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Strain engineering for gallium nitride has been studied by many researchers to improve the performance of various devices (i.e., light-emitting diodes, laser diodes, power devices, high electron mobility transistors, and so on). Further miniaturization of gallium nitride devices will clearly continue in the future, and therefore an accurate understanding of the strain state in the devices is essential. However, a measurement technique for axially resolved evaluation of the strain in microareas has not yet been established. In this study, we revealed that the anisotropic strain state induced in c-plane growth gallium nitride is linked to the split state of Raman peaks, which were measured with z (x x) z ¯ and z (y x) z ¯ polarized configurations. The anisotropic strain state in c-plane gallium nitride was induced in the 3D-structure by epitaxial lateral overgrowth, which enabled successful performance of our work. This result allowed us to axially decompose the strain in c-plane gallium nitride through Raman spectroscopy and establish a measurement technique for axially resolving the strain. This measurement technique is feasible using a conventional Raman spectrometer. Furthermore, the method was indicated to be applicable to all wurtzite-type crystals, including gallium nitride, silicon carbide, and aluminum nitride. Our work provides a new perspective for understanding the complex strain state in microareas for wurtzite materials. Comprehending the strain state, which strongly affects device performance, will help promote the research and development of III-V semiconductor devices. [ABSTRACT FROM AUTHOR]

A light-weight Wolter type-I telescope for future space X-ray observations is prototyped by using micromachining technologies. Curvilinear micro pores with a width of 20 $$\upmu$$ m are fabricated with deep reactive ion etching. Sidewalls of the pores are smoothed with high temperature annealing. Then, two wafers are deformed to different curvature radii, 1000 and 333 mm. The two wafers are aligned using parallel X-ray beams which are dominated by Al-K $$_{\alpha }$$ line at 1.49 keV. High angular and positional accuracies of the order of arcsec and $$\upmu$$ m are achieved using movable stages. The first clear X-ray focusing is confirmed. Its angular resolution is 4.1 arcmin in full width half maximum while it is at least 92 arcmin in half power width. The effective area is 19.0 mm $$^2$$ which is $$\sim$$ 5 times smaller than a model calculation. We discuss causes of the degraded angular resolution and effective area and also future improvements. [ABSTRACT FROM AUTHOR]