This paper describes a mechanism to explain the lattice bowing of freestanding GaN substrates grown by hydride vapor phase epitaxy on sapphire substrates. The freestanding GaN substrates typically exhibit a concave shape. It is revealed that the radius of curvature and lattice constant of the top surface are almost the same as those of the bottom surface. This is indicative of the complete relaxation of the GaN lattice, even though the freestanding GaN substrate exhibited a curvature. It is shown that dislocations are present in a plane normal to the growth direction in addition to conventionally known threading dislocations; these are referred to as in-plane dislocations. Based on these results, it is proven quantitatively that the extra-half planes related to the in-plane dislocations are primarily responsible for the phenomenon of lattice bowing.

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The interrupter technique, the simplest method for measuring airflow resistance (R int ) is particularly valuable under field conditions. We investigate whether during tidal breathing, variations in the flow at which interruption occurs contribute to variability of results. Using a portable device with mouthpiece, sets of 10 measurements of R int (R int,mo ) were made in inspiration and expiration at 0.05 l s −1 intervals from 0.1 up to 0.9 l s −1 flow in 22 normal adults, 11 children (5-9 years) and 12 COPD patients. R int was also measured via nasal-mask in normal adults (R int,na ). Intra-subject coefficient of variation was obtained at each flow and flow-dependence of R int was assessed. In normal subjects, R int -flow relationships were consistent, with a narrow range of absolute values. R int,na , but not R int,mo , rose with increasing flow, especially >0.4 l s −1 . Repeatability was poor at flows <0.3 l s −1 but improved with increasing flow and was better in inspiration than expiration. In children, repeatability was better than in adults and R int,mo was not flow dependent at 0.4 l s −1 . By contrast, in COPD patients repeatability was less good and R int,mo increased with increasing flows. R int,mo and R int,na should be measured at fixed inspiratory flows. The best signal-to-noise ratios were obtained at 0.4 l s −1 for R int in normal adults and COPD patients and at 0.3 l s −1 in children.

We investigated both the atomic arrangements in the core structure of threading dislocations (TDs) and their behaviors in unintentionally doped c-plane-GaN layers grown by metalorganic vapor phase epitaxy and hydride vapor phase epitaxy using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The extra image contrast near the core was attributed to an extra displacement in a-type TDs in addition to the core structures revealed in previous reports; we used the notation “with displacement” to describe the new core structure. We found that TDs incline towards both the m- and a-directions from the c-direction. The transition of a-type TDs from the conventional core structure to the structure with displacement was deduced from its relationship to the TD inclination. We also found similarities between a-type screw dislocations and a-type TDs with displacement in the atomic-scale HAADF-STEM images. We concluded that a-type TDs could incline towards the a-direction via a-type screw dislocations, and that these inclined a-type TDs are observed as the core structure with displacement.