Ga 3dexcitons at surfaces and interfaces

Soft-x-ray–emission spectroscopy has been used to investigate Ga 3d core excitons associated with the surface and bulk of GaAs(110) during growth of overlayers of Sn, Bi, Ge, Fe, Ti, and Al. Remarkably, the Ga 3d exciton emission persists despite the growth of 50-Å-thick overlayers. These results demonstrate a novel pathway to exciton formation beneath the overlayer, where they are associated with bulk ${\mathit{L}}_6$ and ${\mathit{X}}_6$ band-edge states. They also show a broadening of the 20-eV Ga 3d emission feature that depends on the interface growth mode.