Epitaxial growth of a high-quality GaN/AlN heterostructure for the development of an AlN-back barrier high-electron-mobility-transistor

Abstract

AlN-back-barrier high electron mobility transistors (HEMTs) feature ultra-thin GaN channel layers grown on an AlN back barrier, thereby showing great promise in high-voltage, high-frequency applications. However, the growth mode of the thin GaN channel layer needs to be appropriately adjusted owing to the strong lattice and thermal mismatch between GaN and AlN. In this work, a two-step growth approach comprising low temperature (LT) and high temperature (HT) GaN layers was employed to achieve a balance between the crystal quality and surface morphology of the GaN channel layer by carefully varying the V/III ratio, pressure, and GaN thickness. The linewidths of the (002) and (102) XRD rocking curve diffractions as low as 180 and 309 arcsec, respectively, were obtained for a thin GaN channel layer of less than 600 nm. A significant reduction in dislocation density in GaN and a sharp GaN/AlN interface were revealed through transmission electron microscopy analysis. The correlation between the thickness of the GaN channel layer and the electrical properties of the AlN-back-barrier HEMT was established. A carrier concentration of 1.12 × 10¹³ cm⁻², Hall mobility of 1880 cm² V⁻¹ s⁻¹ and sheet resistance of 297.3 Ω sq⁻¹ were obtained, offering significant promise towards the development of high-performance HEMT devices.