Browsing by Author "Carlson, Eric"

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    Connection between Carbon Incorporation and Growth Rate for GaN Epitaxial Layers Prepared by OMVPE
    Ciarkowski, Timothy; Allen, Noah P.; Carlson, Eric; McCarthy, Robert; Youtsey, Chris; Wang, Jingshan; Fay, Patrick; Xie, Jinqiao; Guido, Louis J. (MDPI, 2019-08-01)
    Carbon, a compensator in GaN, is an inherent part of the organometallic vapor phase epitaxy (OMVPE) environment due to the use of organometallic sources. In this study, the impact of growth conditions are explored on the incorporation of carbon in GaN prepared via OMVPE on pseudo-bulk GaN wafers (in several cases, identical growths were performed on GaN-on-Al2O3 templates for comparison purposes). Growth conditions with different growth efficiencies but identical ammonia molar flows, when normalized for growth rate, resulted in identical carbon incorporation. It is concluded that only trimethylgallium which contributes to growth of the GaN layer contributes to carbon incorporation. Carbon incorporation was found to decrease proportionally with increasing ammonia molar flow, when normalized for growth rate. Ammonia molar flow divided by growth rate is proposed as a reactor independent predictor of carbon incorporation as opposed to the often-reported input V/III ratio. A low carbon concentration of 7.3 × 1014 atoms/cm3 (prepared at a growth rate of 0.57 µm/h) was obtained by optimizing growth conditions for GaN grown on pseudo-bulk GaN substrates.
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    Electrical characterization of RuOx/n-GaN Schottky diodes formed by oxidizing ruthenium thin-films in normal laboratory air
    Allen, Noah P.; Ciarkowski, Timothy; Carlson, Eric; Chakraborty, Amrita; Guido, Louis J. (2020-01)
    Schottky diodes were formed by oxidizing Ru thin films deposited on n-type GaN at 400, 500, and 600 degrees C in normal laboratory air, and their electrical behavior was compared to that of a Ru/n-GaN reference device. The GaN epitaxial layers were grown via metalorganic chemical vapor deposition. The ruthenium films were deposited by electron beam evaporation. The Schottky barriers were characterized via current vs voltage (IV) and deep-level transient spectroscopy (DLTS) measurements between 70 and 400 K. The temperature dependent forward bias IV characteristics were fit, and the extracted temperature dependence of the effective barrier height for each device was shown to be caused by inhomogeneity at the metal/semiconductor interface. It was found that barrier inhomogeneity could be well described by a modified log-normal distribution. In reverse bias, it was shown that the low-energy tail of the barrier distribution is an important factor in determining leakage current. Favorable results occur for diodes oxidized at 400 and 500 degrees C, but raising the oxidation temperature to 600 degrees C results in a drastic increase in leakage current. DLTS measurements reveal one electron trap at E-C - 0.57 eV in each of the samples. It was found that the concentration of this 0.57 eV trap increases substantially at 600 degrees C and that trap-assisted tunneling likely contributes an additional pathway for reverse leakage current. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).