Chemical epitaxy of semiconductor thin films
- PDF / 652,353 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 5 Downloads / 237 Views
Introduction Chemical bath deposition (CBD) of thin semiconducting films is the aqueous analogue of chemical vapor deposition (CVD) in the gas phase. Deposition of epitaxial semiconductor films via the inexpensive, easily scalable, near room temperature CBD method is an alternative approach for advanced electronic, optoelectronic, and energy conversion applications. However, growth from aqueous solution is considered to be more complicated than that in the vapor phase due to the generally lower purity of the reactants and the complex interactions of the reactants with water (or solvent) molecules. Freund and Suresh defined epitaxial growth as “continuation of the registry or alignment of crystallographic atom positions in the single crystal substrate into the single crystal film. More precisely, an interface between film and substrate crystals is epitaxial if atoms of the substrate material at the interface occupy natural lattice positions of the film material and vice versa. The two materials need not be of the same crystal class for this to be the case, but they commonly are so.”1 Smith provided a more general definition: “Epitaxy means that the crystallographic order of the film is being significantly influenced by that of the substrate as a result of some degree of matching between the two along the interface.”2 Venables suggested that the definition of epitaxy has become more general over the years: “The term epitaxy has come to mean the growth of one layer in a particular crystallographic orientation relationship to the underlying, or substrate, layer.”3 In Anna Osherov, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, [email protected] Yuval Golan, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, [email protected]
790
MRS BULLETIN • VOLUME 35 • OCTOBER 2010 • www.mrs.org/bulletin
this review article, we use the term chemical epitaxy in the latter sense in order to indicate the presence of a well-defined orientation relationship between the CBD single crystal film and substrate, in which the crystallographic axes of the film are aligned with, but not necessarily parallel to, those of the substrate. CBD can normally proceed by one of two principal mechanisms: (1) The cluster mechanism, which can involve deposition either via cluster formation of the desired compound in solution followed by migration to the substrate, or deposition of clusters of intermediate composition on the substrate followed by chemical conversion to the desired compound to form a nanocrystalline film. (2) The ion-by-ion mechanism, in which deposition occurs directly onto a substrate with (ideally) no precipitation in the deposition solution.4 It has been previously established that laser light scattering can be qualitatively used for determining the active deposition mechanism in CBD.5,6 Although epitaxy usually requires a certain degree of lattice matching between semiconductor film and substrate, chemical interactions between the constituents of the deposition solution and the substrate are often critical. Indeed, due to the
Data Loading...
