Resonance enhanced inelastic light scattering from a quasi-two-dimensional electron gas confined at the interface of abruptly doped $\mathrm{GaAs}/n-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterojunctions has been measured. The samples were fabricated using molecular-beam epitaxy with a high-contrast doping technique. The results show strong evidence for intersubband excitations in a two-dimensional electron system.

• Received 21 December 1978

DOI:https://doi.org/10.1103/PhysRevLett.42.1308