STUDY OF ALMBE GROWTH-CONDITIONS FOR THE PREPARATION OF COMPOSITIONALLY GRADED ALGAAS/GAAS STRUCTURES

We have studied ALMBE growth conditions which give high quality structures with continuous or abrupt grading of Ga1-xAlxAs composition. Four 50 angstrom thick GaAs/Alx(i)Ga1-x(i)As (x(i)=0.3, 0.5, 0.7 and 1.0) quantum wells (QWs) and a direct-gap (GaAs)9/(AlAs)2 superlattice were stacked on the same sample by changing the supply times of cations instead of modifying molecular beam fluxes (x resolution approximately 1%). Linewidths of photoluminescence (PL) transitions, as narrow as 2.0-2.5 meV, suggest that interfaces grown at low temperature are pseudosmooth. We have also grown parabolically graded QWs that exhibit remarkably sharp PL linewidths and show exciton transitions, observed by optical absorption measurements, at energies very close to the expected values.