The effect of controlled impurity incorporation on interfacial roughness in GaAs/Al xGa 1− xAs superlattice structures grown by metalorganic vapor phase epitaxy

Abstract

Oxygen impurities are known to degrade the bulk and heterointerfacial quality of Al x Ga 1− x As/GaAs layers grown by metalorganic vapor phase epitaxy (MOVPE). We have intentionally added oxygen at the interfaces of Al 0.3Ga 0.7As/GaAs superlattice layers to examine its effect on interfacial and surface roughness in these structures. Small angle X-ray diffraction and atomic force microscopy (AFM) were used to quantify and compare both small scale interfacial roughness and large scale surface roughness. Interfacial oxygen incorporation was found to increase with increasing substrate misorientation angle off (100) toward the (110) and this was reflected in increased interfacial roughness. Large scale surface structures with spacings of ∼2.0 μm were observed using AFM for growth on nominally (100) substrates. The existence of these features is also indicated in X-ray correlated roughness measurements. A mechanism of preferential oxygen incorporation at surface step edges is proposed to explain the evolution of roughness in the superlattice layers.