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Abstract Objective.This paper introduces a novel PET imaging methodology called 3-dimensional positron imaging (3Dπ), which integrates total-body coverage, time-of-flight (TOF) technology, ultra-low dose imaging capabilities, and ultra-fast readout electronics inspired by emerging technology from the DarkSide collaboration.Approach.The study evaluates the performance of 3Dπusing Monte Carlo simulations based on NEMA NU 2-2018 protocols. The methodology employs a homogenous, monolithic scintillator composed of liquid argon (LAr) doped with xenon (Xe) with silicon photomultipliers (SiPMs) operating at cryogenic temperatures.Main results.Substantial improvements in system performance are observed, with the 3Dπsystem achieving a noise equivalent count rate of 3.2 Mcps at 17.3 kBq ml⁻¹, continuing to increase up to 4.3 Mcps at 40 kBq ml⁻¹. Spatial resolution measurements show an average FWHM of 2.7 mm across both axial positions. The system exhibits superior sensitivity, with values reaching 373 kcps MBq⁻¹with a line source at the center of the field of view. Additionally, 3Dπachieves a TOF resolution of 151 ps at 5.3 kBq ml⁻¹, highlighting its potential to produce high-quality images with reduced noise levels.Significance.The study underscores the potential of 3Dπin improving PET imaging performance, offering the potential for shorter scan times and reduced radiation exposure for patients. The Xe-doped LAr offers advantages such as fast scintillation, enhanced light yield, and cost-effectiveness. Future research will focus on optimizing system geometry and further refining reconstruction algorithms to exploit the strengths of 3Dπfor clinical applications. 

An in situ metal-organic chemical vapor phase epitaxy is used to grow a complete AlGaN/GaN metal oxide semiconductor heterojunction field effect transistor (MOSHFET) structure, gated by a gallium oxide (Ga2O3) layer; we observed reduction in the interfacial trap density compared to its version wherein the Ga2O3 was grown ex situ, after breaking the vacuum, all else being the same. A remarkable decrease in the interfacial charge density for in situ MOSHFET structures in the range of 70%–88% for 10–30 nm oxide layer thickness and improvements in other electrical parameters required for high-performing devices were observed. 

We demonstrated a metal-organic chemical vapor deposition (MOCVD) of smooth, thick, and monoclinic phase-pure gallium oxide (Ga2O3) on c-plane sapphire using silicon-oxygen bonding (SiOx) as a phase stabilizer. The corundum (α), monoclinic (β), and orthorhombic (ε) phases of Ga2O3 with a bandgap in the 4.4 – 5.1 eV range, are promising materials for power semiconductor devices and deep ultraviolet (UV) solar-blind photodetectors. The MOCVD systems are extensively used for homoepitaxial growth of β-Ga2O3 on (001), (100), (010), and (¯2 01) β-Ga2O3 substrates. These substrates are rare/expensive and have very low thermal conductivity; thus, are not suitable for high-power semiconductor devices. The c-plane sapphire is typically used as a substrate for high-power devices. The β-Ga2O3 grows in the (¯2 01) direction on sapphire. In this direction, the presence of high-density oxygen dangling bonds, frequent stacking faults, twinning, and other phases and planes impede the heteroepitaxy of thick β-Ga2O3. Previously phase stabilizations with SiOx have been reported for tetragonal and monoclinic hafnia. We were able to grow ~580nm thick β-Ga2O3 on sapphire by MOCVD at 750 oC through phase stabilization using silane. The samples grown with silane have a reduction in the surface roughness and resistivity from 10.7 nm to 4.4 nm and from 371.75 Ω.cm to 135.64 Ω.cm, respectively. These samples show a pure-monoclinic phase determined by x-ray diffraction (XRD); have tensile strain determined by Raman strain mapping. These results show that a thick, phase-pure -Ga2O3 can be grown on c-plane sapphire which can be suitable for creating power devices with better thermal management. 

We report the gate leakage current and threshold voltage characteristics of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) with metal-organic chemical vapor deposition (MOCVD) grown β-Ga2O3 as a gate dielectric for the first time. In this study, GaN channel HFET and β-Ga2O3 passivated metal-oxide-semiconductor-HFET (MOS-HFET) structures were grown in MOCVD using N2 as carrier gas on a sapphire substrate. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the structural properties and surface morphology of the heterostructure. The electrical properties were analyzed using van der Pauw, Hall, and the mercury probe capacitance-voltage (C-V) measurement systems. The 2-dimensional electron gas (2DEG) carrier density for the heterostructure was found to be in the order of ~1013 cm-2. The threshold voltage shifted more towards the negative side for the MOSHFET. The high-low (Hi-Lo) frequency-based C-V method was used to calculate the interface charge density for the oxide-AlGaN interface and was found to be in the order of ~1012 cm2eV-1. A remarkable reduction in leakage current from 2.33×10-2 A/cm2 for HFET to 1.03×10-8 A/cm2 for MOSHFET was observed demonstrating the viability of MOCVD-grown Ga2O3 as a gate dielectric. 

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (2¯01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices. 

We report a comparative spectroscopic study on the thin films of epitaxial aluminum nitride (AlN) on basal plane sapphire (Al2O3) substrates grown in hydrogen (H2) and nitrogen (N2) gas reaction environments. AlN films of similar thicknesses (~3.0 µm) were grown by metal-organic chemical vapor deposition (MOCVD) for comparison. The impact of the gas environment on the AlN epilayers was characterized using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS), secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The study showed that AlN layers grown in a N2 environment have 50% less stress (~0.5 GPa) and similar total dislocation densities (~109/cm2) as compared to the films grown in a H2 environment. On the other hand, AlN films grown in a H2 gas environment have about 33% lesser carbon and 41% lesser oxygen impurities than films grown in a N2 growth environment. The possible mechanisms that influenced the structural quality and impurity incorporation for two different gas environments to grow AlN epilayers in the MOCVD system on sapphire substrates were discussed. 

The growth of monoclinic phase‐pure gallium oxide (β‐Ga₂O₃) layers by metal–organic chemical vapor deposition on c‐plane sapphire and aluminum nitride (AlN) templates using silicon‐oxygen bonding (SiO_x) as a phase stabilizer is reported. The β‐Ga₂O₃layers are grown using triethylgallium, oxygen, and silane for gallium, oxygen, and silicon precursors, respectively, at 700 °C, with and without silane flow in the process. The samples grown on sapphire with SiO_xphase stabilization show a notable change from samples without phase stabilization in the roughness and resistivity, from 16.2 to 4.2 nm and from 85.82 to 135.64 Ω cm, respectively. X‐ray diffraction reveals a pure‐monoclinic phase, and Raman spatial mapping exhibits higher tensile strain in the films in the presence of SiO_x. The β‐Ga₂O₃layers grown on an AlN template, using the same processes as for sapphire, show an excellent epitaxial relationship between β‐Ga₂O₃and AlN and have a significant change in β‐Ga₂O₃surface morphology.