Influence of Limited Efficiency and Competition of Vacancy Sinks/Sources on the Diffusion-Controlled Intermediate Phase Growth

Kinetics and structural evolution of the intermediate phase layer formation during reactive diffusion is revisited. Main new input is an account of limited efficiency of vacancy sinks/sources at the moving interfaces and in the bulk, leading to nonequilibrium vacancy concentration gradients. Competition of the two types of vacancy sinks/sources is studied – K-sinks (providing Kirkendall lattice shift) and F-sinks (Frenkel-Kirkendall voids formation). Reactive diffusion with limited vacancy sources/sinks power in isothermal regime as well as in adiabatic SHS-regime is considered.

Nonequilibrium Vacancies in Nanosystems

The influence of nonequilibrium vacancy distribution, generated by a difference of intrinsic fluxes of components under limited efficiency of vacancy sinks/sources, on various diffusion processes, is analyzed. Interdiffusion, reactive diffusion, reactive phase growth under electric current, spinodal decomposition, collapse of compound nanoshells, ripening are considered.

Self-Diffusion as A Limiting Factor of a-SiGe Crystallization

ABSTRACTHighly doped (∼1018 to 1021cm−3) polycrystalline Si1-xGex films, crystallized from amorphous (a) state at relative low temperatures, are prospective materials in a variety of applications, such as liquid-crystal displays, solar cells and integrated thermoelectric sensors on large-area glass substrates. Since the nature of the grains in the crystallized film defines properties such as carrier mobility, the nucleation and growth process of the a-SiGe films is of fundamental interest. We have studied the crystallization of undoped and highly doped (B or Ga) amorphous SiGe films. The films were deposited by RFCVD or molecular beam on oxidized (001)Si and for TEM study on cleaved NaCl. The incubation time and grain growth rate were studied by means of in situ TEM using a heating stage. The crystallization process in undoped SiGe followed Avrami relationship. An average grain size between 0.1 and 2μm was observed. However, the highly p-doped (with B or Ga) SiGe films crystallized to a stable nanocrystalline structure (grain size <10nm). The process of the a-SiGe crystallization is explained on the basis of self-diffusion. During the first stage, the nucleation of crystals is accompanied with nonequilibrium vacancy generation at the amorphous/crystalline interface. During the second stage, the growth of crystals takes place by vacancy outdiffusion which is hindered by B and Ga interaction with vacancies.