Flexible Gallium Nitride for High-Performance, Strainable Radio-Frequency Devices

Flexible gallium nitride (GaN) thin films can enable future strainable and conformal devices for transmission of radio-frequency (RF) signals over large distances for more efficient wireless communication. For the first time, strainable high-frequency RF GaN devices are demonstrated, whose exceptional performance is enabled by epitaxial growth on 2D boron nitride for chemical-free transfer to a soft, flexible substrate. The AlGaN/GaN heterostructures transferred to flexible substrates are uniaxially strained up to 0.85% and reveal near state-of-the-art values for electrical performance, with electron mobility exceeding 2000 cm² V^-1 s^-1 and sheet carrier density above 1.07 × 10¹³ cm^-2 . The influence of strain on the RF performance of flexible GaN high-electron-mobility transistor (HEMT) devices is evaluated, demonstrating cutoff frequencies and maximum oscillation frequencies greater than 42 and 74 GHz, respectively, at up to 0.43% strain, representing a significant advancement toward conformal, highly integrated electronic materials for RF applications.

Incomplete Ionization of a 110 meV Unintentional Donor in β-Ga2O3 and its Effect on Power Devices

Understanding the origin of unintentional doping in Ga₂O₃ is key to increasing breakdown voltages of Ga₂O₃ based power devices. Therefore, transport and capacitance spectroscopy studies have been performed to better understand the origin of unintentional doping in Ga₂O₃. Previously unobserved unintentional donors in commercially available \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\bar{2}01)$$\end{document}(2¯01) Ga₂O₃ substrates have been electrically characterized via temperature dependent Hall effect measurements up to 1000 K and found to have a donor energy of 110 meV. The existence of the unintentional donor is confirmed by temperature dependent admittance spectroscopy, with an activation energy of 131 meV determined via that technique, in agreement with Hall effect measurements. With the concentration of this donor determined to be in the mid to high 10¹⁶ cm⁻³ range, elimination of this donor from the drift layer of Ga₂O₃ power electronics devices will be key to pushing the limits of device performance. Indeed, analytical assessment of the specific on-resistance (R_onsp) and breakdown voltage of Schottky diodes containing the 110 meV donor indicates that incomplete ionization increases R_onsp and decreases breakdown voltage as compared to Ga₂O₃ Schottky diodes containing only the shallow donor. The reduced performance due to incomplete ionization occurs in addition to the usual tradeoff between R_onsp and breakdown voltage.