SiC doubles conductivity with germanium implants

SiC doubles conductivity with germanium implantsRichard Ball
Adding germanium to wafers of silicon carbide could make the high temperature semiconductor useful in high speed electronics, according to research carried out by a professor at the University of Delaware.
James Kolodzey found that adding small amounts of germanium (Ge) to wafers of silicon carbide (SiC) doubled the conductivity of the material.
Kolodzey implanted germanium atoms into the crystal lattice of an n-type SiC wafer using an ion implanter.
X-ray diffraction of the modified material showed that adding the Ge atoms had strained the crystal lattice, so an annealing process at 1,000?C was used to reduce the strain.
X-ray diffraction and spectroscopy showed that a 0.16?m layer near the SiC surface contained around 1.2 per cent Ge. This small amount almost doubles the conductivity of the material compared with pure SiC.
This could make SiC, which doubles the useful temperature range over silicon, useable in a wider range of applications. These could include aircraft and automotive sensors and even mobile communication RF circuits.
At Newcastle University, the UK’s leading research centre for SiC, Dr Mark Johnson said:”There’s a huge potential for this material and certain sectors are pushing it hard.”
However, he said it will never replace silicon unless there’s a clear need for the high temperature operation.
Cost of production also has to come down, said Johnson. “We still need a ten times reduction in substrate costs before it’s commercially viable,” he said.
Unfortunately SiC is the third hardest substance after diamond and boron carbide, making it difficult and expensive to process. Three inch wafers are now available, (two inch commercially) but they cost around ?1,200 each. Why use SiC?
Why use SiC?With double the bandgap compared with Si, SiC needs more energy to lift valence band electrons to the conduction band. This means the breakdown voltage of devices is higher and more current can flow.
SiC has a much higher melting point than pure Si (SiC sublimes at over 1,800?C). Devices made using SiC can operate up to 600?C, when the material is glowing red-hot. Silicon, on the other hand, loses its semiconductor properties at around 325?C.
Thus SiC devices can attach directly to engines and need less cooling radiators in spacecraft.

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