Bulk and interface Al2pcore excitons in GaAs/AlAs/GaAs heterostructures

Aluminum $2p$ soft-x-ray emission and absorption spectra (XES and XAS) of a GaAs/AlAs/GaAs heterostructure semiconductor have been measured with high-energy resolution. The Al $2p$ XES shows a similar feature to that of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ alloys. Strong Al $2p$ core excitons have been observed in XAS, and attributed to the X- and L-like states in the conduction band. The XAS profile has changed depending on the incident angle of the excitation x rays. This dependence may relate to the symmetry of the exciton transitions.