III-N semiconductor growth with activated nitrogen: State-specific study of A³Σ⁺_u metastable N₂ molecules

High quality epitaxial III-N semiconductor films, ranging in thickness from 300 to 900 Å, have been grown using A³Σ⁺_u metastable nitrogen molecules. The work employed a corona discharge supersonic free-jet to generate a molecular beam containing exclusively the A³Σ⁺_u activation state in an otherwise ground state N₂ beam. AlN films were grown on 6H-SiC(0001) and Si(001) substrates. GaN films were grown on the same substrates and on buffer layers of AlN deposited in situ on 6H-SiC(0001). The N-atom incorporation efficiency (the number of N atoms attaching to a III-N surface per incident A³Σ⁺_u molecule) approached 100% and was independent of substrate temperature from 600 to 900°C, implying direct molecular chemisorption of the A³Σ⁺_u. These measurements support theoretical predictions that A³Σ⁺_u is an ideal precursor for III-N growth.