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Da-Ren Hang,M. Heuken,M.C. Chou,M.H. Hsieh 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
We study the influence of a buffer layer on the optical properties of InGaN/GaN multiple quantum wells (MQWs) grown on silicon substrates by using metalorganic vapor phase epitaxy. To overcome the large lattice mismatch and the difference in the thermal expansion coefficients by which a high dislocation density occurs, we grow the MQWs on an advanced buffer structure consisting of low-temperature (LT) AlN and a high-temperature (HT) AlN/AlGaN/GaN stack. The Raman spectra confirm that the biaxial tensile strain is reduced by the insertion of the alternating LT and HT buffer layers. Moreover, we find the room-temperature internal quantum efficiency can be improved. Our results suggest that the enhanced optical performance comes from the reduced number of nonradiative recombination centers brought about by the LT and HT composite buffer layers.
Controlling Band Gap and Refractive Index in Dopant-Free α-Fe2O3 Films
Pawan Kumar,Nitin Rawat,Da-Ren Hang,이흥노,Rajesh Kumar 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.1
Dopant-free hematite (α-Fe2O3) films are formed at a liquid-vaporinterface by means of an easy method in order to control the bandgap and refractive index of the films. The α-Fe2O3 films after beingtransferred to a glass substrate are studied for their structural andoptical properties. Control over the thickness of the films in therange from 75 to 400 nm and the constituent nanocrystallite sizefrom 3 to 46 nm is achieved by controlling the synthesisparameters. By controlling the film thickness, crystallite size, andcrystallinity of dopant-free α-Fe2O3 films, the optical band gap isincreased significantly (by ≈ 0.64 eV) from 2.30 to 2.94 eV, alongwith increase in the refractive index from 1.35 to 2.8. Theobserved increase in the optical band gap is explained on thebasis of change in lattice symmetry (via change in the c/a ratio) ofα-Fe2O3 crystallites.
Jing-Han Chen,Chi-Te Liang,Chun-Feng Huang,Da-Ren Hang,David A. Ritchie,J. C. Hsiao,Jyun-Ying Lin,Michelle Y. Simmons,Ming-Gu Lin,S. H. Lo,Tsai-Yu Huang 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems (2DESs), we study the low-field Landau quantization when the thermal damping is reduced with decreasing temperature. Magneto-oscillations following the Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results show the importance of the positive magneto-resistance to the extension of the SdH formula under the damping induced by the disorder.