A sensitivity analysis on the electron transport within zinc oxide and its device implications
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A sensitivity analysis on the electron transport within zinc oxide and its device implications Poppy Siddiqua1, Michael S. Shur2, and Stephen K. O’Leary1 1 School of Engineering, The University of British Columbia, Kelowna, British Columbia, Canada V1V 1V7 2 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, U.S.A. ABSTRACT Zinc oxide has recently been touted as a material that may prove useful for high-power and high-frequency electron device applications. Unfortunately, at the present moment at least, zinc oxide’s electron transport results are based upon material parameter selections that remain disputed, i.e., their exact values have yet to be satisfactorily resolved. In order to establish how the expected range of disputed material parameter values influence the corresponding electron transport results, this paper assesses the sensitivity of the electron transport results associated with zinc oxide to variations in these disputed material parameters. The disputed material parameters that we focus on for the purposes of this particular analysis include the nonparabolicity coefficient associated with the lowest energy conduction band valley, the conduction band inter-valley energy separation, and the effective mass associated with the electrons in the upper energy conduction band valleys. For the purposes of this analysis, steady-state electron transport results are the focus of this sensitivity analysis, the velocity-field characteristic associated with zinc oxide being the principal metric of concern. We find that increases in the non-parabolicity coefficient associated with the lowest energy conduction band valley lead to increases in the peak field of the velocity-field characteristic and initially an increase and then a decrease in the peak electron drift velocity of this material. Increases in the conduction band inter-valley energy separation are instead found to result in increases in the peak field and concomitant increases in the peak electron drift velocity. Finally, increases in the effective mass associated with the electrons in the upper energy conduction band valleys are found to lead to a sharpening of the slope of the velocity-field characteristic in the region beyond the peak field, greater effective mass leading to a greater magnitude slope. Based on the magnitude of these variations, we conclude that zinc oxide may indeed be considered as a material for high-power and high-frequency electron device applications even when the variations in these disputed material parameters have been accounted for. INTRODUCTION During the past two decades, semiconductors with wider energy gaps have become a focus of great interest. Amongst these wider energy gap semiconductors, zinc oxide (ZnO), a IIVI compound semiconductor, has drawn a considerable following in recent years. ZnO is in possession of an elevated polar optical phonon energy and a pronounced inter-valley energy separation [1]. This conjuncture of material properties suggests t
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