Browsing by Author "Zhang, Dainan"
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Item Effect of Al2O3 Buffer Layers on the Properties of Sputtered VO2 Thin Films(Springer Berlin Heidelberg, 2017-02-14) Zhang, Dainan; Wen, Tianlong; Xiong, Ying; Qiu, Donghong; Wen, Qiye; Dainan Zhang, Tianlong Wen, Ying Xiong, Donghong Qiu, Qiye Wen; Zhang, DainanVO2 thin films were grown on silicon substrates using Al2O3 thin films as the buffer layers. Compared with direct deposition on silicon, VO2 thin films deposited on Al2O3 buffer layers experience a significant improvement in their microstructures and physical properties. By optimizing the growth conditions, the resistance of VO2 thin films can change by four orders of magnitude with a reduced thermal hysteresis of 4 C at the phase transition temperature. The electrically driven phase transformation was measured in Pt/Si/Al2O3/VO2/Au heterostructures. The introduction of a buffer layer reduces the leakage current and Joule heating during electrically driven phase transitions. The C–V measurement result indicates that the phase transformation of VO2 thin films can be induced by an electrical field.Item Infrared and terahertz dual band semiconductor development and spin orbitronics based on semiconductors and insulators(University of Delaware, 2018) Zhang, DainanThe rapid development of photoelectric detection technology calls for a new generation of semiconductor films working in both infrared and terahertz bands. We explored Ge1-xRx (R=Bi, Sn) dual band photoelectric devices. Through the doping of high Sn content, induced direct bandgap appears and the infrared light responsivity of the sample reaches to 0.60A/W at 2.2μm wavelength, and transmission in terahertz can be modulated. We have also successfully grown n-type GeBi semiconductor alloy thin films for the first time. The optimum Bi doping amount is between 2%-18%. Direct bandgap has also been induced with Bi doping that broaden the operation frequency at infrared. The GeBi films show a large light responsivity and the Bi-dopant dependent transmission at 0.3-0.8 THz terahertz. We have also fabricated Ge1-xSnx PIN and Ge1-yBiy PN devices working in both infrared and terahertz with relatively low dark current density, large modulation depth and fast modulation rate in terahertz from 0.1 to 1.0 THz. ☐ Bi dopants in semiconductors and insulators are known to introduce large spin orbit coupling, which has recently been applied in spin electronics, known as spintronics to produce pure spin currents to switch the magnetization in a magnetic layer. This has become an enabling technique to develop next generation non-volatile magnetic random-access memory (MRAM) or logic devices. The spin-orbit coupling in GeBi films was investigated by inject spin current via precessing the magnetization of a neighboring NiFe or Yttrium Iron Garnet (YIG) layer using ferromagnetic resonance. Large inverse spin Hall voltage has been observed due to the large SOC in GeBi layer. We further investigate the Bi doped magnetic insulator Thulium Iron Garnet (Bi:TmIG) to promote the out-of-plane magnetizations which is commonly used in spintronic applications. We have successfully grown single crystal and textured Bi:TmIG using liquid epitaxy and magnetron sputtering techniques. The current-induced spin orbital torques has been studied via the first- and second-order harmonic Hall voltage measurements in Bi:TmIG/Pt. The spin torque efficiency is much larger compared with metallic ferromagnet/Pt bilayer systems.