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High ScN fraction ScxAl1−xN has promise in important application areas including wide bandwidth RF resonators and filters, and ferroelectric devices such as non-volatile memory, but demands high crystal quality. In this work, the role of the nucleation layer (NL), ScxAl1−xN growth temperature, and strain management to preserve the wurtzite crystal structure are investigated to maximize both acoustoelectric and ferroelectric material properties for high ScN fraction ScxAl1−xN grown on SiC substrates. A 5 nm AlN nucleation layer reduces the x-ray diffraction 0002 reflection full width at half maximum (FWHM) for a Sc0.32Al0.68N film by almost a factor of 2, and reducing the growth temperature to 430 °C enables a Sc0.40Al0.60N film with a FWHM of 4100 arcsec (1.1°) while being only 150 nm thick. Grading the initial ScxAl1−xN layer from x = 0.32 to 0.40 suppresses the formation of rock-salt grain nucleation at the Sc0.40Al0.60N lower interface and reduces the anomalously oriented grain density by an order of magnitude. Increasing the total ScxAl1−xN growth thickness to 500 nm produces an average x = 0.39 ScxAl1−xN layer with a FWHM of 3190 arcsec (0.89°) and an anomalously oriented grain areal fill factor of 1.0%. These methods enable the lowest heteroepitaxial ScxAl1−xN FWHM reported for x ∼ 0.4, with layer thicknesses and defect densities appropriate for high frequency (>10 GHz) filter applications. [ABSTRACT FROM AUTHOR]

Heterogeneous integration of functional oxides with ultra-wide bandgap (UWBG) semiconductors is desired for the realization of novel hybrid systems applicable to a wide array of commercial electronics and defense applications. In this work, we demonstrate the growth of crystalline SrTiO3 (STO) thin films on high-electron-mobility transistor (HEMT) heterostructures based on an emergent UWBG semiconductor ScAlN, used as the barrier layer on a GaN channel, and determine the effects of the pre-growth chemical treatments of the ScAlN surface on resultant heterostructure properties. We investigate wet chemical cleans of ScAlN with solvents, piranha solution, UV ozone and hydrofluoric acid, and a sulfuric-phosphoric acid mix prior to STO growth, and show that the commonly used piranha solution degrades the ScAlN surface, thereby reducing the crystal quality of the deposited STO layers and lowering the channel mobility. We determine that among the treatments studied, the solvent and sulfuric-phosphoric acid cleans were the least disruptive to the electrical properties of the GaN channel as evidenced from Hall effect measurements, but the sulfuric-phosphoric acid clean results in best oxide crystallinity, as determined from structural characterizations. We perform transmission electron microscopy imaging on the piranha-treated and sulfuric-phosphoric-treated samples to compare the microstructure and find that while intermixing occurs at the oxide-nitride interfaces for both samples, the interface roughness is lower and the STO grain size is larger in the sample with sulfuric-phosphoric acid treatment. This work demonstrates the first epitaxial growth of STO on an UWBG semiconductor and motivates STO/ScAlN/GaN as material platforms for high-frequency, high-power-density HEMTs. [ABSTRACT FROM AUTHOR]

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductorssilicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistoran electronic gain elementto be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistancea feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family., Author(s): Rusen Yan (corresponding author) [1]; Guru Khalsa [2]; Suresh Vishwanath [1]; Yimo Han [3]; John Wright [2]; Sergei Rouvimov [4]; D. Scott Katzer [5]; Neeraj Nepal [5]; Brian P. [...]

Tantalum nitride (γ-Ta2N) thin films were grown by radiofrequency plasma molecular beam epitaxy (MBE) on 3 in. diameter 6H- or 4H-SiC substrates. Epitaxial characteristics of these MBE grown layers were determined using high resolution x-ray diffraction (HRXRD) and transmission electron microscopy (TEM) measurements. HRXRD, TEM, and XRD reciprocal space map measurements show that γ-Ta2N on SiC grows pseudomorphically and stabilizes to a nearly pure γ-Ta2N phase. Structural properties of these layers are uniform across the 3 in. wafer diameter. Measured a and c lattice parameter values of a 43 nm thick γ-Ta2N film on 6H-SiC are 3.079 and 4.898 Å, respectively, and the film has an in-plane tensile strain of 1.03%. MBE growth of AlN/ γ-Ta2N /SiC heterostructures has also been demonstrated. Measured lattice a and c constants of AlN on γ-Ta2N /SiC are 3.120 and 4.974 Å, respectively. TEM and XRD show that SiC substrate and γ-Ta2N films have parallel epitaxial relation. [ABSTRACT FROM AUTHOR]

Epitaxial integration of perovskite oxide materials with GaN has unlocked the potential to improve functionality and performance in high-power RF and power-switching applications. In this work, we demonstrate structural and electrical properties of high dielectric constant Sr1−xCaxTiO3 epitaxial layers grown on AlGaN/GaN/4H-SiC high-electron-mobility transistor structures with compositions ranging from x = 0 to x = 0.53 and oxide film thicknesses ranging from 7 to 126 nm. We show (111) orientation in the SrCaTiO3 (SCTO) thin films using a 1 nm (100) TiO2 buffer layer grown by RF-plasma-assisted oxide molecular beam epitaxy. Current–voltage measurements show up to 5 orders of magnitude reduced leakage with SCTO films when compared to Schottky contacted samples. Capacitance–voltage measurements show minimal hysteresis, an extracted dielectric constant (κ) as high as 290, and a fixed positive interface charge density of 2.38 × 1013 cm−2 at the SCTO/AlGaN interface. The direct integration of the SCTO layer does not significantly affect the two-dimensional electron gas (2DEG) density or the channel mobility with the 2DEG density as a function of SCTO thickness having good agreement with 1D Poisson–Schrödinger simulations. RF characterization of interdigitated capacitors using the SCTO films on unintentionally doped GaN/SiC shows that the films maintain their high κ into microwave frequencies and only exhibit a slight reduction in κ with increased lateral electric fields. These results demonstrate that the integration of a high-κ oxide with GaN can potentially improve electric field management in RF high-electron-mobility transistors and increase the device breakdown voltage without significant degradation to channel transport properties. [ABSTRACT FROM AUTHOR]

This case describes a 74-year-old male who presented with rapid atrial flutter in association with large atrial lipoma along the interatrial septum. Conversion to sinus rhythm revealed the electrocardiographic criteria for advanced interatrial block. Interatrial block results from disruption of conduction through Bachmann's bundle, most commonly due to progressive atrial fibrosis. Bayés syndrome is recognized as the association of atrial arrhythmias with underlying interatrial block. This case supports the concept that localized disruption of atrial conduction via Bachmann's bundle from an atrial lipoma can produce the electrophysiologic substrate for atrial arrhythmias and the Bayés syndrome. [ABSTRACT FROM AUTHOR]