The conduction-band offset in $\mathrm{GaAs}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells is determined with a new light scattering method. A value of $\frac{\Delta E_c}{\Delta E_g}=Q_e=0.69\mathrm{}$ is found for $x\simeq 0.06$. The conduction-band discontinuity $\Delta E_c$ is obtained from electronic light scattering in a photoexcited sample. The total gap discontinuity $\Delta E_g$ is deduced from resonance Raman scattering by ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ phonons in the same sample. The light scattering method is unique because $\Delta E_c$ can be determined regardless of the valence-band structure or exciton binding energies. It also allows a direct measurement of $\Delta E_g$, so that an exact knowledge of the alloy composition in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ is no longer needed.

• Received 27 February 1986

DOI:https://doi.org/10.1103/PhysRevB.33.8863