Deep-level point defects at Ga sites in dilute AlxGa1<b>−</b> <i>x</i>N alloys

Abstract

Deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS (L-DLTS) have been applied for studying electron traps in Si-doped dilute AlxGa1−xN films (0 ≤ x ≤ 0.063), grown by metal-organic vapor phase epitaxy on Ammono-GaN substrates. Two electron emission signals have been detected in DLTS spectra of all AlxGa1−xN samples and the activation energy for electron emission relative to the conduction band edge (EC) from the first level shifts from EC–0.25 to EC–0.34 eV and that for the second level shifts from EC–0.6 to EC–0.68 eV upon changes of x from 0 to 0.063. In the L-DLTS spectra of the Al0.063Ga0.937N samples, the electron emission signals associated with the EC–0.34 eV donor and EC–0.68 eV acceptor levels split into individual components due to aluminum fluctuations in the nearest neighbor (NN) shells. The splitting patterns are nearly identical for both signals and the ratios of peak magnitudes are consistent with calculated probabilities of finding a given number of aluminum atoms in the second NN shell around a Ga lattice site. These findings provide strong evidence that the EC–0.34 and EC–0.68 eV trap states in Al0.063Ga0.937N are related to point defects in the Ga sub-lattice. Finally, a comprehensive scan of possible impurities and defect levels in GaN and AlxGa1−xN using first-principles calculations suggests that the EC–(0.25–0.34) eV electron trap in AlxGa1−xN (0 ≤ x ≤ 0.063) is most likely related to carbon or molybdenum donor states, specifically, CGa(0/+) or MoGa(0/+).