GaN HEMT with improved electrical performance enabled by hybrid AlN nucleation layers

Abstract

Herein, a 1.8-μm GaN-on-sapphire high-electron-mobility transistor (HEMT) with superior crystal quality is developed by elaborately modulating the initial nucleation stage of the hybrid AlN nucleation layers (NLs), including both a 25-nm magnetron sputtered AlN and a 60-nm metalorganic-chemical-vapor-deposition-grown AlN (MO-AlN). The hybrid AlN-NL, subjected to an additional in situ thermal annealing process in an H2 atmosphere, not only offers nucleation sites for subsequent HEMT epitaxy but also benefits dislocation annihilation in a GaN buffer with scaled-down thickness. The as-grown GaN buffer layer of the HEMT structure features the full-width-half-maximum values as low as 53 and 179 arc sec for (002) and (102) x-ray rocking curves diffractions, which are among the best crystalline qualities of the (ultra)thin-GaN-buffer structures on sapphire substrates. The as-grown 4-in. HEMT epitaxial layer exhibits a uniform sheet resistance of 309 Ω/□ across the wafer with a 2DEG concentration of 1 × 1013 cm−2 and an electron mobility exceeding 2000 cm2/(V s), serving as a promising platform for the fabrication of GaN HEMTs for power electronics applications.