Conference Agenda

Semiconductor spintronics holds the potential for opto-spintronics that will allow integration of spin-based information processing and storage with photon-based information transfer. Unfortunately, progresses of semiconductor spintronics have during the last three decades been severely hampered by the failure to generate nearly fully spin-polarized charge carriers at and above room temperature (RT). Here, by exploring a new approach of defect-engineered remote spin filtering, we demonstrate that dilute-nitride III-V nanostructures based on coupled GaNAs and InAs quantum dots can be tailor-made for RT opto-spintronics - achieving the highest RT electron spin polarization (exceeding 90%) ever reported in any semiconductor by any approach! This is accompanied by an array of extraordinary spin functionality including spin filtering, spin amplification, dynamic nuclear spin polarization, non-linear spin dynamics and polarized spin-photon conversion, making this material system attractive for a range of potential spintronic and opto-spintronic applications exploiting the state-of-the-art GaAs technology platform, such as spin-LEDs, spin lasers, spin-polarized single-photon sources, spin-photon interfaces, spin qubits.

Transmission electron microscopy (TEM) was employed to investigate the micromorphological properties of subsurface lattice damage (SLD) in ground and rough polished InAs substrates. We show that the types and distributions of SLD defects in ground substrates and rough polished substrates are different obviously, which are more complex compared to those in other hard-brittle materials. Remarkably, the depth of SLD layer containing severely damaged regions, abnormal contrasts and moiré fringes in rough polished substrates, is three times deeper than that of SLD layer composed of dislocations, stacking faults and subsurface cracks in ground substrates. SLD in the rough polished substrate exhibits defect characteristics of lattice glide caused by the force applied during the polishing process.

GaAsBi nanowires (NWs) are promising materials for optoelectronic applications, e.g. as solid-state light emitters within the near-infrared spectral range. In this work, we employ photoluminescence (PL) and PL excitation spectroscopies to examine recombination processes in these novel materials and their dependence on growth conditions during the NW fabrication. We show that radiative recombination in GaAsBi-based NWs is dominated by excitons bound to Bi-related clusters. The formation of these clusters is affected by Bi beam equivalent pressure (BEP) during the growth so that larger Bi clusters, which introduce deep states within the bandgap, are formed under conditions of high Bi BEP.

A novel broadband p-n UV photodiode that integrates a n-type Si-doped k-Ga₂O₃ epitaxial film and a p-type NiO polycrystalline film is presented. The proposed device, based on the planar NiO/k-Ga₂O₃ p-n heterojunction, can work in self-powered mode for UV detection. The p-n photodiode exhibits fast response (<0.8 s), very good sensitivity to UV-C light, and appreciable response to UV-B and UV-A wavelengths.

In this work, a 7 nm ScAlN barrier GaN High Electron Mobility Transistor (HEMT) structure is grown on silicon (111) substrate by ammonia-source molecular beam epitaxy (NH3-MBE). On 75 nm T-shaped gate transistor, a saturated current density of 1.35 A/mm at a gate bias of 0V and a transconductance peak higher to 280 mS/mm are reached. Transition frequencies fT/fmax of 82 / 112 GHz are reported. At VDS = 8 V, continuous-wave (CW) output power density of 1 W/mm is achieved at 10 GHz with 16 % associated Power-Added Efficiency (PAE) and a linear power gain of 10 dB. These preliminary results demonstrate the potential of ScAlN/GaN-based HEMTs on low-cost silicon substrates.

Recently, Ga₂O₃-based photodetectors have attracted much interest due to their potential applications in space exploration, environmental monitoring, and security systems. Self-powered and efficient devices of this kind will enable significant advancements for the next generation of photodetection applications. In this work, we present a selective UV-C photodiode prototype based on planar p-n NiO/β-Ga₂O₃ heterojunction with circular geometry. β-Ga₂O₃ epilayers are grown using metal-organic vapor phase epitaxy (MOVPE), while the NiO polycrystalline film is deposited by sputtering at room temperature. The photodiode operates in self-powered mode and exhibits high responsivity and selectivity to UV-C light, with fast response and recovery times of 0.28 s and 0.18 s, respectively. Notably, no persistent photocurrent is observed during the on-off illumination cycles; the photocurrent rapidly returns to baseline after each UV-C illumination. This prototype shows great potential for high-performance UV-C detection applications.

Gallium oxynitride thin films were deposited by reactive radio frequency sputtering. A high throughput combinatorial material synthesis method was used to study a wide range of compositions. Structural (X-ray diffraction) and optical (spectroscopic ellipsometry) characterizations were performed to investigate their dependence on the chemical composition of the layers. A correlation between the optical bandgap and the oxygen concentration of the films was found.

The performance and reliability of GaN high-electron-mobility transistors (HEMTs) are strongly influenced by self-heating effects. Electrothermal Monte Carlo (MC) simulations provide accurate modelling but require substantial computational resources. This work introduces a hybrid AI-thermal model that integrates MC-generated training data with an artificial neural network (ANN) to predict self-heating effects efficiently. The ANN, coupled with thermal models, iteratively estimates current density and lattice temperature (T_latt). Compared to full electrothermal MC simulations, the proposed model maintains high accuracy while drastically reducing computational costs, providing a fast and effective tool for GaN HEMT optimization.

This study investigates the structural and compositional transformation of gallium selenide (GaSe) into gallium oxide (Ga₂O₃) via thermal oxidation, a process that enhances environmental stability and widens the bandgap beyond 3 eV, which are key attributes of ultraviolet photodetectors and insulating layers in electronic applications. Thin GaSe layers were grown on sapphire substrates using molecular beam epitaxy (MBE) and subjected to controlled thermal annealing in an oxygen-rich atmosphere at temperatures ranging from 400 to 900 °C. STEM-related techniques were employed to analyse the crystallographic structure and chemical composition. The results indicate a full transformation of GaSe into β-Ga₂O₃ at temperatures exceeding 600 °C, as evidenced by the [Ga]:[O] ratio of 2:3 and the disappearance of elemental selenium. The oxide layer exhibits high crystallinity with nanoscale voids, which compensates the expected lattice contraction during oxidation. These findings contribute to the fundamental understanding of GaSe oxidation processes and highlight the potential of thermally grown Ga₂O₃ layers in optoelectronic applications.

Gallium Nitride (GaN) transistors have become a key technology in high-frequency and high-power applications. N++GaN/InAlN/GaN heterostructure is a promising platform for realizing enhancement (E-mode) and depletion (D-mode) mode devices on the same wafer. In this work we explore digital etching as a precise method for tuning n++GaN cap thickness in D-mode transistors. By implementing a cyclic oxidation and etching process, we achieve controlled treatment of the cap surface, enabling transistor operation without compromising high current or introducing current collapse.