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주범수,한문섭,장영준,Jong Hoon Shin,Seung Yup Jang,Taehoon Jang 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.12
For GaN/AlGaN/GaN heterostuructures grown on Si substrates, we investigated the changesin the chemical compositions during photochemical oxidation. We utilized synchtrotron-basedhigh-resolution X-ray photoemission spectroscopy to precisely analyze the stoichiometry change. Epitaxially-grown GaN/AlGaN/GaN multilayer films showed a single-crystalline structure and thedominant bonding character of Ga-N near the surface. After photoelectrochemical oxidation withdeionized water, the Ga-N bonding transformed into the Ga-O bonding, in which the stoichiometrywas confirmed to be Ga2O3. Thus, photoelectrochemical oxidation with water may be a goodcandidate for fabricating the gate dielectric layer, Ga2O3, for GaN-based power transistors.
Evidence for indirect band gap in BaSnO3 using angle-resolved photoemission spectroscopy
주범수,장영준,Luca Moreschini,Aaron Bostwick,Eli Rotenberg,한문섭 한국물리학회 2017 Current Applied Physics Vol.17 No.5
Transparent BaSnO3 thin films have been proposed as an alternative transparent conducting oxide (TCO). Although bulk synthesis and high-quality fabrication of epitaxial films are well established, there are still unsolved aspects about their electronic structure, such as the direct or indirect nature and the size of the band gap. We investigated the electronic structure of epitaxial BaSnO3 thin films using in situ angleresolved photoemission spectroscopy. We directly measured an indirect band gap of 3.7 eV, a value compatible with those of previous reports, but we also identified additional in-gap states at 1.6 eV below the conduction band minimum that we attribute to intrinsic defects, mainly oxygen vacancies.
Excimer laser annealing effects on AlGaN/GaN heterostructures
이인학,주범수,김혁진,윤예슬,장선엽,강민규,강종윤,박병규,한문섭,장영준 한국물리학회 2016 Current Applied Physics Vol.16 No.6
We investigated impact of excimer laser annealing on the AlGaN/GaN heterojunction structures, where the 2-dimensional electron gas (2DEG) is formed. When applying homogeneous laser pulses at various laser densities, the electrical resistance of the 2DEG shows sudden increase along with sharp decrease of the carrier mobility and slight decrease of the carrier density. Especially, when applying laser density of 300 mJ/cm2, we could obtain such jump of electrical resistance even after 2 min, i.e. 2400 pulses at 20 Hz. Low temperature photoluminescence and x-ray photoemission spectroscopy measurements show that the excimer laser annealing suppresses the coherent charge carriers and oxides the sample surface to form Ga2O.We estimate the activation energy of suppressing 2DEG to be 0.89 eV for the ELA process. We suggest that the excimer laser annealing has potential for gate oxide fabrication, surface passivation, and lateral pattering of 2DEG structures.