Impurity-free interdiffusion in GaAs/Al _0.54Ga _0.46As multiple quantum wells capped with PECVD SiO _x: Effect of nitrous oxide flow

Impurity-free vacancy interdiffusion of GaAs/Al _0.54Ga _0.46As quantum wells (QWs) was achieved using SiO _x capping followed by rapid thermal annealing at 950 °C. The SiO _x films were plasma deposited using N ₂O/SiH ₄ flow at 300 °C and 20 W rf power. The stoichiometry of capping layers were altered by varying the flowrate of N ₂O. In the samples studied, the above process allows continuously variable energy shifts as high as approximately 150 meV while still maintaining clearly resolved excitonic behavior. The degree of intermixing is not controlled by x only but, also, by the density of the SiO _x layers. Our results, therefore, suggest that, in addition to the solid solubility of Ga in SiO _x, intermixing in SiO _x-capped MQW heterostructures depends on the mobility of Ga atoms in the oxide caps.