EFFECT OF SUBSTRATE MISCUT ON THE STRUCTURAL-PROPERTIES OF INGAAS LINEAR GRADED BUFFER LAYERS GROWN BY MOLECULAR-BEAM EPITAXY ON GAAS

We investigated the effect of substrate misorientation on the structural properties of an InGaAs linearly compositionally graded buffer layer and an AlGaAs/InGaAs superlattice grown by molecular-beam epitaxy on both on-axis and 2° miscut (001) GaAs substrates. Triple axis x-ray diffraction and reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. A tilt of 0.17° between the buffer layer and substrate was observed from (004) reciprocal space maps of the heterostructure grown on an off-axis substrate, while none was observed for the heterostructure grown on the on-axis substrate. The layer tilt axis for the miscut substrate, which coincided with a 〈110〉 direction, was 32° from the miscut axis. (224) glancing exit reciprocal space maps showed the majority of the buffer layer to be relaxed, with the top portion corresponding to a strained denuded zone free of misfit segments. Intersubband measurements showed no relation between device performance and the 2° miscut substrate, even though the two samples exhibited different superlattice peak widths.