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Guan-Bo Lin,Xiaoguang Zhang,이수민,George Papasouliotis,김종규,E. Fred Schubert,조제희 한국물리학회 2015 Current Applied Physics Vol.15 No.10
Light-emitting diodes (LEDs) with a Mg-doped p-type Ga1-xInxN (0 ≤ x ≤ 0.07) spacer layer located between an undoped GaN spacer layer and the electron blocking layer are investigated. The LEDs are found to have comparable peak efficiency but less efficiency droop when the crystal quality of the p-type Ga1-xInxN spacer layer is well-controlled by lowering the growth temperature and by using a suitable In composition and Mg doping concentration. All LED samples with the p-type spacer layer show a smaller efficiency droop compared to a reference LED having an undoped GaN spacer. Among the sample sets investigated, an optical power enhancement of 12% at 111 A/cm2 is obtained when inserting a 5 nm-thick p-type Ga0.97In0.03N spacer layer. The results support that carrier transport is the key factor in the efficiency droop observed in GaN-based LEDs.
Guan-Bo Lin,Dong-Yeong Kim,Qifeng Shan,Jaehee Cho,Schubert, E. Fred,Hyunwook Shim,Cheolsoo Sone,Jong Kyu Kim IEEE 2013 IEEE photonics journal Vol.5 No.4
<P>The dependence of the polarization-induced electric field in GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) on the GaN quantum barrier (QB) thickness is investigated. Electrostatic arguments and simulations predict that a thin QB thickness reduces the electric field in the quantum wells (QWs) and also improves the LED efficiency. We experimentally demonstrate that the QW electric field decreases with decreasing QB thickness. The lower electric field results in a better overlap of electron and hole wave functions and better carrier confinement in the QWs. A reduced efficiency droop and enhanced internal quantum efficiency is demonstrated for GaInN/GaN LEDs when the QB thickness is reduced from 24.5 to 9.1 nm.</P>
Park, Jun Hyuk,Lin, Guan-Bo,Kim, Dong Yeong,Lee, Jong Won,Cho, Jaehee,Kim, Jungsub,Lee, Jinsub,Kim, Yong-Il,Park, Youngsoo,Schubert, E Fred,Kim, Jong Kyu Optical Society of America 2015 Optics express Vol.23 No.12
<P>The efficiency of an AlGaN deep-ultraviolet light-emitting diode with peak emission wavelength of 285 nm is investigated as a function of current over a wide range of temperatures (110 K to 300 K). We find that the efficiency-versus-current curve exhibits unique and distinct features over the entire temperature range including three points of inflection. At low temperatures, the change in slope in the efficiency-versus-current curve is particularly pronounced producing a minimum in the efficiency after which the efficiency rises again. Furthermore, at high current density, the low-temperature efficiency exceeds the room-temperature efficiency. The feature-rich efficiency-versus-current curve is consistent with an enhancement in p-type conductivity by field-ionization of acceptors that occurs in the high-injection regime and is particularly pronounced at low temperatures. Differential conductivity measurements show a marked rise in the high-injection regime that is well correlated to the minimum point in the efficiency-versus-current curve.</P>
Wen-Xiao Tian,Shi Yu,Muhammad Ibrahim,Abdul Wareth Almonaofy,Liu He,Qiu Hui,Zhu Bo,Bin Li,Guan-lin Xie 한국미생물학회 2012 The journal of microbiology Vol.50 No.4
Infections by Enterobacter species are common and are multidrug resistant. The use of bactericidal surface materials such as copper has lately gained attention as an effective antimicrobial agent due to its deadly effects on bacteria,yeast, and viruses. The aim of the current study was to assess the antibacterial activity of copper surfaces against Enterobacter species. The antibacterial activity of copper surfaces was tested by overlying 5×106 CFU/ml suspensions of representative Enterobacter strains and comparing bacterial survival counts on copper surfaces at room temperature. Iron, stainless steel, and polyvinylchloride (PVC) were used as controls. The mechanisms responsible for bacterial killing on copper surfaces were investigated by a mutagenicity assay of the D-cycloserin (cyclA gene), single cell gel electrophoresis,a staining technique, and inductively coupled plasma mass spectroscopy. Copper yielded a significant decrease in the viable bacterial counts at 2 h exposure and a highly significant decrease at 4 h. Loss of cell integrity and a significantly higher influx of copper into bacterial cells exposed to copper surfaces, as compared to those exposed to the controls,were documented. There was no increase in mutation rate and DNA damage indicating that copper contributes to bacterial killing by adversely affecting cellular structure without directly targeting the genomic DNA. These findings suggest that copper’s antibacterial activity against Enterobacter species could be utilized in health care facilities and in food processing plants to reduce the bioburden, which would increase protection for susceptible members of the community.