Suppression of interdiffusion in InGaAs/GaAs quantum dots using dielectric layer of titanium dioxide

Abstract

In this work, titanium dioxide (TiO₂)film was deposited onto the In₀.₅Ga₀.₅As/GaAs quantum-dot structure by electron-beam evaporation to investigate its effect on interdiffusion. A large redshifted and broadened spectrum from the dot emission was observed compared with that from the uncapped (but annealed) reference sample, indicating the suppression of thermal interdiffusion due to TiO₂deposition. The structure was also capped with a silicon dioxide (SiO₂) single layer or SiO₂/TiO₂ bilayer with the thickness of SiO2 varied from ∼6 to ∼145 nm. In the former case, an increased amount of impurity-free vacancy disordering (IFVD) was introduced with the increase of SiO₂ thickness due to the enhanced Ga outdiffusion into the film. With TiO₂deposited on top, IFVD and thermal interdiffusion were suppressed to different extents with the variation of SiO₂ thickness. To explain the suppression of interdiffusion, thermal stress introduced by the large thermal expansion coefficient of TiO₂ (when compared with GaAs) as well as the metallurgical reactions between the TiO₂ and GaAs were proposed as possible mechanisms. Show more