NEAR-BAND-EDGE RESONANT STATES OF ALAS MONOLAYERS EMBEDDED IN BULK GAAS - THE ROLE OF D SYMMETRIES

We present empirical tight-binding and ab initio pseudopotential calcu lations of the electronic states in GaAs/(AlAs)(n)/GaAs (100) structur es with n=1 and 2. For n=1, we find that a resonant state occurs in th e valence-band at the GaAs edge. The existence of this state, which ca nnot be accounted for in an effective-mass picture, is due to the nonl ocal angular-momentum-dependent potential describing the single-atom s ubstitution GaAs:Al-Ga. The p component of this potential is repulsive for the GaAs electrons, consistently with the local effective-mass de scription. However, its d component is attractive and is responsible f or the occurrence of the resonant state at the GaAs valence-band edge. For n=2 the resonant state occurs at lower energy than in the n=1 cas e (the tight-binding model predicts the resonance 26 meV below the GaA s valence-band edge) and its coupling with the continuum is stronger. The variation of the energy position of this resonance with the thickn ess of (AlAs)(n) layers could be responsible for the large differences recently observed in the luminescence spectra of n=1 and 2 structures . [S0163-1829(98)00807-8].