PROPERTIES OF MOLECULAR-BEAM EPITAXY-GROWN GANAS FROM OPTICAL SPECTROSCOPY

GaNxAs1-x layers with different nitrogen concentrations x grown on (00 1)GaAs substrates by molecular-beam epitaxy have been studied by photo luminescence, optical absorption, and Raman spectroscopy. The content of nitrogen in the layers was determined by x-ray diffraction and seco ndary-ion-mass spectrometry. The samples can be classified in three ca tegories with respect to the concentration of N: with doping nitrogen concentration, with average content of N less than 0.3, and with x clo se to 1. From optical measurements and from analysis of x-ray diffract ion spectra, different phases are observed in the GaNxAs1-x layers: Ga As, GaN, and the solid ternary solution GaNxAs1-x. In Raman spectra bo th GaAs-like and GaN-like optical phonons are observed. We have estima ted the fundamental band-gap energy in the GaNxAs1-x alloy with low ni trogen concentration up to x=0.04 from absorption measurements, and in GaNxAs1-x with high nitrogen concentration x>0.96 from photoluminesce nce spectra. Fitting of the experimental data for low x values gives a constant bowing parameter as big as b=-18 eV. This value predicts the band-gap energy for the high nitrogen concentration in agreement with experimental data. Consequently, GaNxAs1-x is predicted to be semimet allic in the range 0.12<x<0.75. (C) 1998 American Institute of Physics . [S0021-8979(98)00819-6].