A technique for the measurement of surface diffusion coefficient and activation energy of Ge adatom on Si(001)

Abstract

A method for determining the surface diffusion coefficient and the activation energy of Ge adatoms on Si(001) has been developed. Ge self-assembled quantum dots (SAQDs) grown on a relaxed SiGe buffer layer preferentially nucleate over a network of buried 60° dislocations. The surface sites over the buried dislocations act as sinks of Ge adatoms. When the average dislocation spacing becomes larger than the surface diffusion length of Ge adatoms, denuded zones free of Ge SAQDs appear on both sides of buried dislocations and separating the preferentially nucleated SAQDs from the randomly nucleated ones. The denuded zone width and the inter-dot spacing of randomly nucleated SAQDs are completely dependent on the surface diffusion coefficient. By varying the substrate temperature during the growth, the activation energy for the surface diffusion can be determined from the equilibrium inter-dot spacing of the randomly nucleated Ge SAQDs. Moreover, the pre-exponential term in the diffusion constant can be determined by using Fick’s first law and the observation that the total incident flux of Ge adatoms impinging on the denuded zones equals the average rate of volume increase of SAQDs over dislocations. The diffusion coefficient of Ge adatoms on Si (001) is found to be Ds≅2.53×10−7 exp(−0.676±0.03 eV/kT) cm2/s in the temperature range from 650 to 725 °C.