Optical interdonor hopping in multiple quantum wells

It is shown that the hopping transitions from neutral center-of-well donors to ionized center-of-barrier donors in multiple-quantum-well GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As heterostructures may result in an infrared-absorption maximum of the oscillator strength comparable to that for intradonor 1s-2p transitions. The weak magnetic-field dependence of the hopping transition energies makes such transitions hard to detect by variable-field magnetoabsorption techniques but they should show up in direct absorption measurements. Their detection would furnish direct information about the magnitude of electrostatic-potential fluctuations in multiple quantum wells.