RAMAN INVESTIGATION OF MOLECULAR-BEAM EPITAXY-GROWN INGAALAS EPILAYERS LATTICE-MATCHED TO INP FOR LOW AL CONCENTRATIONS

Room temperature Raman measurements on a series of molecular beam epit axy grown In0.53Ga0.47-xAlxAs epilayers lattice matched to InP substra tes have been carried out for the composition range 0 less than or equ al to x less than or equal to 0.08. This low Al composition range is i mportant for tailoring the well gap energy in communication device fab rication. The Raman data show three-mode phonon behavior for films wit h Al concentrations as low as x=0.03. In addition to detecting the fun damental one-phonon scattering processes, overtone, and combinations o f the GaAs-like and AlAs-like optic phonon modes are recorded. These a re then used to determine the composition dependent phonon mode shifts . By comparing the separate estimates of the free carrier band-gap ene rgy using low temperature absorption and photoluminescence measurement s, unintentional doping of the epilayers by the substrate is revealed. (C) 1998 American Institute of Physics.