The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-inch diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4-and 6-inch, c-axis single-crystal sapphires from full-diameter seeds.

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We performed the time-domain measurement of lasing spectrum in a GaInAsP photonic crystal nanolaser. We observed a very wide wavelength chirping up to 10 nm, which can be explained by a strong TO effect. IntroductionPhotonic crystal (PC) nanolasers are extensively studied because of their ultralow threshold, spontaneous emission control, etc. For these lasers, we often observe a very wide spectrum even above threshold under pulsed pumping condition. Regarding on such a spectrum, Yoshie et al. has discussed the possibility of 100 GHz class very fast relaxation oscillation in a nanolaser due to Purcell effect [1]. In this study, we investigated the spectral characteristics of the GaInAsP quantum well PC H0 nanolaser [2] by using time domain measurement, and concluded that the strong thermal chirping occurs due to a large thermal resistance of 1 K/ W order in this device. We confirmed the consistency of results by measuring the temperature characteristics of this nanolaser.