|
There are several extreme properties) of diamond which make it a desireable material for technological applications. Its hardness, which is related to its large elastic moduli, is well known. Less widely recognized are its high thermal conductivity and its low thermal expansion coefficient, which suggest its use in high temperature applications. Its large bandgap of 5.5 eV suggests uses in optical electronics in the VUV region, but the indirect nature of the gap has contributed to the lack of active investigation of diamond as an optical component. More important in this regard is the problem of fabrication of diamond components: the stable form of carbon is graphite, with the cubic (and hexagonal) forms of carbon being metastable. This metastability is primarily a limitation only in the fabrication process; once tetrahedrally-bonded carbon is formed it is exceedingly "stable", even up to high temperatures.
The recent progress in the area of vapor deposition of diamond has been encouraging. An overview of the various methods which have been used has been given by Moustakas et al. 2 Moreover, fabrication of operating p-n diodes on the related material BN by Mishima et al.,3 constructed by growing n-type BN on p-type seed crystals, suggests that the construction of diamond-based electronic components may not be far away. For applications involving the epitaxial growth of diamond on nearly lattice-matched materials, it is crucial to understand the effects of the various uniaxial strains which may occur. A question of special importance is: are there physically realizable strains which will lead to an indirect-to-direct gap inversion, making it more amenable to application in electronic/optical devices. In this paper we provide the initial results of our investigation of these questions.
Several studies of the shifts in band energies due to infinitesimal strains ("deformation potentials") have appeared. Most of these 4-8 have dealt only with homogeneous strains, although uniaxial strains have received some attention. 9, 10 Nielsen ll has carried out extensive studies of the stress-strain relationship in diamond under uniaxial deformations, but reported very little (recounted below) on the effects on the band structure.
|
