Origin of proton irradiation-induced deep acceptors in Al0.70Ga0.30N

Abstract

Deep level defect introduction and carrier removal were characterized using steady-state photocapacitance (SSPC), deep level transient spectroscopy (DLTS) and lighted capacitance–voltage for proton irradiated n-type Al0.70Ga0.30N Schottky diodes grown by metal-organic vapor phase epitaxy on AlN-on-sapphire templates. SSPC observed deep levels in the as-grown diode with zero-phonon transition energies of 2.20, 2.65, 3.10, 3.40, and 4.65 eV relative to the conduction band minimum (Ec), and an additional deep level emerged at 1.20 eV with irradiation. Lighted capacitance–voltage measurements quantified the deep level concentration (Nt) of states detected by SSPC, and it was observed that Nt increased with proton fluence only for the 1.2 and 4.65 eV levels. Carrier removal was much larger than the increase in Nt of the 1.2 and 4.65 eV deep levels, suggesting that radiation-induced deep level compensators existed beyond what was detected with SSPC. DLTS detected additional, proton-induced deep acceptors at Ec—0.55, 0.82, and 1.16 eV, the latter of which is likely the same 1.20 eV deep state observed by SSPC. The concentration of the Ec—0.82 eV defect state was large enough to reconcile carrier removal with total deep level introduction. Comparing the Ec—0.82 and 1.16 eV deep acceptor levels to previous experimental and theoretical reports suggests that their atomistic origins could be the nitrogen vacancy (VN) and oxygen substituting on the nitrogen sub-lattice (ON), respectively. This defect behavior contrasts starkly with GaN, where VN and ON are shallow donors, and demonstrates that the electronic properties of defects can evolve drastically within the AlGaN alloy system ranging from wide bandgap GaN to ultra-wide bandgap AlN.