Feras AlQatari’s research while affiliated with King Abdullah University of Science and Technology and other places

This work investigates the impact of the Silicon (Si) loading effect induced by Deep Reactive Ion Etching (DRIE) on UV-nanoimprint lithography (NIL) patterning of nanofeatures. Silicon was chosen for its known stiffness, ability to achieve very small pattern sizes down to 6 nm with a high aspect ratio, and cost-effectiveness. However, creating a stamp for nanoimprint lithography with complex patterns presents challenges due to the silicon loading problem. Silicon molds, patterned with metasurface features of varying widths from 270 nm to 60 nm, were analyzed using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and Atomic Force Microscopy (AFM). The Si loading effect, characterized by variations in feature depth, showed that smaller features etch more slowly due to difficulties in etchant penetration and byproduct diffusion. Silicon's excellent etching properties and ability to maintain feature integrity at sub-10 nm scales make it an ideal choice for NIL despite these challenges. Our results are crucial for advancing NIL in commercial applications, ensuring high-quality pattern transfer for diverse nanostructures. Figure 4. Optical setup used to characterize the optical behavior of the NIL-fabricated metalens. The setup includes a laser source, a series of lenses, and a camera. Images of the focal point were obtained and analyzed to study the intensity distribution. Each image corresponds to a different lens, highlighting the focal point characteristics. METALENS DESIGN METHOD-10-5 0 5 10 0.0 0.5 1.0 Normalized Intensity (a.u.) x (µm) 0°0 .460mm Metalens FDTD Results Unit-Cell RESULTS AND DISCUSSION [1]. Baracu, A., et al; Silicon Metalens Fabrication from Electron Beam to UV-Nanoimprint Lithography. Nanomaterials, 11(9), pp.2329-2329. [2].. Alnakhli, Z., et al., UV-assisted nanoimprint lithography: the impact of the loading effect in silicon on nanoscale patterns of metalens. Nanoscale Advances, 2024. 6(11): p. 2954-2967. Figure 3. Effects of silicon loading on metalens fabrication. The silicon master mold, processed by Bosch-DRIE, shows that minimal silicon loading ensures successful metalens creation. AFM characterization and precise removal of the photoresist residual layer are critical to the process. Significant silicon loading and improper residual layer removal hinder successful fabrication. VS We utilized UV-assisted NIL to fabricate metalenses, beginning with the creation of a silicon master mold. The process included: Master Mold Creation: Patterning of silicon with metasurface features using DRIE. Stamp Mold Preparation: Using a glass plate and prepolymer mixture cured with UV light to form the stamp mold. Our study revealed that the Si loading effect significantly impacts the etching uniformity in DRIE. Specifically, areas with higher silicon loading exhibited slower etch rates and increased byproduct accumulation, leading to variations in feature depth. This finding emphasizes the need for optimized etching parameters to achieve uniform nanostructures. Optimizing DRIE parameters for silicon master molds is crucial for achieving high-quality NIL patterning. Our findings provide valuable insights into controlling the Si loading effect, paving the way for advanced nanofabrication techniques in commercial applications. REFERENCES

This work studies the impact of the silicon (Si) loading effect induced by deep reactive ion etching (DRIE) of silicon master molds on the UV-nanoimprint lithography (NIL) patterning of nanofeatures. The silicon molds were patterned with metasurface features with widths varying from 270 to 60 nm. This effect was studied by focus ion beam scanning electron microscopy (FIB-SEM) and atomic force microscopy (AFM). The Si loading etching effect is characterized by the variation of pattern feature depth concerning feature sizes because smaller features tend to etch more slowly than larger ones due to etchants being more difficult to pass through the smaller hole and byproducts being harder to diffuse out too. Thus, the NIL results obtained from the Si master mold contain different pattern geometries concerning pattern quality and residual photoresist layer thickness. The obtained results are pivotal for NIL for fabricating devices with various geometrical nanostructures as the research field moves towards commercial applications.

The polarization-induced quantum confined Stark effect has been recognized as a significant factor contributing to the Internal Quantum Efficiency (IQE) droop in light-emitting diodes (LEDs). This study focuses on the design of LEDs by investigating the InAlN/AlGaN interface. By incorporating InAlN quantum wells, a polarization-matched (PM) multi-quantum well (MQW) LED architecture was developed. While the flat conduction and valence bands on PM MQWs indicate an improved recombination rate, it is crucial to examine the impact on IQE, considering carrier confinement and injection efficiency influenced by the band offsets. This paper presents a numerical analysis comparing two LEDs emitting at 245 and 275 nm, respectively. The results demonstrate that the PM LED operating at 275 nm exhibits enhanced performance, benefiting from high probability density overlap. Conversely, the PM LED emitting at 245 nm demonstrates poor confinement, resulting in an overall low performance, regardless of polarization matching.

The electronic structure of B 0.097 Ga 0.903 N was determined by examining its bandgap and valence band offset (VBO) in detail. The BGaN sample was grown using a horizontal reactor metalorganic chemical vapor deposition. For bandgap determination, three different techniques were utilized yielding similar results, which are: UV-Vis spectroscopy, Schottky photodiodes, and electron energy-loss spectroscopy. The bandgap was determined to be ~3.55 eV. For measuring the VBO, the valence edges and the core levels of Al 2s and Ga 2p were measured using x-ray photoelectron spectroscopy (XPS). The valence edges were then fitted and processed along with the core levels using the standard Kraut method for VBO determination with AlN. The BGaN/AlN alignment was found to be -1.1 ± 0.1 eV. Due to core level interference between GaN and BGaN, the Kraut method fails to provide precise VBO for this heterojunction. Therefore, a different technique is devised to analyze the measured XPS data which utilizes the alignment of the Fermi levels of the BGaN and GaN layers when in contact. Statistical analysis was used to determine the BGaN/GaN alignment with decent precision. The value was found to be -0.3 ± 0.1 eV.

In this Letter, we report on a monolithically integrated β-Ga 2 O 3 NMOS inverter integrated circuit (IC) based on heteroepitaxial enhancement mode (E-mode) β-Ga 2 O 3 metal-oxide-semiconductor field-effect transistors on low-cost sapphire substrates. A gate recess technique was employed to deplete the channel for E-mode operation. The E-mode devices showed an on-off ratio of ∼10 ⁵ with a threshold voltage of 3 V. In comparison, control devices without the gate recess exhibited a depletion mode (D-mode) with a threshold voltage of [Formula: see text]3.8 V. Furthermore, depletion-load NMOS inverter ICs were fabricated by monolithically integrating D- and E-mode transistors on the same substrate. These NMOS ICs demonstrated inverter logic operation with a voltage gain of 2.5 at V DD = 9 V, comparable with recent GaN and other wide-bandgap semiconductor-based inverters. This work lays the foundation for heteroepitaxial low-cost and scalable β-Ga 2 O 3 ICs for monolithic integration with (ultra)wide bandgap Ga 2 O 3 power devices.

Piezoelectric Sensor In article number 2212538, Jae‐Hyun Ryou and co‐workers develop a highly sensitive and mechanically flexible piezoelectric sensor using an ultrawide‐bandgap single‐crystalline AlN semiconductor thin film that can operate at higher than 900 °C. The operation temperature is believed to be amongst the highest for pressure sensors, and the inherent properties of AlN indicate that this approach offers a new solution for sensing in extreme environments often faced in current and next‐generation energy, transportation, and defense applications.

Extreme environments are often faced in energy, transportation, aerospace, and defense applications and pose a technical challenge in sensing. Piezoelectric sensor based on single‐crystalline AlN transducers is developed to address this challenge. The pressure sensor shows high sensitivities of 0.4–0.5 mV per psi up to 900 °C and output voltages from 73.3 to 143.2 mV for input gas pressure range of 50 to 200 psi at 800 °C. The sensitivity and output voltage also exhibit the dependence on temperature due to two origins. A decrease in elastic modulus (Young's modulus) of the diaphragm slightly enhances the sensitivity and the generation of free carriers degrades the voltage output beyond 800 °C, which also matches with theoretical estimation. The performance characteristics of the sensor are also compared with polycrystalline AlN and single‐crystalline GaN thin films to investigate the importance of single crystallinity on the piezoelectric effect and bandgap energy‐related free carrier generation in piezoelectric devices for high‐temperature operation. The operation of the sensor at 900 °C is amongst the highest for pressure sensors and the inherent properties of AlN including chemical and thermal stability and radiation resistance indicate this approach offers a new solution for sensing in extreme environments.

Al2O3 is a broadly employed dielectric and significant interfacial charges occur at Al2O3/semiconductor interfaces. However, the charge origin is often unclear that severely impacts device engineering and design. Al2O3/Si and Al2O3/GaN are two of the most common heterogeneous heterostructures (H2s) for many crucial devices including GaN transistors and Si solar cells. While negative charges are extensively observed in Al2O3/Si, positive charges exist in Al2O3/GaN, both of which are not well understood. In this study, we performed in-depth interfacial studies of the Al2O3/Si and Al2O3/GaN H2s to clarify the origin of the interfacial charges. Stoichiometry deviations were found at the interfaces of the two H2s where Al surpasses O for Al2O3/GaN, whereas O dominates at the Al2O3/Si interface. Therefore, we propose that the different interfacial charges are caused by nonstoichiometry atomic ratios of Al2O3 at the interface. The study indicates the important role of the semiconductor surface on the device performance, provide a deep understanding on the origin of interfacial charges at the insulator-semiconductor interfaces.