The Oxford-Diamond In Situ Cell for studying chemical reactions using time-resolved X-ray diffraction Rev. Sci. Instrum. 83, 084101 (2012) Synchrotron-based ultrafast x-ray diffraction at high repetition rates Rev. Sci. Instrum. 83, 063303 (2012) Shortening x-ray pulses for pump-probe experiments at synchrotrons J. Appl. Phys. 109, 126104 (2011) High-pressure and high-temperature x-ray diffraction cell for combined pressure, composition, and temperature measurements of hydrides Rev. Sci. Instrum. 82, 065108 (2011) High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy Rev. Sci. Instrum. 82, 063106 (2011) Additional information on Appl. Phys. Lett.

Defect structures were investigated by transmission electron microscopy for GaN/Al2O3 (0001) epilayers grown by metal-organic chemical vapor deposition using a two-step process. The defect structures, including threading dislocations, partial dislocation bounding stacking faults, and inversion domains, were analyzed by diffraction contrast, high-resolution imaging, and convergent beam diffraction. GaN film growth was initiated at 600 °C with a nominal 20 nm nucleation layer. This was followed by high-temperature growth at 1080 °C. The near-interfacial region of the films consists of a mixture of cubic and hexagonal GaN, which is characterized by a high density of stacking faults bounded by Shockley and Frank partial dislocations. The near-interfacial region shows a high density of inversion domains. Above ∼0.5 μm thickness, the film consists of isolated threading dislocations of either pure edge, mixed, or pure screw character with a total density of ∼7×108 cm−2. The threading dislocation reduction in these films is associated with cubic to hexagonal transformation of the nucleation layer region during high temperature growth.

Epitaxial lateral mask overgrowth which occurs during GaN selective epitaxy has been studied using linear mask features. The lateral growth varies between its maximum and minimum over a 30° angular span and exhibits hexagonal symmetry. Vertical growth follows an opposite trend, with lateral growth maxima, and vertical growth minima occurring for lines parallel to the GaN 〈10•0〉. Large variations in the lateral growth are also obtained through variations in the growth temperature and NH3 flow. Under proper growth conditions, lateral to vertical growth rate ratios of up to 4.1 can be achieved, resulting in significant lateral mask overgrowth and coalescence of features without excessive growth times.

On the determination of the glass forming ability of AlxZr1−x alloys using molecular dynamics, Monte Carlo simulations, and classical thermodynamics J. Appl. Phys. 112, 073508 (2012) Enhanced photoanode properties of epitaxial Ti doped α-Fe2O3 (0001) thin films Appl. Phys. Lett. 101, 133908 (2012) Structure and optical band gap of ZnO1−xSx thin films synthesized by chemical spray pyrolysis for application in solar cells J. Appl. Phys. 112, 063708 (2012) Roto-flexoelectric coupling impact on the phase diagrams and pyroelectricity of thin SrTiO3 films J. Appl. Phys. 112, 064111 (2012) Plasmonic effects of ultra-thin Mo films on hydrogenated amorphous Si photovoltaic cells

We report record high breakdown voltages up to 340 and 230 V realized on unintentionally doped (1.5 μm gate length) and Si doped (1 μm gate length) AlGaN/GaN modulation doped field effect transistors (MODFETs), respectively. The devices also have large transconductances up to 140 mS/mm and a full channel current of 150–400 mA/mm. The Si doped MODFET sample demonstrated a very high room temperature mobility of 1500 cm2/Vs. With these specifications, GaN field effect transistors as microwave power devices are practical.