Thickness dependence of disorder in pseudomorphic modulation-doped AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures

The dependence of disorder on InyGa1-yAs thickness in pseudomorphic straine d-layer Al-x Ga1-xAs/InyGa1-yAs/GaAs heterostructures is studied by means o f photoluminescence (PL) and Raman scattering. PL and Raman data indicate t hat, for both y = 0.10 and 0.15, the InyGa1-yAs layers (with thickness not greater than 20 nm) are purely pseudomorphically strained. For InyGa1-yAs w ells narrower than about 15 nm, the broad PL emission, small correlation le ngth derived from Raman measurements of the longitudinal optical (LO) phono ns, the asymmetry of the LO phonon peak and the presence of a disorder-acti vated longitudinal acoustic (DALA) phonon signal in the Raman scattering da ta are all indicative of disordered InGaAs. For well widths of 20 nm, howev er, the narrow PL emission, the details of the LO phonon data and the absen ce of an observable DALA signal are all indicative of much less disorder th an in the thinner quantum wells.