OSCILLATORY MAGNETOABSORPTION OF MULTILAYER QUANTUM-WELL STRUCTURES

The oscillatory magnetoabsorption spectra of a periodic structure with GaAs-Al0.3Ga0.7As quantum wells (number of wells N = 20, well width L (z) almost-equal-to 130 angstrom) were recorded at T = 1.8 K in magnet ic fields H < 7.5 T by direct determination of the optical absorption in a free thin sample. The oscillatory structure was observed beginnin g in fields of 1 T, which were considerably lower than the fields H s atisfying the strong field criterion (H > 6 T). An analysis of fan di agrams demonstrated convergence, in H = 0, to positions of excited (2s ) states of a quantum-well exciton manifested by short-wavelength sing ularities near the ground (1s) states in H = 0. A preliminary analysis ignoring the binding energies of diamagnetic excitons showed that an agreement with experimental results was achieved without postulating h igher values of the effective mass at the bottom of the electron energ y band than that adopted for the bulk material.