Growth Chemistry of Nanocrystalline Si:H Films

Abstract

We report on the growth of nanocrystalline Si:H films using both plasma CVD and remote hot wire deposition under systematically varied growth conditions. The films were grown from mixtures of silane and hydrogen. It was found that when the films were grown under low pressure VHF plasma growth conditions , the orientation of the film changed as the pressure increased. At the lowest pressures, the films were mainly <111> oriented, but changed to <220> orientation as the pressure increased. The grain size increased as the growth temperature increased. When the films were grown using remote hot wire deposition, the orientation depended upon both hydrogen dilution and growth temperature. As the hydrogen dilution increased, the <220> grain size became smaller. Grain size as large as 36 nm was obtained by controlling the growth conditions in hot wire deposition. As the growth temperature increased, the size of <220> grains increased. Growth rates also increased with increasing temperature. The data can be explained by invoking a growth model which recognizes that the natural growth direction for Si is <220>, since the surface energy is highest for (220) plane. Random nucleation leads to <111> grains. Bonded H is believed to inhibit the growth of <220> grains.

Structural and electronic properties of nanocrystalline silicon thin film solar cells fabricated by hot wire and ECR-plasma CVD techniques

“…filament temperature was about 1800 o C. The <111> grain size increases with the hydrogen dilution whereas the <220> decreases significantly. This is because the atomic hydrogen produced due to the thermal decomposition of silane, impinging the surface of the growing film, favors the grains due to random orientation and inhibit the thermodynamically favorable <220> grains [57]. If this is the case, then the intensity of <111> grains should be enhanced as we increase the hydrogen dilution.…”

Measurement of mobility in nanocrystalline semiconductor materials using space charge limited current

“…To perform the Raman measurement a laser impinges on the sample and the photons material, so as photons are scattered a very sharp peak occurs at the wavenumber corresponding to the phonon's vibratory frequency. For crystalline silicon this wavenumber is 520cm-1 and for crystalline germanium the wavenumber is 300cm-1 [10,16,17]. If the material is amorphous it has a broad range of phonon modes due to the structural disorder.…”

“…For amorphous silicon the peak occurs at 485cm-1 and for amorphous germanium the peak occurs at 278cm-1 [10,16,17]. A Lorentzian function is used to fit the shape of the crystalline peaks and a Gaussian function is used to fit the amorphous peaks.…”