Intersubband Transitions in Nonpolar GaN-based Resonant Phonon Depopulation Multiple-Quantum Wells for Terahertz Emissions
We investigate the polarization effect in intersubband transitions in polar and nonpolar GaN-based multiple-quantum well (MQW) structures for terahertz (THz) emissions by using systematic comparisons and design a nonpolar GaN/Al0.2Ga0.8N two-well-based MQW structure with an emitting photon of 7.27 THz (30.07 meV). Its lower energy separation (92.7 meV) matches the resonant phonon depopulation condition for better population inversion. It shows a lower threshold current density Jth at all temperatures (1.548 kA/cm2 at 90 K) and a higher output power of up to 86.1 mW at 5.8 K and 33.6 mW at 100 K. Our results for the polar GaN MQW are very close to the experimental data in the literature. We find that the Jth of the nonpolar GaN MQW increases more slowly than that of the polar GaN MQW as temperature increases, indicating the nonpolar GaN MQW may be a worth-trying direction for improving the operation temperature. These results can provide meaningful references for the design and fabrication of nonpolar GaN-based THz MQW or quantum cascade structures.
KeywordsNonpolar GaN multiple-quantum well Resonant phonon depopulation Terahertz intersubband transitions Quantum cascade structures
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The authors would like to thank Prof. Hongming Zhang, Lai Wang and Zhibiao Hao greatly for helpful discussions; Kamran Rajabi, Jiadong Yu, Xun Wang, Lei Wang et al. in Tsinghua National Laboratory on Information Science and Technology and Department of Electronic Engineering for great help in this work; the National Natural Science Foundation of China (No. 61864 008), Natural Science Basic Research Plan in Shaanxi Province of China (No. 2017JQ6011), Shanghai Young College Teachers Training Scheme (No. ZZSDJ13004), and Shangluo University Science and Technology Research Fund Project (No. 15SKY025) for financial support.
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