Measurement of nonuniform distribution of strain in InGaAs/GaAs quantum wires

Abstract

Nonuniform strain distribution in In0.2Ga0.8As/GaAs strained wires has been observed by measuring the lattice spacing from the lattice image of the cross section of a single 10 nm×400 nm wire. It was found that in the wire, the region near the wire sidewall was under a larger compressive strain in the growth direction (vertical strain) than the center of the wire. In the barrier, near the wire sidewall, GaAs was under a vertical tensile strain by the In0.2Ga0.8As wire. This observation explains experimental observation of quantum confinement in strained InGaAs/GaAs quantum wires where the possibility of nonconfining band offsets was previously hypothesized. The assumptions underlying theory which predicts the absence of quantum confinement can now be modified to include actual strain variations. The nonuniform strain distribution observed also has ramifications for stability of strained quantum wire, or buried quantum well lasers.