Research on the epitaxial growth of Power/RF HEMT structures on n-GaN and Fe-doped SI-GaN Free-Standing Substrates by MOCVD

Abstract

This paper systematically studies the epitaxial growth of Power and Radio Frequency (RF) AlGaN/GaN high-electron-mobility transistors (HEMTs) on Free-Standing GaN substrates using Metal-Organic Chemical Vapor Deposition (MOCVD). In the Power HEMT epitaxial layer grown on n-GaN substrate, a uniform incorporation of carbon (C) dopants with a concentration of 5 × 10¹⁸/cm³ into the GaN buffer layer was achieved through low-temperature growth without degrading the crystal quality. Compared to sapphire-based samples, the dislocation density of HEMT epitaxial layers on the Free-Standing substrate decreased from 2.4 × 10⁹/cm² to 2.1 × 10⁷/cm², while the surface roughness was reduced from 0.407 nm to 0.161 nm. Additionally, the two-dimensional electron gas (2DEG) concentration increased by 30 %, with a mobility of 2209 cm²/V·s, and a record-breaking low-temperature mobility of 9510 cm²/V·s at 94K. Furthermore, in the RF HEMT epitaxial structure grown on Fe-doped semi-insulating GaN (SI-GaN) substrate. The introduction of a Fe-diffusion stopper layer effectively suppressed the memory effect of Fe and reduced the Fe impurity concentration in the GaN channel layer from 8.2 × 10¹⁷/cm³ to 9.6 × 10¹⁶/cm³ within a few nanometers, significantly improving the 2DEG performance.