Characterisation of intrinsic and compensated defect microstructures in dilute III-V-N alloys

A comprehensive analysis of the Fourier transform infrared (FTIR) absorption and Raman scattering data on impurity modes is reported for the technologically important dilute ternary GaAs_1-xN_x, and GaP_1-xN_x (x<0.03) alloys grown on GaAs and GaP, respectively, by metal organic chemical vapour deposition (MOCVD) and solid source molecular beam epitaxy (MBE). For low nitrogen concentrations in GaAs_1-xN_x [GaP_1-xN_x] (i.e. x<0.015), most of the N atoms occupy the As [P] sublattice N_As [N_P]. They prefer, however, to move out of their substitutional sites to more energetically favourable locations at higher x values. To comprehend the large width of the localised vibrational mode (LVM) in GaAs_1-xN_x near 470 cm^-1, the possibilities of Ga isotopes (⁶⁹Ga and ⁷¹Ga) and/or intrinsic defects participating with N_As in different configurations were studied. Theoretical results for the N-local modes and its isotopic shifts are found in good agreement with the FTIR data. Although, the presence of isolated N-interstitials (N_int) in GaAs_1-xN_x is quite unlikely at higher compositions (0.03>x>0.015), the formations of nonradiative complex microstructures involving N and/or intrinsic defects are energetically favourable. The impurity modes for such complex centres were predicted and the possibility of observing them by optical spectroscopy was evaluated.