Atom probe tomography was used to characterize AlN interlayers in AlGaN/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy (PAMBE), NH3-based molecular beam epitaxy (NH3-MBE), and metal-organic chemical vapor deposition (MOCVD). The PAMBE-grown AlN interlayer had the highest purity, with nearly 100% of group-III sites occupied by Al. The group-III site concentrations of Al for interlayers grown by NH3-MBE and MOCVD were ∼85% and ∼47%, respectively. Hall measurements were performed to determine the two-dimensional electron gas mobility and sheet concentration. Sheet concentrations were ∼25%–45% higher with molecular beam epitaxy than with MOCVD, and these results matched well with atom probe data.

In Bangladesh, use of beauty cream is very much popular and a common daily task for the people. The current study is focusing on the assessment of some toxic heavy metals such as lead, cadmium, chromium, and mercury contamination in some beauty creams commonly used by Bangladeshi people. The results indicate that the concentrations of lead, cadmium, and chromium exceed the maximum allowable concentrations, whereas mercury is found below the acceptable limit set by WHO/EU. However, according to Health Canada, the concentrations of cadmium and chromium for all the selected samples (except cadmium in sample coded A) was within the permissible limit. Health risks associated with these metal intakes via dermal exposure route are evaluated in terms of chronic daily intake (CDI) and hazard quotient (HQ). The carcinogenic risk (CR) estimated for chromium indicates that it is within the acceptable range. The cancer and non-cancer risk results indicate that although the chances of cancer risk and non-cancer risk resulting from the use of these cosmetic products were unlikely, buildup of these toxic heavy metals overtime on continuous usage could be detrimental for Bangladeshi people.

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Metal-polar In 0.17 Al 0.83 N barriers, lattice-matched to GaN, were grown under N-rich conditions by plasma-assisted molecular beam epitaxy. The compositional homogeneity of these barriers was confirmed by plan-view high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Metal-polar In 0.17 Al 0.83 N/(GaN)/(AlN)/GaN structures were grown with a range of AlN and GaN interlayer (IL) thicknesses to determine the optimal structure for achieving a low two-dimensional electron gas (2DEG) sheet resistance. It was determined that the presence of a GaN IL was necessary to yield a 2DEG sheet density above 2 × 10 13 cm −2 . By including AlN and GaN ILs with thicknesses of 3 nm and 2 nm, respectively, a metal-polar In 0.17 Al 0.83 N/GaN/AlN/GaN structure regrown on a GaN-on-sapphire template yielded a room temperature (RT) 2DEG sheet resistance of 163 / . This structure had a threading dislocation density (TDD) of ∼5 × 10 8 cm −2 . Through regrowth on a free-standing GaN template with low TDD (∼5 × 10 7 cm −2 ), an optimized metal-polar In 0.17 Al 0.83 N/GaN/AlN/GaN structure achieved a RT 2DEG sheet resistance of 145 / and mobility of 1822 cm 2 V −1 s −1 . High-electron-mobility transistors with output current densities above 1 A mm −1 were also demonstrated on the low-TDD structure.