Gallium Arsenide vs. Silicon

In the beginning of the project, our group investigated whether it was more advantageous to manufacture integrated chips made from Gallium Arsenide or from Silicon. The benefits of using Gallium Arsenide (GaAs) over Silicon (Si) are:

• Both discrete components and integrated circuits made in GaAs are faster than those made of silicon because its low-field electron mobility is larger than that of silicon, and GaAs has a lower saturation field than silicon.
• GaAs has an energy gap that is four orders of magnitude larger than Si. This allows GaAs to be made semi-insulating (with a bulk resistivity on the order of 10^9 ohms). Devices made in semi-insulating GaAs substrates have reduced parasitic capacitance which leads to further improvement in speed over silicon.
• GaAs has the ability to emit light which is useful for making lasers, light-emitting diodes, and microwave emitters used in cellular phones. (It is a direct band gap material)

However, we discovered that even with these advantages, gallium arsenide has not been able to out-compete silicon due to several disadvantages:

• is more rare and difficult to obtain than silicon. Silicon is readily available at any beach, and is second in abundance on Earth only to oxygen.
• Arsenic is very toxic, so much so that its minimal use as a dopant in silicon chips is creating problems with handling and disposal of GaAs circuits.
•  arsenide lacks the silicon's ability to use its oxide form as an ideal insulator which can be used as a mask to protect the silicon. This increases the complexity of its manufacturing process, resulting in a higher manufacturing costs.
• 
  arsenide has poor thermal conductivity compared to silicon (the thermal conductivity of silicon is 2.75 times larger than that of gallium arsenide). As a result, the packing densities achievable with GaAs circuits are less than Si circuits. Also, the amount of RpowerS that a GaAs integrated circuit can handle is severely limited. Often times, GaAs slices have to be mechanically or chemically thinned prior to mounting on a header, a process with a high chance of wafer breakage. This is inefficient.

As a result, silicon remained the dominant material for semiconductors while the market for gallium arsenide circuits remained very small. Currently, silicon comprises 95% of the semiconductor industry whereas arsenide comprises only 5% of the semiconductor market. This has led to our choice of creating a space manufacturing facility that focusses on silicon computer chip production. However, even though our facilities will mainly manufacture silicon chips, once the station is established, it can be adapted to produce other types of chips, such as arsenide integrated circuits. These circuits would be expensive, however, in part because the conductor is gold as opposed to aluminum. arsenide is used in microwave devices (in other words: high speed communications). arsenide is a very efficient electricity-light converter, making it a good component of solar panels. The most efficient solar panels we have today are made from silicon and ø arsenide.

Being in space presents us with another opportunity: there, we can develop a facility that uses both  arsenide and silicon since in orbit there is no cross contamination. Gold is toxic to silicon, and arsenide and silicon are dopants for each other. Without gravity, cross contamination does not occur.

We are hearing that the new material of the future may not be arsenide, but rather silicon germanium. It is reputedly easier to work with and has several electrical advantages, without being severely toxic to us.