Optical spectroscopic studies of N-related bands in Ga(N,As)

We have investigated the unusual band formation at the Gamma-point and in t he vicinity of the L-point in the alloy system Ga(N,As) by various spectros copic methods. A series of GaNxAs1-x epitaxial layers with x varying from 0 .05 to 2.8% was grown on (100) GaAs by metal-organic vapour phase epitaxy. The samples were studied by photoluminescence (PL) as well as photoluminesc ence excitation (PLE) spectroscopy, photomodulated reflectance (PR), and co nventional reflectance (R) spectroscopy at room temperature and liquid heli um temperature. The low-temperature PL and PLE spectra in the spectral regi on of the Eo band gap show clear evidence for in-gap nitrogen-pair and clus ter states at low concentrations (x < 0.1%), and for higher nitrogen concen trations the formation of a new band. The dependence of the E-0 band gap on N-content for x < 1% at-8 K is considerably stronger than at 300K. Further more, R spectra of the E-1 and E-1 + Delta(1) transitions show an uncommonl y strong disorder-induced broadening with increasing N-content.