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MORGaN topic
Diamond substrates
Diamond has been known for centuries for its excellent optical and mechanical
properties. Another property of diamond, which is less well known to the man in
the street, is the tremendous thermal conductivity, reaching 2,000 Wm-1°C-1
for mono-crystal, which is the highest of any solid material. It is followed by
silicon carbide and metals like copper, which show a thermal conductivity four to
five
times lower.
As such, diamond is potentially the ultimate substrate for many high temperature or extreme power applications. Gallium nitride (GaN) alloys were studied intensively thirty years ago but breakthroughs were demonstrated only about fifteen years ago in optical applications (e.g. blue LED, blue laser, lightning etc.) and more recently have demonstrated impressive power handlings from DC to microwave operation with breakdown field reaching over 5MVcm-1.
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| Three forms of diamond: single crystal substrates, optical grade polycrystalline and mechanical grade polycrystalline. |
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MORGaN aims to develop hybrids combining the excellent thermal behaviour of polycrystalline diamond with the electrical efficiency of GaN compounds. GaN has a moderate thermal conductivity (c. 190Wm-1°C-1); slightly better than Si, but three times lower than SiC and ten times lower than mono-crystalline diamond. The GaN thermal conductivity represents a bottleneck to power dissipation. The pure electrical power handling potential of GaN-based devices is at least thirty times higher than Si-based equivalents, while the thermal resistance of the best GaN devices grown on SiC is only improved by a factor two, due to the contribution of the GaN on the total resistance.
MORGaN will target the full potential of GaN without being limited by the thermal conductivity of SiC.
