration. Measurements on five physical properties have been performed in the foils of graphene oxide and reduced graphene oxide. The reduction is obtained thermally, using IR and UV laser irradiations and MeV helium ion beam irradiations at different fluence. The parameters such as the atomic composition, the mass density, the surface roughness, the wetting ability, and the electrical conductivity are investigated. This last parameter assumes different values for the pristine graphene oxide foils and for the reduced ones. Comparison of experimental measurements with the literature data and the results and discussion are presented. [ABSTRACT FROM AUTHOR]

Deep ultraviolet (UV) photodetectors have wide applications both in civil and military fields. Many materials have been explored to realize deep UV photodetection. Amorphous gallium oxide (a‐GaOx), as a member of transparent amorphous oxide semiconductors (TAOSs), has attracted a great deal of attention due to its ultrawide bandgap and scalable synthesis at room temperature. Plenty of researches have been focused on this topic in recent years. Herein, the latest progresses in the preparation methods of a‐GaOx using radio‐frequency sputtering, pulsed laser deposition, atomic layer deposition, and other deposition techniques are summarized. Dependence of the stoichiometry, crystallinity, optical, electrical, and morphological properties on different preparation parameters and doping/alloying elements is tentatively discussed, as well as those deep UV photodetectors based on a‐GaOx and related thin films. Finally, a short summary with further possible investigations is provided for a better understanding and development of a‐GaOx materials and photodetectors. [ABSTRACT FROM AUTHOR]

The objective of this article is to demonstrate a general approach to the problem of designing a novel laser diode. This involves first understanding prior work in this and related fields (literature survey), and then acquiring a thorough understanding of the relevant physics. This in turn enables the development and/or selection of appropriate models and tools for that problem followed by partitioning the problem into smaller solvable chunks. This involves identifying the key contributing factors affecting poor laser performance (sources of optical loss, poor injection efficiency, high thermal resistance, etc.), quantifying and ranking their relative importance, and finally finding solutions to these problems. The final step involves putting all these pieces back together to arrive at the final laser design. This step is challenging due to the strong coupling between electrical, optical, and thermal physics in a laser diode. Any design changes must be considered through all three lenses. Herein, this approach to laser design will be demonstrated in the context of a novel III–N‐based ultraviolet vertical‐cavity surface‐emitting laser diode (UV‐VCSEL). [ABSTRACT FROM AUTHOR]

Michael Kneissl, TU Berlin (Germany) Jürgen Christen, University of Magdeburg (Germany) B Conference Chairs b Axel Hoffmann, TU Berlin (Germany) Bo Monemar, Linköping University (Sweden) B Honorary Chairs b Tim Wernicke, TU Berlin (Germany) B Conference Secretary b Ulrich Schwarz, TU Chemnitz (Germany) B Local Chair b Åsa Haglund, Chalmers University of Technology (Sweden) Matteo Meneghini, University of Padova (Italy) B Guest Editors and Publication Chairs b Two tutorial speakers (Andreas Waag, TU Braunschweig) and Chris Van de Walle (UCSB) opened the workshop, by discussing GaN-based micro-LEDs and point defects, respectively. The workshop organizers express their gratitude to the plenary and invited speakers, rump session chairs, panelists, and short-course presenters for their exceptional contributions to an engaging workshop. [Extracted from the article]

Compared with GaN-based visible GaN/InGaN multiple-quantum-well laser diodes (LDs), near-ultraviolet LDs may suffer from a sever hole leakage due to the shallower quantum wells (QWs). Here, a 10 nm n-type AlGaN hole blocking layer (HBL) is proposed to put before the first quantum barrier layer and form a barrier on the valence band to prevent injected holes from leaking into the n-type region. Furthermore, the effect of Al composition of Al xGa1− xN HBL on LD performance is studied. Theoretical analysis is performed by using advanced device simulation. The simulation results show that lower threshold current and higher output power of LD can be obtained when Al composition of Al xGa1− xN HBL is 0.23. This result can be attributed to a dramatically reduced electron and hole leakage, and more stimulated recombination in QWs. [ABSTRACT FROM AUTHOR]

This work reports on the effect of ultraviolet (UV) laser irradiation on the structural, electrical, and optical properties of nickel oxide (NiO x) thin films, deposited by reactive sputtering of nickel in an oxygen containing atmosphere. It was found that the conduction type can be changed from p-type to n-type and the resistivity decreased as the number of laser pulses is increased and then increases again. The as-deposited films are polycrystalline, while laser irradiation renders the films amorphous. The observed transition from O-rich NiO x as-deposited films to Ni-rich laser-irradiated NiO x can be significant to electrochromic, resistive switching, and other applications. The band gap of the as-deposited and the laser irradiated NiO x films was obtained from spectroscopic ellipsometry measurements and was found to slightly increase upon laser irradiation. It is also observed that the surface roughness increases slightly. Aging effects or instabilities in the structure and composition of the films are also observed under normal conditions. [ABSTRACT FROM AUTHOR]

Abstractauthoren Nickel thin films were deposited on Ti6Al4V and surface treated with nanosecond pulse ultraviolet laser in ambient conditions using a fluence of 3.68 J cm−2. A twofold to threefold increase in contact angle was observed for water, ethylene glycol, and diiodomethane following laser treatment, with recorded contact angles for water in excess of 130°. No additional treatment was used to hydrophobize the surface. Three different micro- and nanometric levels of roughness were generated on the thin film surface, which can be related to the rastering parameters of the laser and to the increase in apparent contact angle. Melt droplets were identified as a main contribution to the nanometric roughness level, indicating that melting and melt ejection play an important role in surface nanostructuring. Micro- and nanopatterning obtained after UV laser treatment of nickel thin films, highlighting the different scales of the generated features. [ABSTRACT FROM AUTHOR]

AlGaN-based graded-index-separate-confinement-heterostructures (GRINSCHs) with Al0.65Ga0.35N/Al0.8Ga0.2N MQWs in their active region were grown by plasma-assisted MBE on (0001) 6H-SiC substrates. The MQWs were grown under excess Ga. Indium flux was used in addition in some of the samples in order to study the role of indium on the growth mode of such MQWs. Transmission electron microscopy (TEM) provides evidence that the bottom compositionally graded AlGaN layer in the GRINSCH structure may also be serving as a strain transition buffer layer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. X-ray diffraction (XRD) indicates that the interfaces in the MQWs grown in the presence of indium are sharper. However, photoluminescence (PL) studies indicate evidence of stimulated emission at relatively low threshold only in the sample grown without indium, which is attributed to deep band structure potential fluctuations in this sample. The presence of indium during growth led to more homogeneous AlGaN MQWs, which require higher excitation flux to produce population inversion. [ABSTRACT FROM AUTHOR]

Morphology, Luminescence, and Optical Properties of Tb- and Li-Codoped ZnO Elongated Nano- and Microstructures B ZnO Elongated Nano- and Microstructures b The sword-like structure depicted on the cover constitutes a resonant cavity (Fabry-Perot type) for the green emission induced by the UV laser. No light escapes from the structure except through the two symmetrical exit points located at the side edges. [Extracted from the article]

Furthermore, the sp SP 3 sp structure of the diamond transforms into the sp SP 2 sp graphite phase during the ultraviolet nanosecond laser micromachining. B Polycrystalline Diamond b In article number 2100450, Jianlei Cui and co-workers study the ablation threshold and phase transition of polycrystalline diamond under the irradiation of an ultraviolet nanosecond laser with a wavelength of 355 nm. [Extracted from the article]

Optically pumped deep-ultraviolet lasers operating at room temperature are demonstrated from heterostructures consisting of Al xGa1− xN/AlN grown on (0001) AlN substrate. The substantial reduction of the threading dislocation density by using a native AlN substrate over sapphire substrates is critical to the realization of the photo-pumped lasers. The threshold power density was 1.88 MW cm−2. The layers below the active region were Si-doped and had bottom waveguide and cladding layer n -type structures required for diode lasers, thus demonstrating the feasibility of deep UV lasing for the proposed structures on AlN substrates by current injection, provided that effective hole injection layers are included. [ABSTRACT FROM AUTHOR]