Intersubband Transitions in Nonpolar GaN-based Resonant Phonon Depopulation Multiple-Quantum Wells for Terahertz Emissions
Ya-Feng Song1, Xiong-Xiong Kong1, Wei-Bin Tang1, Zhong-Qiang Suo1, Huan Zhang1, Chen-Yang Li1, Qian Jia1, Cai-Xia Xue1, Yan-Wu Lu2, Chao-Pu Yang3
1Department of Physics, College of Electronic Information and Electrical Engineering, Shangluo University, Shangzhou 726000, China
2Department of Physics, Beijing Jiaotong University, Beijing 100044, China
3College of Chemical Engineering and Modern Materials, Shangluo University, Shangzhou 726000, China
We investigate the polarization effect in intersubband transitions in polar and nonpolar GaN-based multiple-quantum well (MQW) quantum cascade (QC) structures for terahertz (THz) emissions by comparisons, and design a nonpolar GaN/Al$_{0.2}$Ga$_{0.8}$N QC structure of 7.27 THz emissions which matches the resonant phonon depopulation condition (92.7 meV) for better population inversion. It shows a lower threshold current density Jth and a higher output power at all temperatures. We also find that the Jth of the nonpolar GaN MQW QC structures increases more slowly than that of the polar ones of the same structrure as temperature increases.
J. Korean Phys. Soc. 2019; 74: 1039-1045
Influence of Bi Excess on the Structural and Morphological Properties of Bi$_{0.5}$K$_{0.5}$TiO$_3$ Synthesized by Using the Hydrothermal Method and Its Nanogenerator Properties
Seon Yong Kim1, Eun Young Kim1, Sang Don Bu1, Jin Kyu Han2, Da Som Song2, Jongsun Lim2, Ki-Seok An2
1Department of Physics and Research Institute of Physics and Chemistry, Chonbuk National University, Jeonju 54896, Korea
2Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Korea
We investigated the effects of an excess of bismuth in Bi$_{0.5}$K$_{0.5}$TiO$_3$ (BKT) on its structural and morphological properties. Two types of BKT samples were prepared using bismuth stoichiometry, where one with a Bi:K molar ratio of 1:1 (S-BKT) and the other with a ratio of 1.1:1 with 10 mol% excess of Bi (10% BKT). These samples were prepared using the hydrothermal synthesis method. When the X-ray diffraction (XRD) data for the two samples were compared, the 10% BKT shows a 1.3 times larger than that for the S-BKT sample in the ratio of the secondary phase peak to the BKT (101) peak at approximately 29.3$^\circ$. Morphology analysis showed that both samples had agglomerations with diameters of approximately 200 nm and nanowires with lengths of 1–2 $\mu$m and diameters of 8 nm. The fractions of the total area occupied by agglomerations in the two samples were estimated at approximately 95% for 10% BKT and approximately 45% for S-BKT. These results indicate that an excess of bismuth affects the secondary phase and agglomeration formation. Nanogenerators were prepared by mixing S-BKT, and their output voltages were 1.8 V and their outputs currents were 4 nA.
J. Korean Phys. Soc. 2019; 74: 1027-1031
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