Magneto-optical studies of strain effects on the excitons in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As strained quantum wells

Low-temperature (4.2 K) magnetoreflectance measurements have been performed on a series of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As strained-layer quantum wells (QW’s) with the InAs mole fraction x varying from 0 to 0.2, for three different well widths, and for the magnetic-field range of 0–9 T. The diamagnetic shift data of 1s, 2s, 3s,... excitons are fit to a theoretical model to determine the exciton binding energies and the in-plane reduced effective masses, which are presented as a function of x, for excitons in 80, 120, and 340 Å ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As QW’s. In the case of high-barrier QW’s, the binding energies and effective masses appear to decrease linearly with increasing x over the range studied. The rate of change of the effective mass μ as x increases from 0 to 0.2 is experimentally determined, using two different methods, to be dμ/dx=-0.057${\mathit{m}}_0$ and dμ/dx=-0.041${\mathit{m}}_0$, which exhibits a substantial strain dependence when compared with the value dμ/dx=-0.07${\mathit{m}}_0$, from unstrained bulk ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As. A theoretical approach taking into account the effect of composition change in the QW and strain on both the conduction and valence bands is made and gives dμ/dx=-0.051${\mathit{m}}_0$, which is in good agreement with our experimental result.