CARBON ACCEPTOR LUMINESCENCE IN TYPE-I GAAS ALAS ULTRATHIN-LAYER SUPERLATTICES/

The luminescence associated with residual carbon acceptors in type-I ( direct-gap) ultrathin-layer superlattices (UTLS) with well and barrier widths of 22.7 < L(z) < 25.2 angstrom and 11.5 < L(b) < 14.0 angstrom , respectively, is composed of two lines reflecting the on-center and on-edge state of the impurities. In these narrow wells the on-center a cceptor binding energy increases to 60 meV in agreement with theoretic al calculations for GaAs single quantum wells using a valence band off set of 500 meV. While the binding energy of the on-center state does n ot vary significantly within the studied L(z) and L(b) range, the on-e dge state shows a strong dependence on the very narrow barrier width. This increase of the acceptor binding energy makes the energy position of the impurity-related luminescence in UTLS very sensitive to the ac tual barrier height. Investigation of the impurity-related luminescenc e thus provides a versatile tool to determine the band offset ratio at the heterojunction.