Silicon has long been the foundation of semiconductor technology, in part because it is more abundant and less expensive than compound semiconductors such as the Group III - V semiconductor GaAs. However, silicon has limited applications as an optoelectronic device owing to its reduced carrier mobility and its indirect band gap. This difficulty may be circumvented by alloying other Group IV elements, such as carbon, germanium, or tin, to form strained epitaxial thin films on silicon substrates. There has been much attention focused on the alloying of tin with germanium or silicon. It has even been predicted that alloys of Si1-xSnx and Ge1-xSnx on silicon may possess tunable, direct bandgaps. Difficulties exist, however, owing to a large crystal lattice mismatch between tin, germanium and silicon. Tin alloy films can be stabilized by growing the films on germanium buffer layers on silicon substrates, or by depositing on substrates that more closely lattice match the film, such as germanium or indium phosphide. A second obstacle is the low equilibrium solid solubility of tin in germanium (approximately 1%) and in silicon (less than 0.1%). This can be avoided by using non-equilibrium growth techniques such as molecular beam epitaxy and chemical vapor deposition.To date, chemical vapor deposition is the only practical method used by industry to develop devices based on thin films. Recently, researchers at ASU discovered the first chemical method for tin incorporation in silicon-based semiconductor materials.Now, this same researchers group has devised a new chemical method for the synthesis and use of a new tin compound to deposit films of tin alloyed with carbon, germanium, or silicon or to dope films made from Group IV or III - V elements. The compound is the only stable substance possessing the necessary vapor pressure at room temperature, making it an ideal tin source in CVD applications. The decomposition pathway of the compound produces stable byproducts, which do not interfere with the decomposition process nut do prevent impurity incorporation in the film. The invention has been used in an UHV CVD chamber to grow alloyed films of Ge1-xSnx and Si1-x-yCxSny. Rutherford Backscattering Spectroscopy (RBS) has been used to characterize these films.
|Original language||English (US)|
|State||Published - Sep 27 2000|