Increasing the mobility and power-electronics figure of merit of AlGaN with atomically thin AlN/GaN digital-alloy superlattices

Abstract

Alloy scattering in random AlGaN alloys drastically reduces the electron mobility and, therefore, the power-electronics figure of merit. As a result, Al compositions greater than 75% are required to obtain even a twofold increase in the Baliga figure of merit compared to GaN. However, beyond approximately 80% Al composition, donors in AlGaN undergo the DX transition, which makes impurity doping increasingly more difficult. Moreover, the contact resistance increases exponentially with the increase in Al content, and integration with dielectrics becomes difficult due to the upward shift of the conduction band. Atomically thin superlattices of AlN and GaN, also known as digital alloys, are known to grow experimentally under appropriate growth conditions. These chemically ordered nanostructures could offer significantly enhanced figure of merit compared to their random alloy counterparts due to the absence of alloy scattering, as well as better integration with contact metals and dielectrics. In this work, we investigate the electronic structure and phonon-limited electron mobility of atomically thin AlN/GaN digital-alloy superlattices using first-principles calculations based on density-functional and many-body perturbation theory. The bandgap of the atomically thin superlattices reaches 4.8 eV, and the in-plane (out-of-plane) mobility is 369 (452) cm2 V−1 s−1. Using the modified Baliga figure of merit that accounts for the dopant ionization energy, we demonstrate that atomically thin AlN/GaN superlattices with a monolayer sublattice periodicity have the highest modified Baliga figure of merit among several technologically relevant ultra-wide bandgap materials, including random AlGaN, [Formula: see text]-Ga2O3, cBN, and diamond.

Interfacial Distortion of Sb2Te3–Sb2Se3 Multilayers via Atomic Layer Deposition for Enhanced Thermoelectric Properties

“…The Hall mobility of the systems falls within the range of 90–120 cm 2 V –1 s –1 , which is lower than a value of 140 cm 2 V –1 s –1 observed in the Sb 2 Te 3 layer (Figure c). Interface scattering arises when carriers traverse between different layers, leading to mobility restrictions and impacting overall mobility . Additionally, potential barriers within the superlattice structure can obstruct the interlayer transport of charge carriers, further reducing mobility .…”

“…Interface scattering arises when carriers traverse between different layers, leading to mobility restrictions and impacting overall mobility. 25 Additionally, potential barriers within the superlattice structure can obstruct the interlayer transport of charge carriers, further reducing mobility. 26 Furthermore, interface effects can induce the formation of interface states, which act as scattering centers for carriers, contributing to additional charge scattering and a subsequent decrease in mobility.…”

GaN-based power high-electron-mobility transistors on Si substrates: from materials to devices

“…Compared to these nucleation layers, the AlN interlayer as nucleation layer has been widely applied, for the following reasons. First, AlN (α = 0.3112 nm) has a smaller lattice constant than GaN (α = 0.3189 nm), which theoretically yields a lattice mismatch between AlN and GaN of 2.6%, which amounts to a compressive stress of more than 11 GPa [63]. The compressive stress is considerably larger than that required to compensate for the tensile stress generated by the thermal mismatch between GaN and Si [64] (∼1.5 GPa), which offsets the tensile growth and thermal stress in the growth of the GaN-on-Si substrates [65].…”

A Modeling Study of Electron Transport in GaN/AlGaN Superlattices Using Monte Carlo Simulation

“…Compared with other simulations of SL electron transport, this work also shows a certain consistency. Nick et al [ 40 ] utilized the electron–phonon Wannier method to solve the linear Boltzmann transport equation for 2MLs, reporting electron mobility of 220 cm 2 (V s) −1 . This corresponds to an electron velocity of approximately 2.2 × 10 7 cm s −1 at 100 kV cm −1 and 4.4 × 10 7 cm s −1 at 200 kV cm −1 .…”