All three strainhyphen; and spinhyphen;orbithyphen;split energy gaps of the Ggr;15vhyphen;Ggr;1cseries are measured for the first time for a thin, strained Ga0.526In0.474As layer by a combination of transmission, photoreflectance (PR), and photoluminescence experiments at 10 and 300 K. Values of strain and composition of the layer are calculated from the splitting of the (J=3/2,mj=plusmn;3/2) and (3/2, plusmn;1/2) valence bands and from xhyphen;ray data. Force balance calculations predict the strain in the layer to be relaxed while energy balance calculations predict the layer to be strained. The onset of generation of misfit dislocations at the InP/GaInAs interface has recently been reported to be well described by the force balance model. Nevertheless, the data reported in the present study show the degree of plastic strain relaxation for the sample under investigation to be so small that it can be neglected for the interpretation of the optical spectra. Almost identical PR spectra are measured when the sample is excited at photon energies larger and smaller than the InP band gap. In both cases, the PR signal originates from modulation of built in fields at the heterointerfaces, rather than the surface field.
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