STUDY OF STRAIN AND DISORDER OF INXGA1-XP (GAAS, GRADED GAP) (0.25-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.8) USING SPECTROSCOPIC ELLIPSOMETRY AND RAMAN-SPECTROSCOPY

The optical properties of InxGa1-xP/GaAs and InxGa1-xP/graded InGaP/GaP (0.25 less-than-or-equal-to x less-than-or-equal-to 0.8 epitaxial layers have been studied using spectroscopic ellipsometry and Raman spectroscopy. The (E1,E1 + DELTA1) critical points and the first-order phonon frequencies were determined as a function of In composition. The general behavior of the peak shifts and broadenings of both the E1 gaps and the optical phonons of InxGa1-xP/GaAs can be explained in terms of biaxial strain and strain relaxation caused by lattice-mismatch. The near-cancellation of E1 gap change due to the compensation effect between alloy composition and misfit strain is observed. As misfit strain increases, the E1 gap broadens whereas the phonon line shape does not change. In strain relaxed samples of InxGa1-xP/(GaAs, graded GaP) (0.3 less-than-or-equal-to x less-than-or-equal-to 0.8), the E1 gap linewidth shows upward bowing as a function of In composition.