The X-ray emission yield by the Al-2p core-exciton excitation in GaAs/AlAs/
GaAs heterostructures is studied theoretically: especially the angular corr
elation between absorbed and emitted X-rays are discussed. It becomes clear
that the angular dependence of the X-ray emission yield is drastically cha
nged according to the excitation character whether 2p --> s or 2p --> d tra
nsitions.