BROADENING OF INTERBAND RESONANCES IN THIN ALAS BARRIERS EMBEDDED IN GAAS

AlAs barriers embedded in GaAs were studied by spectroscopic ellipsome try and resonant Raman scattering. Heterostructures with AlAs barrier widths ranging from 2 to 30 nm were grown by molecular-beam epitaxy at growth temperatures between 410 and 660 degrees C. For layer widths b elow 10 nm the E(1) and E(1) + Delta(1) critical point resonance in th e dielectric function of the AlAs was found to broaden and to be smear ed out completely for a width of 2 nm. Resonant Raman scattering by th e AlAs LO phonon reveals for layer widths less than or equal to 10 nm a considerable broadening of also the E(0) interband transition in the AlAs. The magnitude of the critical point broadening and redistributi on of oscillator strength, however, was found to be independent of the growth temperature and thus of the cation intermixing observed by Ram an spectroscopy for growth temperatures greater than or equal to 600 d egrees C. Therefore, the observed critical point broadening is not cau sed by the formation of graded composition (AlGa)As barriers. Instead, the broadening of interband resonances is attributed to a spread of t he carrier wave functions into the surrounding GaAs, which are not con fined within the AIAs barrier for neither the E(0) nor the E(1) and E( 1) + Delta(1) interband transitions. (C) 1996 American Institute of Ph ysics.