The electron transport within bulk wurtzite zinc oxide in response to strong applied electric field pulses
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The electron transport within bulk wurtzite zinc oxide in response to strong applied electric field pulses Walid A. Hadi1, Michael S. Shur2, and Stephen K. O’Leary3 1
Department of Electrical and Computer Engineering, University of Windsor, Windsor, Ontario, Canada N9B 3P4 2 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, U.S.A. 3 School of Engineering, The University of British Columbia, Kelowna, British Columbia, Canada V1V 1V7 ABSTRACT Strong short electric field pulses are used to generate broadband terahertz radiation. Understanding the transport properties under such conditions is very important for the understanding of numerous terahertz photonic and electronic devices. In this paper, we report on transport simulations of the electrons within bulk wurtzite zinc oxide for pulsed high electric fields, with pulse durations of up to 400 fs. We focus on how key electron transport characteristics, namely the drift velocity and the corresponding average energy, vary with time since the onset of the pulse. For sufficiently high-field strength selections, we find that both of these parameters exhibit peaks. In addition, an electron drift velocity undershoot is observed following this peak. A contrast with the case of gallium nitride is considered; undershoot is not observed for the case of this material. Reasons for these differences in behavior are suggested. INTRODUCTION In recent years, the II-VI semiconductor, zinc oxide (ZnO), has generated a great amount of interest [1]. ZnO’s energy gap is comparable to that exhibited by gallium nitride (GaN) [2]. This suggests that high-field electron device architectures currently in use, or envisaged, for GaN may also be considered for ZnO. The electron transport that occurs within ZnO has been extensively examined, these studies suggesting that the electrons within wurtzite ZnO exhibit pronounced steady-state drift velocities and significant velocity overshoot [3-10]. This further adds to the allure of ZnO as a potential material for future high-field electron device applications. In this paper, we examine how electrons within bulk wurtzite ZnO move in response strong electric field pulses. Electron transport simulations are employed for this analysis. Pulse durations of up to 400 fs in duration are considered. We principally focus on how key electron transport characteristics, namely the drift velocity and the corresponding average energy, vary with time since the onset of the pulse. From this analysis, a preliminary characterization of the electric field pulse response of the electrons within wurtzite ZnO will be performed.
SIMULATIONS We follow a course of analysis paralleling that employed earlier by O’Leary et al. [7] and Hadi et al. [8, 9]. The results presented here are obtained from ensemble semi-classical threevalley Monte Carlo simulations of the electron transport that occurs within bulk wurtzite ZnO. Ionized impurity, polar optical phonon, piezoelectric, and acoustic deformation potenti
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