Electron transport within a zinc-oxide-based two-dimensional electron gas: The impact of variations in the electron effe
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Electron transport within a zinc-oxide-based two-dimensional electron gas: The impact of variations in the electron effective mass Walid A. Hadi1, Erfan Baghani2, Michael S. Shur3, and Stephen K. O’Leary2 1
Department of Electrical and Computer Engineering, University of Windsor, Windsor, Ontario, Canada N9B 3P4 2 School of Engineering, The University of British Columbia, Kelowna, British Columbia, Canada V1V 1V7 3 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, U.S.A. ABSTRACT We examine the electron transport that occurs within a zinc-oxide-based two-dimensional electron gas using Monte Carlo simulations. The sensitivity of the results to variations in the lowest energy conduction band valley electron effective mass is examined. Increased values of the electron effective mass result in diminished electron drift velocities and reduced sensitivity to the free electron concentration. In agreement with our previous studies for a fixed value of the electron effective mass [11], we find that the reduced scattering due to the screening of the impurity and polar optical scattering leads to a slightly higher mobility of the 2DEG at low-fields but reduces the peak velocity, since gaining a higher energy due to the reduced polar optical phonon scattering enhances the effects of the non-parabolicity within this material. INTRODUCTION Most studies of the electron transport within ZnO focus on the bulk material [1-7]. It is widely recognized, however, that the electron transport within an actual device differs from that within the bulk, these differences arising from the inhomogeneities that one encounters within an actual device. Experimental measurements by Tampo et al. [8], for example, point to a dramatic enhancement in the low-field electron mobility in the vicinity of a ZnO/ZnMgO heterojunction, thus suggesting the presence of a two-dimensional electron gas there. This result suggests that ZnO-based high electron mobility transistors, based on a heterostructure of ZnO with ZnMgO, can be realized. More recent analyzes, such as that by Akasaka et al. [9], confirm this observation; a review of recent results is provided by Tsukazaki et al. [10]. In order to properly design such a transistor, a clear understanding of the nature of the electron transport within a ZnO-based two-dimensional electron gas must be acquired. Hadi et al. [11], noting that the free electron concentration within a two-dimensional electron gas is substantially greater than the corresponding ionized impurity concentration, employ Monte Carlo simulations of the electron transport within ZnO for which the free electron concentration is enhanced beyond the ionized donor impurity concentration in order to simulate the nature of the electron transport within a ZnO-based two-dimensional electron gas. They find that at highfields, increases in the free electron concentration result in a decrease in the corresponding electron drift velocity. In this paper, we will continue to examine the
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