Thickness dependence of disorder in pseudomorphic modulation-doped Al_xGa_1-xAS/In_yGa_1-yAs/GaAs heterostructures

摘要

The dependence of disorder on In_yGa_1-yAs thickness in pseudomorphic strained-layer Al_xGa_1-x As/In_yGa_1-yAs/GaAs heterostructures is studied by means of photoluminescence (PL) and Raman scattering. PL and Raman data indicate that, for both y = 0.10 and 0.15, the In_yGa_1-yAs layers (with thickness not greater than 20 nm) are purely pseudomorphically strained. For In_yGa_1-yAs wells narrower than about 15 nm, the broad PL emission, small correlation length derived from Raman measurements of the longitudinal optical (LO) phonons, the asymmetry of the LO phonon peak and the presence of a disorder-activated longitudinal acoustic (DALA) phonon signal in the Raman scattering data are all indicative of disordered InGaAs. For well widths of 20 nm, however, the narrow PL emission, the details of the LO phonon data and the absence of an observable DALA signal are all indicative of much less disorder than in the thinner quantum wells.