X-ray photoelectron spectroscopy is used to measure the valence-band offset in situ for GaAs/AlAs(100) heterojunctions grown by molecular-beam epitaxy. $\mathrm{Ga} 3d$ and $\mathrm{Al} 2p$ core-level to valence-band-edge binding-energy differences are measured in GaAs(100) and AlAs(100) samples, respectively, and the $\mathrm{Al} 2p$ to $\mathrm{Ga} 3d$ core-level binding-energy difference is measured in GaAs-AlAs(100) and AlAs-GaAs(100) heterojunctions. (Note that GaAs-AlAs indicates a heterojunction with GaAs grown on top of AlAs; GaAs/AlAs refers collectively to both growth sequences.) Measurements of the $\mathrm{Al} 2p$ to $\mathrm{Ga} 3d$ core-level energy separations indicate that the band offset for GaAs/AlAs(100) is commutative; the value we obtain is $\Delta E_v=0.45\mathrm{}\pm 0.07$ eV. Our observation of commutativity is believed to be a consequence of the high quality of our GaAs/AlAs(100) heterojunctions, and of the inherent commutativity of the band offset in this heterojunction system.

• Received 16 May 1988

DOI:https://doi.org/10.1103/PhysRevB.38.12764