MULTIPLE SUBBAND POPULATION IN DELTA-DOPED ALASSB INGAAS HETEROSTRUCTURES/

We have measured the Shubnikov-de Haas (SdH) effect in delta-doped AlA s0.56Sb0.44/In0.53Ga0.47As heterostructures and observed a population of the second subband. Using the persistent photoconductivity effect w e increased the electron density from 26.73 to 28.20x10(11) cm(-2) in the first subband and 6.61 to 7.20X10(11) cm(-2) in the second. The on set of the second subband population occurs when the first subband is filled to a density of 11.56x10(11) cm(-2). From the nonparabolic band approximation we calculated the effective masses in both subbands bef ore illumination. The effective mass for the second subband was evalua ted using the temperature dependence of the SdH amplitude. Its value a grees well with the values obtained from the k . p approximation and i nfrared cyclotron resonance measurements. (C) 1997 American Institute of Physics.