Raman and dielectric function spectra of strained GaAs1-xSbx layers on InP

Raman spectroscopy and variable angle spectroscopic ellipsometry (SE) were used to study pseudomorphically strained GaAs1-xSbx layers (0.22 less than or equal to x less than or equal to 0.65) grown on InP by metal-organic che mical vapor deposition. From the Raman spectra the composition dependence o f the GaAs-like LO phonon mode was deduced. For comparison with literature data for unstrained GaAs1-xSbx, the strain-induced frequency shift of the G aAs-like LO phonon was calculated and subtracted from the present experimen tal data. When corrected for strain effects the composition dependent GaAs- like LO phonon frequency could be fitted by the linear relation omega(LO)=2 92.3-51x(cm(-1)) for the present range of alloy compositions. The pseudodie lectric function spectra, deduced from SE measurements covering the range o f photon energies from 0.8 to 5.0 eV, were fitted by a multilayer model emp loying a set of parametric oscillators to describe the GaAs1-xSbx dielectri c function. From the resulting parametric dielectric functions the composit ion dependence of the E-1 and E-1+Delta(1) critical point energies was dedu ced for pseudomorphically strained GaAs1-xSbx on InP and, after correction for strain effects on the interband transitions, also for unstrained GaAs1- xSbx. (C) 2000 American Institute of Physics. [S0021-8979(00)07712-4].