Browsing by Author "Cho, Kyeongjie"
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Item In Situ Study of E-Beam Al And Hf Metal Deposition on Native Oxide InP (100)Dong, Hong; Santosh, KC; Azcatl, Angelica; Cabrera, Wilfredo; Qin, Xiaoye; Brennan, Barry; Zhernokletov, Dmitry; Cho, Kyeongjie; Wallace, Robert M.The interfacial chemistry of thin Al (∼3 nm) and Hf (∼2 nm) metal films deposited by electron beam (e-beam) evaporation on native oxide InP (100) samples at room temperature and after annealing has been studied by in situ angle resolved X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. The In-oxides are completely scavenged forming In-In/In-(Al/Hf) bonding after Al and Hf metal deposition. The P-oxide concentration is significantly decreased, and the P-oxide chemical states have been changed to more P-rich oxides upon metal deposition. Indium diffusion through these metals before and after annealing at 250 °C has also been characterized. First principles calculation shows that In has lower surface formation energy compared with Al and Hf metals, which is consistent with the observed indium diffusion behavior.Item In Situ Study of the Role of Substrate Temperature during Atomic Layer Deposition of HfO2 on InP(2013-10-16) Dong, Hong; Santosh, KC; Qin, Xiaoye; Brennan, Barry; McDonnell, Steven; Zhernokletov, Dmitry; Hinkle, Christopher L.; Kim, Jiyoung; Cho, Kyeongjie; Wallace, Robert M.; 70133685 (Kim, J)The dependence of the "self cleaning" effect of the substrate oxides on substrate temperature during atomic layer deposition (ALD) of HfO₂ on various chemically treated and native oxide InP (100) substrates is investigated using in situ X-ray photoelectron spectroscopy. The removal of In-oxide is found to be more efficient at higher ALD temperatures. The P oxidation states on native oxide and acid etched samples are seen to change, with the total P-oxide concentration remaining constant, after 10 cycles of ALD HfO₂ at different temperatures. An (NH₄)₂ S treatment is seen to effectively remove native oxides and passivate the InP surfaces independent of substrate temperature studied (200°C, 250°C and 300°C) before and after the ALD process. Density functional theory modeling provides insight into the mechanism of the changes in the P-oxide chemical states.Item Threshold Voltage Modulation of a Graphene–ZnO Barristor Using a Polymer Doping Process(Blackwell Publishing Ltd, 2019-05-06) Kim, S. -Y; Hwang, Jeongwoon; Kim, Y. J.; Hwang, H. J.; Son, M.; Revannath, N.; Ham, M. -H; Cho, Kyeongjie; Lee, B. H.; 0000-0003-2698-7774 (Cho, K); Hwang, Jeongwoon; Cho, KyeongjieA method to modulate the threshold voltage of a graphene–ZnO barristor is investigated. Two types of polymers, polyethyleneimine (as an n-type dopant) and poly(acrylic acid) (as a p-type dopant), are used to pre-set the initial Fermi level of the graphene. The threshold voltage of the graphene barristor can be modulated between −2.0 V (n-type graphene) and 1.2 V (p-type graphene) while modulating the Fermi level of the graphene by 120 meV. This process provides a scalable and facile method to adjust the threshold voltage of graphene–semiconductor junction-based devices, which is a crucial function required to implement graphene-based electronic devices in integrated circuits. ©2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim