Photoreflectance spectroscopy of electron-hole states in a graded-width GaAs/InGaAs/GaAs quantum well

The spectrum of electron-hole states in a GaAs/In$_{0.5}$Ga$_{0.5}$As quantum well with a width graded in the range from 1.1 to 3.6 nm is studied by photoreflectance spectroscopy. The energies of the size-quantization levels of electrons and holes are calculated taking into account the strain-induced changes in the band structures of the quantum well. It is shown that the best fit of the experimental data to the results of calculations is attained if the ratio between the offset of the conduction band and that of the valence band at the heterojunction is $Q=\Delta E_c/\Delta E_v$ = 0.62/0.38. A photoreflectance signal is detected in the region of the shadow of modulating radiation beam at a spacing between the spots produced by probing and modulating radiation shorter than 6 mm.