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Hannah Bardolaza,Jessica Afalla,Alexander De Los Reyes,Deborah Anne Lumantas,John Daniel Vasquez,Joselito Muldera,Valynn Katrine Mag-usara,Armando Somintac,Arnel Salvador,Masahiko Tani,Elmer Estacio 한국물리학회 2019 Current Applied Physics Vol.19 No.6
An externally applied magnetic field was used to induce increased photocarrier transport along the high mobility channel in GaAs/AlGaAs modulation-doped heterostructures (MDH). The terahertz (THz) emission from GaAs/ AlGaAs MDH increases with increasing magnetic field, applied parallel to the heterojunction. The THz emission enhancement factors due to the magnetic field in MDH are higher than in undoped GaAs/AlGaAs heterojunction and in bulk SI-GaAs. This demonstrates that properly utilizing the high-mobility channel for carrier transport promises to be a viable design consideration for efficient THz photoconductive antenna (PCA) devices. Moreover, it was observed that for MDH, as well as for an undoped GaAs/AlGaAs heterojunction, the enhancement for one magnetic field direction is greater than the enhancement for the opposite direction. This is in contrast to the symmetric enhancement with magnetic field direction observed in a bulk SI-GaAs. An analysis of photocarrier trajectories under an external magnetic field supports the explanation that the enhancement asymmetry with magnetic field direction in MDH is due to the cycloid motion of electrons as affected by the GaAs/AlGaAs interface.
Melvin John F. Empizo,Kohei Yamanoi,Kazuhito Fukuda,Ren Arita,Yuki Minami,Toshihiko Shimizu,Nobuhiko Sarukura,Tsuguo Fukuda,Alexandra B. Santos-Putungan,Ray M. Vargas,Arnel A. Salvador,Roland V. Sarma 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.1
Photoluminescence properties of bulk and microstructured ZnO crystals are investigated for potential scintillator applications. A bulk crystal is prepared by hydrothermal method, while hexagonal micron-sized crystals are prepared by aqueous chemical growth and carbothermal reduction methods. The bulk sample exhibits UV emission only, while the microstructured samples exhibit both UV and visible emissions. The ZnO microstructures have faster near-band edge emission lifetimes of 100 to 800 ps compared to 440 ps and 2 ns of bulk ZnO. No direct correlation between the defect-related emissions and the near-band edge emission has been observed. ZnO microstructures with fast luminescence lifetimes have promising applications as EUV lithography and XFELs scintillators.
Cafe Arven I.,De Los Reyes Alexander,Lopez Lorenzo,Husay Horace Andrew,Faustino Maria Angela,Mag-usara Valynn Katrine,Tani Masahiko,Salvador Arnel,Somintac Armando,Estacio Elmer 한국물리학회 2023 Current Applied Physics Vol.50 No.-
We demonstrate the use of the terahertz time-domain spectroscopy (THz-TDS) as a complementary tool in detecting the naturally formed oxide (NFO) layer on a copper metal surface. The THz emission from Cu-metal sheets having NFO were compared with Cu-sheets that were rapidly oxidized between temperatures ranges from 100 ◦C to 500 ◦C for 2 h. Raman spectroscopy and scanning electron microscopy were initially utilized as standard techniques for characterizing the oxide layer. However, the two performed standard techniques could not provide distinguishable results between the NFO and the thin oxide layer grown at temperatures below 200 ◦C. The THz-TDS provides clear results for non-destructive detection of the NFO on the Cu-surface. Excitation-power dependence and magnetic field dependence measurements revealed that the dominant THz emission mechanism is diffusion for CuxO formed below 300 ◦C and drift for thicker oxides grown at temperatures greater than 400 ◦C. The carrier diffusion and carrier drift mechanism are also dependent on the absorption efficiency and structural properties of the oxide layer that was formed. No THz radiation mechanism originating form nonlinear optical process was observed.