We report on the structure study of MgxZn1−xO films and, in particular, we will focus on MgxZn1−xO layers with x=0.28 and 0.41 MgxZn1−xO layers with different crystal structures of cubic and wurtzite that have been grown by plasma-assisted molecular-beam epitaxy on MgO∕c-sapphire with Mg∕Zn flux ratio control. The MgxZn1−xO films have been characterized by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction. The dependence of the cation-anion bond length to Mg content has been studied. A virtual crystal model of MgZnO has been applied to interpret the bond-length variation. HRTEM results indicate that the initial stage of the MgZnO growth on a MgO buffer layer starts with a cubic structure even in the case of a wurtzite structure at the end of growth.

AlGaN/GaN resonant tunneling diodes (RTDs), consisting of 20% (10%) aluminum-content in double-barrier (DB) active layer, were grown by metal-organic chemical vapor deposition on freestanding polar (c-plane) and nonpolar (m-plane) GaN substrates. RTDs were fabricated into 35-μm-diameter devices for electrical characterization. Lower aluminum content in the DB active layer and minimization of dislocations and polarization fields increased the reliability and reproducibility of room-temperature negative differential resistance (NDR). Polar RTDs showed decaying NDR behavior, whereas nonpolar ones did not significantly. Averaging over 50 measurements, nonpolar RTDs demonstrated a NDR of 67 Ω, a current-peak-to-valley ratio of 1.08, and an average oscillator output power of 0.52 mW.

We report on the growth, fabrication, and device characterization of AlGaN-based thin-film ultraviolet (UV) (k $ 359 nm) light emitting diodes (LEDs). First, AlN/Si(111) template is patterned. Then, a fully coalesced 7-lm-thick lateral epitaxial overgrowth (LEO) of AlN layer is realized on patterned AlN/Si(111) template followed by UV LED epi-regrowth. Metalorganic chemical vapor deposition is employed to optimize LEO AlN and UV LED epitaxy. Back-emission UV LEDs are fabricated and flip-chip bonded to AlN heat sinks followed by Si(111) substrate removal. A peak pulsed power and slope efficiency of $0.6 mW and $1.3 lW/mA are demonstrated from these thin-film UV LEDs, respectively. For comparison, top-emission UV LEDs are fabricated and back-emission LEDs are shown to extract 50% more light than top-emission ones. V

Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa24-26) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa6-Fa10) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa28-Fa38) belt. The wadsleyite-ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition (Fa24-26), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition (Fa24-26). Our findings could erase the possibility of the resulting unrealistic time scales of the highpressure regime reported recently from other shocked L-6 chondrites.focused ion beam ͉ transmission electron microscopy ͉ shocked chondrite ͉ high-pressure mineral M any highly equilibrated L-and H-chondritic meteorites display intense deformation of their mineral constituents, olivine, orthopyroxene, and plagioclase feldspars, inferred to have been produced by hypervelocity collisions of their parental asteroids with other interplanetary objects. They also contain millimeter-sized shock-melt veins interpreted to have resulted from friction along cracks or concentration of shear in glide bands as a result of the deviatoric component rather than from pressure heterogeneities during the dynamic events. The melt veins contain an inventory of high-pressure polymorphs of the major chondritic minerals olivine, orthopyroxene, and plagioclase feldspars like ringwoodite, less abundant wadsleyite, majorite, akimotoite, lingunite, and jadeite plus SiO 2 glass. In many chondrites, the matrices of these veins show the liquidus pair majorite-pyrope ss plus magnesiowüstite and FeNi metal blebs with eutectic-like intergrowth with FeS indicating crystallization from a melt of bulk chondritic composition at high pressures (Ϸ20-23 GPa) and temperatures (2,000-2,300°C) (1). The olivine-ringwoodite and olivine-wadsleyite inversions in these veins were extensively investigated due to their relevance to mechanisms in Earth's transition zone and the low...