Optical Spectroscopic Studies of N-Related Bands in Ga(N,As)

We have investigated the unusual band formation at the Γ-point and in the vicinity of the L-point in the alloy system Ga(N, As) by various spectroscopic 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 photoluminescence excitation (PLE) spectroscopy, photomodulated reflectance (PR), and conventional reflectance (R) spectroscopy at room temperature and liquid helium temperature. The low-temperature PL and PLE spectra in the spectral region of the E0 band gap show clear evidence for in-gap nitrogen-pair and cluster states at low concentrations (x < 0.1%), and for higher nitrogen concentrations the formation of a new band. The dependence of the E0 band gap on N-content for x < 1% at 8 K is considerably stronger than at 300 K. Furthermore, R spectra of the E1 and E1 + Δ1 transitions show an uncommonly strong disorder-induced broadening with increasing N-content.