A TiO2 film was deposited onto In0.5Ga0.5As/GaAs quantum-dot structures by electron-beam evaporation in order to investigate its effect upon interdiffusion. A large red-shifted and broadened spectrum from the dot emission was observed as compared with that from an uncapped (but annealed) reference sample; thus indicating the suppression of thermal interdiffusion due to TiO2 deposition. The structure was also capped with a SiO2 single layer or a SiO2/TiO2 bilayer in which the thickness of SiO2 was varied from about 6 to 145nm. In the former case, an increased amount of impurity-free vacancy disordering was introduced with increasing SiO2 thickness, due to enhanced Ga out-diffusion into the film. With TiO2 deposited on top, impurity-free vacancy disordering 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.

Suppression of Interdiffusion in InGaAs/GaAs Quantum Dots using Dielectric Layer of Titanium Dioxide. L.Fu, P.Lever, H.H.Tan, C.Jagadish, P.Reece, M.Gal: Applied Physics Letters, 2003, 82[16], 2613-5