We report a combined experimental/modeling study of optical emission from the A 2 Δ, B 2 Σ − , and C 2 Σ + states of the CH radical in microwave (MW) activated CH 4 /H 2 gas mixtures operating under a range of conditions relevant to the chemical vapor deposition of diamond. The experiment involves spatially and wavelength resolved imaging of the CH(C → X), CH(B → X), and CH(A → X) emissions at different total pressures, MW powers, C/H ratios in the source gas, and substrate diameters. The results are interpreted by extending an existing 2D (r, z) plasma model to include not just electron impact excitation but also chemiluminescent (CL) bimolecular reactions as sources of the observed CH emissions. Three possible CL reactions (of H atoms with CH 2 (a 1 A 1 ) and CH 2 (X 3 B 1 ) radicals and of C( 1 D) atoms with H 2 ) are identified as plausible sources of electronically excited CH radicals (particularly of the lowest energy CH(A) state radicals). Each or all of these could contribute to the observed emissions and, collectively, are deduced to be the major source of the CH(A) emissions observed at the high temperatures (T gas ∼ 3000 K) and pressures (75 ≤ p ≤ 275 Torr) explored in the present study. We suggest that such CL contributions are likely to be commonplace in such high pressure, high temperature plasma environments and highlight some of the risks associated with using relative emission intensities as an indicator of the electron characteristics in such plasmas.

Piezoelectric properties of wurtzite AlN and GaN/AlN are investigated using scanning force microscopy (SFM). The magnitude of the effective longitudinal piezoelectric constant d33 of AlN and GaN/AlN thin films are measured and reported, and the d33 coefficients of these films are verified using an interferometric technique. Simultaneous imaging of the topography, and of the phase and magnitude of the piezoelectric strain is performed. Using a GaN film with patterned polarities, we demonstrate that polarity can be inferred from the phase image of the piezoelectric strain. We report d33=3±1 pm/V for AlN/SiC and 2 1 pm/V for GaN/AlN/SiC. Films grown by organo-metallic vapor phase epitaxy (OMVPE) on SiC, sputtered AlN films and films grown by molecular beam epitaxy (MBE) are characterized and compared.

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