Diploma Thesis - Erich Schmid Institute

Basic Physical Properties
During cooling, starting from the melting point at 1410°C, silicon crystallises in the
diamond structure without showing allotropic transformation in the solid state. The
cooling process is associated with the thermal contraction of the silicon material that
has a thermal expansion coefficient of 2,616 10 -6 K -1 at room temperature [13].
6.2. Monocrystalline GaN on monocrystalline sapphire
6.2.1. GaN
Unfortunately, bulk crystals of nitrides cannot be obtained by conventional methods of
liquid phase epitaxy, because of extremely high melting temperatures and very high
decomposition pressures at the melting point.
Several production techniques are available for growing thin gallium nitride (GaN)
films. These methods can be divided in two groups, one where chemical reactions play
an important role and the other one where only physical process are responsible for
the layer formation. For example a representative of the first group would be
metalorganic vapour deposition (MOCVD) technique or reactive sputtering and for
instance a production method belonging to the second group would be molecular
beam epitaxy (MBE).
Figure 6.3: Diamond structure
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