Magnetophotoluminescence and change in photoluminescence (PL) intensities, due to far-infrared irradiation at the cyclotron resonance (CR) magnetic fields, in modulation-doped ${\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ single heterostructures are measured. The changes in PL intensities due to CR absorption strongly depend on the Landau-level filling factor $\left(\nu \right)$ and CR energy; i.e., the Landau-level separation. When $\nu <2\mathrm{}$ and CR energy is more than intersubband energy separation, luminescence from the ground subband is almost quenched and that from the second subband is greatly enhanced by CR absorption.

• Received 29 June 1998

DOI:https://doi.org/10.1103/PhysRevB.58.15385