Effect of Carrier Gas on Silicon Doped GaN Epilayer Characteristics

Abstract

Heavily Si-doped GaN epitaxial layers (n⁺GaN) have been grown on semi-insulating 6H-SiC substrate by metal–organic chemical vapor deposition at 1030°C using H₂ and N₂ as carrier gases. Thin film characterization results demonstrated that n⁺GaN grown in N₂ carrier gas has superior morphological and crystalline quality to that grown in H₂. The surface morphology of n⁺GaN grown with N₂ carrier gas is insensitive to the growth rate and SiH₄ flow with Si doping concentration up to 1.1 × 10²⁰/cm³. Secondary ion mass spectrometry analysis confirmed that C and O impurity levels in n⁺GaN are one order of magnitude lower with N₂ carrier gas than with H₂. The results thus indicate that 100% N₂ could be a better carrier gas candidate to enable a broader process window for future HEMT S/D n⁺GaN selective area epitaxial process applications.