Why diamond is the best semiconductor?
Ask any electronics engineer “what is the ultimate semiconductor material?”, and the majority will say “diamond”. It is clarify why the comparative table of properties by exponents of gallium nitride and silicon carbide always omit the diamond column from their presentations!
|
Property (relative to silicon) |
Si |
GaAs |
GaN |
SiC |
Diamond |
|
Thermal conductivity |
1 |
0.3 |
0.9 |
3.1 |
13.5 |
|
Thermal expansion coefficient |
1 |
1.6 |
2.2 |
1.6 |
0.03 |
|
Dielectric constant |
1 |
1.06 |
0.9 |
0.9 |
0.5 |
|
Electron mobility |
1 |
5.67 |
0.83 |
0.67 |
3.0 |
|
Hole mobility |
1 |
0.67 |
0.42 |
0.08 |
6.3 |
|
Saturated carrier velocity |
1 |
1 |
2.2 |
2 |
>2.5 |
Unlike other wide band gap materials, diamond has the potential to be able to clearly differentiate itself against existing silicon on cost per switched watt and performance. The simple fact is that diamond is ideal material to meet the needs of the energy systems switching of today and tomorrow, where the need exists to precisely control the flow of electricity from watts to megawatts. Beyond power electronics, diamond has a wide potential of electronics applications that exploit other facets of diamonds superior capabilities.
Despite its obvious intrinsic advantages, diamond has struggled in the past to make any significant progress as a semiconductor material. The reason for this because of is one widely held perception: lack of large diameter single crystal wafers. Wafer sizes up to 25 mm is available in the single-crystal form, while income-generating production requests the wafer size at list 75 mm in diameter.
How to make large area single crystal substrates?
The route to larger area substrates is through a process known as “mosaic”. A “tiles” of carefully cut and polished single crystal diamonds are assembled so that they form a tightly packed array with a flat surface. The seed diamonds are usually sourced from commercially available high pressure high temperature (HTHP) or chemical vapor deposition (CVD) grown substrates. The mosaic is heated to between 700ºC and 1000ºC in a mixture methane gas and hydrogen at around 1/10 of an atmosphere. A microwave energy source is use to ionize the gas into a plasma that liberates carbon from the gas that bind with the seed substrate to form new diamond. As the new diamond grows the film knits together at the tile boundaries to create a homogenous single crystal diamond substrate with few boundary defects. The thicker the growth layer the fewer the number of tiling defects. The grown diamond film is wet chemistry separated from appropriate pre-treated seed substrates. The preparation of the seed surface is repeated prior to starting the new growth. By cycling of pre-treatment and growth stages, multiple free standing substrates with the same crystal orientation can be produced. These substrates can then be either used as starter tiles to create larger substrates. Stepping up to larger areas is just a matter of using bigger tiles and/or more tiles in single growing cycle. This is not theory; it’s reality with several growers now able to produce large area substrates. The problem is the substrates market price. By rough estimation the price will be higher then 60k$ for 75 mm wafer. It makes the production senseless.
We know how to produce the large diameter diamond wafers by reasonable price.
For more information please, contact us.