Silicon-tin or SiSn, is in general a term used for an alloy of the form Si_(1-x)Sn_x. The molecular ratio of

tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

can vary based on the fabrication methods or doping conditions. In general, SiSn is known to be intrinsically semiconducting, and even small amounts of Sn doping in silicon can also be used to create strain in the silicon lattice and alter the charge transport properties.

Theoretical studies

Several theoretical works have shown SiSn to be semiconducting. These mainly include

DFT The Department for Transport (DfT) is a ministerial department of the Government of the United Kingdom. It is responsible for the English transport network and a limited number of transport matters in Scotland, Wales, and Northern Ireland t ...

-based studies. The band structures obtained using these works show a change in band gap of silicon with the inclusion of tin into the silicon lattice. Thus, like SiGe, SiSn has a variable band gap that can be controlled using Sn concentration as a variable. In 2015, Hussain et al. experimentally verified the tuning of band gap associated with the diffusion of tin using homogeneous, abrupt p-n junction diodes.

Production

SiSn can be obtained experimentally using several approaches. For small quantity of Sn in silicon, the

Czochralski process The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, plati ...

is well known. Diffusion of tin into silicon has also been tried extensively in the past. Sn has the same valency and

electronegativity Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...

as silicon and can be found in the

diamond cubic In crystallography, the diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, in ...

crystal structure (α-Sn). Thus, silicon and tin meet three out of the four

Hume-Rothery rules Hume-Rothery rules, named after William Hume-Rothery, are a set of basic rules that describe the conditions under which an element could dissolve in a metal, forming a solid solution. There are two sets of rules; one refers to substitutional sol ...

for solid state solubility. The one criterion that is not met is that of difference in atomic size. The tin atom is substantially larger than the silicon atom (31.8%). This reduces the solid state solubility of tin in silicon.

Electrical performance

The first

MOSFET upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale. In electronics, the metal–oxide–semiconductor field- ...

(metal–oxide–semiconductor field-effect transistor) using SiSn as a channel material was shown in 2013. This study proved that SiSn can be used as semiconductor for MOSFET fabrication, and that there may be certain applications where the use of SiSn instead of silicon may be more advantageous. In particular, the off current of SiSn transistors is much lower than that of silicon transistors. Thus, logic circuits based on SiSn MOSFETs consume lower static power compared to silicon-based circuits. This is advantageous in battery operated devices (LSTP devices), where the standby power has to be reduced for longer battery life.

Thermal conductivity

Si-Sn alloys have the lowest conductivity (3 W/mK) of all the bulk alloys among Si-Ge, Ge-Sn, and Si-Ge-Sn; less than half that of Si-Ge which has been extensively studied, attributed to the larger difference in mass between the two constituents. In addition, thin films offer an additional reduction in

thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...

, reaching around 1 W/mK in 20-nm-thick Si-Sn, Ge-Sn, and ternary Si-Ge-Sn films, which is near the conductivity of amorphous SiO₂. Group-IV alloys containing Sn have the potential for high-efficiency

thermoelectric The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when ...

energy conversion.

References

{{Reflist Silicon alloys Tin alloys

Theoretical studies

Production

Electrical performance

Thermal conductivity

See also

References