OPTICAL STUDY OF VALENCE-BAND SPLITTING IN WEAKLY STRAINED IN1-XGAXASYP1-Y INP HETEROSTRUCTURES/

Valence band splitting resulting from strain epsilon approximate to 10 (-3) or less is observed in electroabsorption spectra of quaternary LP E material grown on (001) InP. Although exciton lines are not resolved their contribution leads to narrow, near-gap features in electroabsor ption which provides the necessary spectral resolution. The variation of lineshape with dc bias, temperature, and strain is studied in detai l. Small fields and low temperature are required to resolve splitting by a few meV. Even if linewidth broadening prevents resolution of vale nce band splitting, strain is evident by characteristic distortion of the spectral lineshape, different for compressive and tensile strain. Small splitting is resolved in case of tensile strain but not for comp ressive strain. This difference is attributed to stronger coupling of the valence bands for compressive strain where calculations show anti- crossing for dispersion in the layer plane.