Intrinsically limited mobility of the two-dimensional electron gas in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures

Abstract

We report on the intrinsically limited low-field mobility of the two-dimensional electron gas (2DEG) in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures. Monte Carlo transport simulations are carried out to calculate the room-temperature 2DEG mobilities in dependence on the electron sheet density. The simulated 2DEG mobilities are compared to the phonon-limited mobility of bulk GaN. We estimate a maximum 2DEG mobility of about 2700 cm2 V−1 s−1 for an electron sheet density of ∼5×1012 cm−2, which remarkably exceeds the phonon-limited bulk mobility of 1520 cm2 V−1 s−1. By reducing the electron sheet density below 5×1012 cm−2, i.e., in a weak electron quantum confinement regime, the room-temperature 2DEG mobility gradually decreases and approaches the phonon-limited bulk value for vanishing quantum confinement. The insertion of a thin AlN barrier interlayer improves transport properties of the 2DEG and the mobility substantially increases due to a suppression of the alloy scattering.

Impact of Al content on transport properties of two-dimensional electron gas in GaN/AlxGa1−xN/GaN heterostructures

“…8,9 Recently, we have assessed the intrinsically limited mobility in gated defect-free AlGaN/GaN heterostructures. 10 In the present work, we expand our mobility analysis by accounting for, in addition to unavoidable intrinsic phonon and alloy scattering, also interface roughness and dislocation scattering. The calculated mobilities are then compared to the measured data.…”

A 2015 perspective on the nature of the steady-state and transient electron transport within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide: a critical and retrospective review

“…In 2003, Sevik and Bulutay [275] studied hot-electron effects within GaN/AlGaN-based devices using Monte Carlo simulations of the electron transport, a portion of this electron transport corresponding to the specific case of the electron transport within AlN itself. Other research results, related to the electron transport within AlN, or alloys with AlN, have also been reported, and are further discussed in the scientific literature [147,161,276,277].…”

Polarization Coulomb field scattering in AlGaN/AlN/GaN heterostructure field-effect transistors

“…3,4 The insertion of a thin AlN barrier interlayer improves transport properties of the two-dimensional electron gas ͑2DEG͒ and the mobility substantially increases due to a suppression of the alloy scattering. 5 The polarization Coulomb field scattering related to the strain variation in the AlGaN barrier layer has an important influence on the 2DEG electron mobility in the circular AlGaN/GaN HFET devices. 6 Since the strained AlGaN/AlN/GaN heterostructures have been the popular material structure for AlGaN/GaN HFETs, and the rectangular AlGaN/GaN HFETs are the main-stream Gallium nitridebased devices for microwave and high power applications, it is important to understand the role that the polarization Coulomb field scattering plays in the rectangular AlGaN/AlN/ GaN HFET devices.…”

“…This is attributed to the AlN interlayer in the strained AlGaN/AlN/GaN heterostructures to enlarge the average distance between the 2DEG electrons and the polarization charges which generate the polarization Coulomb field. 5,6 With the AlN interlayer, the conduction band discontinuity ⌬E C at the AlN/GaN interface is larger than that at the AlGaN/GaN interface. The penetration of the 2DEG electron wave function into the AlGaN barrier layer is restrained and reduced.…”

“…The penetration of the 2DEG electron wave function into the AlGaN barrier layer is restrained and reduced. 5 As a result, the average distance between the 2DEG electrons and the polarization charges is enlarged even if the AlN interlayer is only 0.5 nm. 11 Thus, the polarization Coulomb field scattering is relatively weaker in the strained AlGaN/AlN/GaN heterostructures compared to that in the strained AlGaN/GaN heterostructures.…”