Photomodulated transmission spectroscopy of the intersubband transitions in strained ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$As/GaAs multiple quantum wells under hydrostatic pressure

We report the measurement of the dependence of intersubband transitions on pressure for strained ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs multiple quantum wells with different indium concentrations and different well widths with photomodulated transmission spectroscopy. The spectral features associated with the transitions between the heavy-hole, light-hole states and the confined-electron states have been found to shift towards higher energy with pressure in a manner similar to the pressure dependence of the GaAs band gap. The pressure coefficients of the intersubband transitions are both composition and well-width dependent. Several reasons that could influence the numerical value of the pressure coefficients have been considered and discussed by taking into account the effects of strain and alloying as well as quantum confinement. We suggest that the built-in strain-induced coupling of the confined-electron subbands with the hole valence band and hydrostatic-pressure-induced change of defect behavior in the vicinity of the interface of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As and GaAs such as dislocations should be taken into consideration to account for the behavior of pressure dependence of intersubband transitions in this multiple-quantum-well system.