Composition modulation and inhomogeneous strain field in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/InP strained layers

Optical-absorption measurements have been carried out on tensile and compressive ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/InP strained layers. It is shown that the energetic dispersion of the heavy-hole relative to the light-hole subband ${\mathrm{\sigma }}_{\mathrm{HH}}$/${\mathrm{\sigma }}_{\mathrm{LH}}$ is the key to knowing the origin of the microscopic inhomogeneities. So, ${\mathrm{\sigma }}_{\mathrm{HH}}$/${\mathrm{\sigma }}_{\mathrm{LH}}$<1 indicates the existence of composition inhomogeneities whereas ${\mathrm{\sigma }}_{\mathrm{HH}}$/${\mathrm{\sigma }}_{\mathrm{LH}}$=2.8 reveals an inhomogeneous strain field.