Non-equilibrium thermodynamics and the vapor phase preparation of diamond for electronic applications

Bulk diamond is unstable relative to bulk graphite except at high pressure and temperature. In spite of this, well crystallized diamond has been grown using numerous CVD methods, many of which have in common the production of atomic hydrogen and hydrocarbon radicals in regimes where solid carbon is expected to be a stable product. Several fundamentally different points of view have emerged in the effort to explain why well crystallized diamond, and not graphite or vitreous carbon, is observed in these experiments. One of the earliest argues that graphite is “etched” by atomic hydrogen at a rate higher than diamond and hence diamond is kinetically stable with respect to graphite. If diamond formation is kinetically controlled the deposition mechanism is critical and much debate has centered on the mechanism and species involved. Alternatively it can be argued that at the growth interface, diamond surfaces are stabilized by termination with hydrogen. If this is correct, and bulk reorganization ignored, then it is shown that a global understanding of the parameters important to the growth of diamond can be obtained without detailed kinetic analyses. Thus it is argued that single crystal diamond films of arbitrarily high purity and perfection are theoretically possible by CVD in spite of the bulk instability of diamond. It is also suggested that general principles exist which might be applied to the growth of other well crystallized metastable phases-notably cubic boron nitride.