Preferential formation of Al-N bonds in low N-content AlGaAsN

The bonding of nitrogen in low N-content AlxGa1-xAs1-yNy with xless than or equal to0.05 and yless than or equal to0.04 has been studied by Raman spectroscopy. Upon the addition of Al to GaAsN, additional vibrational modes are observed at around 450 cm(-1), which is below the GaN-like longitudinal optical (LO) phonon mode centered at 470 cm(-1). These modes are attributed to the formation of Al and N containing complexes with Al-to-N bonding. With increasing Al content the Al-N related modes gain intensity at the expense of the GaN-like mode, and they become the dominant N-related feature for an Al-content of 5% at a fixed N content of 1%. On the other hand, increasing the N content from 0% up to 4% at a constant Al concentration of 5% results first in the appearance and eventual saturation in intensity of the AlN-like modes, accompanied by a steep increase in intensity and eventual dominance of the GaN-like vibrational mode. Simultaneously the AlAs-like LO2 phonon mode shows a drastic decrease in intensity for N contents exceeding 2%. All these observations strongly indicate that there is a preferential formation of Al-N bonds in low N- and Al-content AlGaAsN, which is in direct contrast to GaInAsN, where even after thermal annealing the GaN-like mode remains dominant in the Raman spectrum compared to the InN-like modes. (C) 2002 American Institute of Physics.