Electron mobility influenced by optical phonons in AlGaN/GaN MISHEMTs with different gate dielectrics
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Electron mobility influenced by optical phonons in AlGaN/GaN MISHEMTs with different gate dielectrics Xiaojuan Zhou1,2 · Zhiping Wang1 · Yuan Qu1 · Shiliang Ban1 Received: 18 May 2020 / Accepted: 17 September 2020 / Published online: 1 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The electron mobility influenced by optical phonons in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with different gate dielectrics around room temperature is investigated theoretically. The electronic states are obtained by the finite difference method in consideration of built-in electric fields and the conduction band bending. The optical phonons are analyzed using the dielectric continuum model. Based on the theory of force balance equation, the electron mobility of two-dimensional electron gas is obtained for the structures with four different gate dielectrics of A l 2O 3, HfO2, SiO2 and Si3N4. Our results show that the electron mobility is the highest in H fO2 systems when Al composition in AlGaN is small, whereas the mobility is the highest in A l2O3 systems as Al composition increases to a certain value. The effects of the ternary mixed crystals, each layer’s size and the fixed charges on the sheet density and electron mobility are also discussed for different gate dielectric materials. Keywords Electron mobility · Optical phonon · Metal-insulator-semiconductor high electron mobility transistor · Gate dielectric
1 Introduction Metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) based on AlGaN/GaN heterostructures have been attracting much attention because they can effectively reduce the leakage current and suppress the current collapse effect [1, 2]. The density and mobility of two-dimensional electron gas (2DEG) determine the performances of the transistors. Many theoretical studies analyzed the possible scattering mechanisms limiting the electron mobility in these devices. The results showed that in an insulator/semiconductor system, the electrons in the semiconductor suffer the scattering from surface phonons or remote phonons when they are close to the insulator [3, 4]. The electron mobility in metal-oxide-semiconductor field effect transistors can be reduced by the remote scattering * Shiliang Ban [email protected] 1
Department of Physics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
Ordos Institute of Applied Technology, Ordos 017000, Inner Mongolia, China
2
from insulator-phonons [5–9]. However, this scattering in AlGaN/GaN MISHEMTs is negligible because there is at least one barrier layer between the insulator and 2DEG. Ridley pointed out that the scattering mechanisms in high electron mobility transistors mainly include acoustic and optical phonons, alloy disorder, etc. [10]. Later on, it was shown that optical-phonon scattering is dominant in AlGaN/ GaN heterostructures with high density 2DEG around room temperature [11, 12]. The dielectric-continuum (DC) model ca
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