Lattice mismatch and atomic structure studies on In xGa 1− xAs/In yAl 1− yAs coupled double-step quantum wells

Abstract

Lattice mismatch and atomic structure studies of In x Ga 1− x As/In y Al 1− y As coupled double-step quantum wells have been performed by transmission electron microscopy (TEM) and electron-diffraction pattern measurements. The high-resolution TEM image of the In x Ga 1− x As/In y Al 1− y As coupled double-step quantum well showed that two sets of a 60-Å In 0.65Ga 0.35As deep quantum well and a 60-Å In 0.53Ga 0.47As shallow step quantum wells bounded by two thick In 0.52Al 0.48As barriers are separated by a 38-Å In 0.52Al 0.48As embedded potential barrier. The selective-area electron-diffraction pattern obtained from TEM measurements on the In x Ga 1− x As/In y Al 1− y As double-step quantum well showed that In x Ga 1− x As active layers were grown pseudomorphologically on the InP buffer layer. The value of the lattice mismatch between the In 0.53Ga 0.47As and the In 0.65Ga 0.35As layers obtained from the high-resolution TEM measurements is 1.6%. A possible crystal structure for the In x Ga 1− x As/In y Al 1− y As coupled double-step quantum well is presented based on the TEM results. These results can help improve understanding of the structural properties for the applications of strained In x Ga 1− x As/In y Al 1− y As coupled double-step quantum wells in new kind of the optoelectronic devices.