Corona discharge supersonic free-jet for III–V nitride growth via A 3Σu+ metastable nitrogen molecules

A corona discharge supersonic free-jet is shown to be a nearly pure source of A 3Σu+ metastable molecular nitrogen, an electronically excited and chemically active form of N2 that is ideally suited to nitride semiconductor growth. Optical emission spectroscopy at various distances downstream of the supersonic nozzle reveals a cascade through the excited state manifold of N2 triplet states to populate the A 3Σu+ state. Appearance potential spectroscopy (mass spectrometer electron bombardment ionization yield, measured as a function of electron impact energy) delivers the composition of the terminal molecular beam. A 3Σu+ molecules are the dominant activated species in the beam, which otherwise contains only nonreactive X 1Σg+ ground state nitrogen molecules plus a minor amount of S04 nitrogen atoms. Up to 1.56% number fraction of the beam is A 3Σu+, providing 1.0×1017 metastables sr−1 s−1.