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We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h under atmospheric conditions. This was accomplished by characterizing AlGaN/AlN/GaN micro-Hall sensors, with and without contacts, and before and after being placed under different thermal aging times. Observed electrical performance was correlated with the micro-structural evolution of AlGaN/AlN/GaN Hall sensor heterostructures. Results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h aging at 200 °C without any significant degradation of (i) Hall sensitivity, (ii) two-dimensional electron gas, and (iii) Ohmic contacts. However, there was a small change in sheet density and mobility, which is due to a decrease in polarization, resulting from local inhomogeneous strain relief at the barrier layer. During the early stage of thermal aging, a decrease in contact resistance was also observed and attributed to (i) out-diffusion of "Ga" at the vicinity of the contact interface, and (ii) a reduction in oxygen concentration and formation of Al–Ti intermediate alloy at the GaN/Ti interface, resulting in a reduced barrier and enhanced electron transport at the contacts. However, despite these small changes, results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h thermal aging at 200 °C. [ABSTRACT FROM AUTHOR]

This research provides a flexible approach to manipulate formation of InGaAs nanostructures on the GaAs (100) surface by varying arsenic (As4) beam equivalent pressure (BEP). By selecting the As4/(In+Ga) BEP ratio to be 4, 8, 20, 50 and 100, we were able to obtain different quantum structures from quantum well (QW) to quantum dots (QDs), then to spatially ordered quantum dot chains (QD-chains), and finally to quantum wires (QWRs), respectively. This transformation of nanostructures was explained by anisotropic surface diffusion coupled with the strain relieving Stranski–Krastanov growth mode, while the anisotropy was modulated by increasing As4 flux and subsequently enhanced by multilayer-stacking growth with a suitable spacer thickness. Photoluminescence characteristics show correlation to the nanostructure morphology for each sample. In particular, the formation of QD-chains and QWRs results in anisotropic features that offer potential device applications. [ABSTRACT FROM AUTHOR]

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III–V materials. In parallel with developing active devices for photonics integration applications, in this work, silicon nitride optical waveguides on a sapphire substrate were analyzed using the commercial software Comsol Multiphysics in a spectral window of 800~2400 nm, covering the operating wavelengths of III–V lasers, which could be monolithically or hybridly integrated on the same substrate. A high confinement factor of ~90% near the single-mode limit was obtained, and a low bending loss of ~0.01 dB was effectively achieved with the bending radius reaching 90 μm, 70 μm, and 40 μm for wavelengths of 2000 nm, 1550 nm, and 850 nm, respectively. Furthermore, the use of a pedestal structure or a SiO2 bottom cladding layer has shown potential to further reduce bending losses. The introduction of a SiO2 bottom cladding layer effectively eliminates the influence of the substrate's larger refractive index, resulting in further improvement in waveguide performance. The platform enables tightly built waveguides and small bending radii with high field confinement and low propagation losses, showcasing silicon nitride waveguides on sapphire as promising passive components for the development of high-performance and cost-effective PICs. [ABSTRACT FROM AUTHOR]

We report on the growth of high-quality GaAs semiconductor materials on an AlAs/sapphire substrate by molecular beam epitaxy. The growth of GaAs on sapphire centers on a new single-step growth technique that produces higher-quality material than a previously reported multi-step growth method. Omega-2theta scans confirmed the GaAs (111) orientation. Samples grown at 700 °C displayed the highest crystal quality with minimal defects and strain, evidenced by narrow FWHM values of the rocking curve. By varying the As/Ga flux ratio and the growth temperature, we significantly improved the quality of the GaAs layer on sapphire, as compared to that obtained in multi-step studies. Photoluminescence measurements at room temperature and 77 K further support these findings. This study underscores the critical role of the As/Ga flux ratio and growth temperature in optimizing GaAs epitaxial growth on sapphire. [ABSTRACT FROM AUTHOR]

The study aimed to investigate the underlying physics limiting the temperature stability and performance of non-surface passivated Al0.34Ga0.66N/GaN Hall effect sensors, including contacts, under atmospheric conditions. The results obtained from analyzing the microstructural evolution in the Al0.34Ga0.66N/GaN Hall sensor heterostructure were found to correlate with the electrical performance of the Hall effect sensor. High-resolution x-ray photoelectron spectroscopy studies revealed the signature of surface oxidation in the GaN cap layer, as well as a slight out-diffusion of "Al" from the AlGaN barrier layer. To prevent the formation of a bumpy surface morphology at the Ohmic contact, we investigated the impact of "Pt" top Ohmic contacts. The application of a top "Pt" contact stack resulted in a smooth Ohmic contact surface and provided evidence that the bumpy surface morphology in Au-based Ohmic contacts is due to the formation of an Al-Au viscous alloy during rapid thermal annealing. In the early stages of thermal aging, the small drop in contact resistivity stabilized with subsequent thermal aging past the initial 550 h at 200 °C. The outcome is that the Al0.34Ga0.66N/GaN Hall effect sensors, even without surface passivation, exhibited a stable response to applied magnetic fields with no sign of significant degradation after 2800 h of thermal aging at 200 °C under atmospheric conditions. This observed stability in the Hall sensor without surface passivation can be attributed to a self-imposed surface oxidation of the cap layer during the early stages of aging, which serves as a protective layer for the device during subsequent extended periods of thermal aging at 200 °C. [ABSTRACT FROM AUTHOR]

The development of all-group IV GeSn materials on Si substrates is of interest for monolithic midwave infrared (MWIR) silicon photonics. Despite their great potential, the growth of high crystalline quality materials is still challenging. The conventional growth of GeSn films on Si displays high densities of dislocations and, hence, large dark currents. We have examined a state-of-the-art lithographically defined aspect ratio trapping (ART) growth approach for threading dislocations (TDs) filtering in GeSn and demonstrated the selective growth in the holes embedded in the SiO2/Si(001) template. While an exceptionally low density of TDs was confirmed by transmission electron microscopy imaging, we find that Sn incorporation is strongly suppressed in the ART-grown structures. Nonetheless, these results provide a solid basis for further efforts to enhance the Sn fraction of the GeSn ART growth. [ABSTRACT FROM AUTHOR]

SiC is an indirect bandgap semiconductor with material properties ideal for power electronics but not so much as an optical emitter. Meanwhile, gallium arsenide (GaAs) is a material known for high-performance optical devices due to its direct bandgap and carrier lifetime. Integrating GaAs with silicon carbide (SiC) can result in the best of both materials. However, integrating the two presents a significant challenge due to the large lattice mismatch between the two materials. In this paper, we investigate the growth of high-quality GaAs directly on 4H-SiC and on AlAs/4H-SiC substrates. The thin films were characterized using key techniques for structural and optical analyses, such as x-ray diffraction, atomic force microscopy, and photoluminescence (PL) spectroscopy. The 3D-island nature of growth of GaAs directly on SiC results in weak in-plane correlation with the substrate but high photoluminescence. This was demonstrated with an observed PL intensity comparable to the PL observed from a GaAs substrate with a similar buffer layer. Introduction of a thin AlAs nucleation layer results in improved wetting of the substrate, better in-plane correlation with substrate, and overall improved crystalline quality and is now under further study. [ABSTRACT FROM AUTHOR]

High-quality monolithic Ge-on-Si is sought for CMOS-compatible optoelectronic devices. We examine the structural characteristics of Ge-on-Si grown by the aspect ratio trapping (ART) method on a SiO2/Si(001) template in pre-patterned holes. Transmission electron microscopy and surface topography analysis revealed high-quality Ge islands overgrown from the ART holes in SiO2. The superior crystal quality of Ge ART growth was also confirmed by comparing x-ray diffraction (XRD) data of Ge ART and Ge planar epilayer samples. The XRD and micro-Raman data additionally show a small residual strain in the islands which vanishes by reducing the hole diameter from 280 nm to 180 nm, while leading to only a minor increase in the crystallographic inclinations of the Ge islands from 0.34 deg to 0.54 deg. With finite element method simulations, we find that the small residual strain in Ge originates during the cool-down from growth to room temperature because of thermal expansion coefficient mismatch between Ge and SiO2. A tensile force develops along the [001] axis of the Ge pillar whose faster shrinkage to the room temperature volume is restricted by the oversized surface island. [ABSTRACT FROM AUTHOR]

This study provides psychometric data for the Scholastic Inquiry Observation instrument and 6 years of research data from an inquiry-based professional training program. The rating instrument provides a resource for measuring 16 inquiry-related learning activities based on level of inquiry implementation and level of active student engagement. Observational data at the item level can be useful for inquiry-based professional development programs. Four scale score options are available for inquiry summarization (Inquiry Implementation for Hypothesis Usage; Implementation of Inquiry Communication; Student Engagement in Hypothesis Usage; Student Engagement in Inquiry Communication) and two scales measuring Student Interest and Mastery of Objectives. Comparisons of the types of inquiry most commonly used and those with the highest levels of active participation by middle school students in science and math classrooms are provided.

Ge1−xSnx growth on a new sapphire platform has been demonstrated. This involved the growth of GeSn on Ge/GaAs layers using the algorithm developed. The resultant growths of Ge on GaAs/AlAs/sapphire and Ge1−xSnx on Ge/GaAs/AlAs/sapphire were investigated by in situ and ex situ characterization techniques to ascertain the surface morphology, crystal structure, and quality. The growth mode of Ge on GaAs was predominantly two-dimensional (2D), which signifies a layer-by-layer deposition, contributing to enhanced crystal quality in the Ge/GaAs system. The growth of Ge1−xSnx with 10% Sn on a graded profile for 30 min shows uniform composition and a strong peak on the reciprocal space map (RSM). On the other hand, the partially relaxed growth of the alloy on RSM was established. [ABSTRACT FROM AUTHOR]