Unusual properties of metastable (Ga, In)(N,As) containing semiconductor structures

An overview is presented of experimental and theoretical work on band structure aspects of (Ga,In)(N,As) and Ga(N,As) quantum well structures and epitaxial layers grown by molecular beam epitaxy (MBE) and metal-organic vapour phase epitaxy (MOVPE). The evolution of unusual band structure and phonon features in GaN_xAs_1-x with increasing x caused by the impurity character of nitrogen in GaAs is discussed. Hydrogenation of Ga(N,As) allows one to virtually switch off the N-induced changes of the band structure and the vibrational modes. A strong blue shift up to about 100 meV of the bandgap of quaternary samples is observed on thermal annealing. The magnitude of the blue shift depends strongly on In and N concentrations as well as on the growth and annealing conditions. Raman spectra of MOVPE-grown (Ga,In)(N,As) epitaxial layers reveal local In-N and Ga-N modes. On annealing, the intensity ratios of the local modes change, indicating a rearrangement of the nitrogen nearest-neighbour environments from Ga-rich to In-rich environments. Tight binding calculations suggest that this might contribute strongly to the observed blue shift. Other possible contributions to the blue shift are also discussed.