Gas-source molecular-beam epitaxial growth and optical characterization of AlxGa1-xP (0 <= x <= 78) alloy films

A series of AlxGa1-xP (0 less than or equal to x less than or equal to 0.78) alloy films has been grown on S-doped GaP(001) substrates by using gas-source molecular-beam epitaxy with elemental Ga and Al, and P-2 cracked from PH3 as the source materials. The Al composition and the crystalline quality of the samples were determined by double-crystal X-ray diffraction measurements. The vibrational properties of the alloys were examined by Raman spectroscopy, and the measured spectra exhibited GaP-LO and "AlP-like" LO phonon peaks. The "AlP-like" LO phonon peak showed a strong compositional dependence. A spectroscopic ellipsometric measurement was also performed to determine the quality of the films.