Using in‐house synthesized poly(dodecamethylene terephthalate) (P12T) as a model, periodic extinction‐banded spherulites melt‐crystallized at high Tcs (100–115 °C) are expounded in terms of growth mechanism. The extinction‐banded spherulites wildly differing from the usual blue/orange double ring‐banded spherulites are composed of all flat‐on discrete single‐crystalline lamellae packed like roof shingles (or fish scales) along the circularly curved bands and the lamellae in the extinction bands are flat with a lozenge shape with no continuous twisting at all. For P12T films of more than 10 µm crystallized at Tc = 105–115 °C, no periodic bands were seen, and all spherulites were ringless, where periodic growth precipitation of crystals to extinction does not occur until impingement. Extinction bands in the P12T spherulites with the inter‐ring spacing steadily decrease with decreasing film thickness, because for thinner films (submicrons to 2 µm), draining or depletion of available molten species takes place more frequently, leading to bands of smaller inter‐ring spacing. The petal‐like extinction bands are discussed and analyzed in detail using 3D AFM imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 601–611

GaN n+–p junction diodes were fabricated by implanting Si atoms into p-GaN. It was shown that we could use these diodes as GaN-based planar photodetectors. It was found that the dark current density of the diodes was around 1.5 μA/cm2 and 50 nA/cm2 at reverse biases of 3 and 1 V, respectively. Spectra response measurements revealed a cutoff wavelength at around 365 nm and a peak responsivity of 0.33 mA/W at 365 nm for the GaN planar n+–p photodetectors. It was also found that the visible rejection ratio was around 260. Furthermore, temporal response measurements revealed that the fall times of these GaN planar n+–p photodetectors were found to be shorter than 0.4 μs.

Polarized optical, atomic force, and scanning electron microscopy images showing the correlations of three-dimensional crystal arrangements with optical properties exhibited by poly(dodecamethylene terephthalate).

Articles you may be interested inEffects of annealing temperature on the characteristics of Ga-doped ZnO film metal-semiconductor-metal ultraviolet photodetectors J. Appl. Phys. 113, 084501 (2013); 10.1063/1.4791760 Performance improvement of GaN-based ultraviolet metal-semiconductor-metal photodetectors using chlorination surface treatment J. Vac. Sci. Technol. B 30, 031211 (2012); 10.1116/1.4711215Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors Very low dark current metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN epitaxial layers Gallium nitride ͑GaN͒ ultraviolet metal-semiconductor-metal photodetectors ͑PDs͒ grown on Si substrates were demonstrated. The dark current of PDs fabricated on Si substrates was substantially smaller in magnitude compared to identical devices prepared on sapphire substrates. With an incident wavelength of 359 nm, the maximum responsivities of the n − -GaN MSM photodetectors with TiW and Ni/ Au contact electrodes were 0.187 and 0.0792 A / W, corresponding to quantum efficiencies of 64.7% and 27.4%, respectively. For a given bandwidth of 1 kHz and a given bias of 5 V, the corresponding noise equivalent powers of our n − -GaN MSM photodetectors with TiW and Ni/ Au electrodes were 1.525ϫ 10 −12 and 5.119ϫ 10 −12 W, respectively. Consequently, the values of detectivity ͑D * ͒ determined for devices with TiW and Ni/ Au electrodes were then calculated to be 1.313ϫ 10 12 and 3.914ϫ 10 11 cm Hz 0.5 W −1 , respectively.