The effect of partial hydrogen dilution on the mostly helium diluted silane plasma in controlling the nanocrystallization process in the Si : H network was studied systematically. The parametric conditions were chosen in such a way as to produce the basic matrix as a mixed phase heterogeneous material in the neighbourhood of the amorphous to nanocrystalline transition zone, but dominated by the amorphous component, which could easily trigger nanocrystallization on favourable parametric changes. The relative influence of He and H2 was closely monitored, by virtue of their individual presence in the plasma in different proportions, in the nanocrystallization process that might occur within the Si : H network. Controlled hydrogenation to such a heterogeneous structure, during growth, has been identified as the favoured route for attaining spontaneous nanocrystallization in the network. The beneficial aspects of He-dilution in enhancing the growth rate and initiating nanocrystallization within the heterogeneous structure was simply added to the habitual effect of H2-dilution in the promotion of crystallization in the Si : H network. Using partial H2-dilution in trivial amounts to the mostly He-diluted SiH4 plasma and combining their individual influences, highly conducting intrinsic nc-Si : H films were produced at high growth rate from (SiH4 + He + H2)-plasma in rf PECVD and that introduces enormous technological promise for efficient utilization of the material in the fabrication of devices.
The evolution of nc-Si network and the control of its growth within quantum dot structures have been systematically studied by He/H2 plasma assistance in SiH4. Using the beneficial aspects of He* and He+ in the purely helium-diluted silane plasma and optimizing the process parameters, nanocrystalline silicon films are produced at high growth rates. The nc-Si:H network of increasing electrical conductivity and improved crystallinity are obtained with simultaneously increasing deposition rates, which deserve extensive technological impact. Starting with a mixed phase heterogeneous matrix in the neighborhood of amorphous-to-crystalline transition zone, the effect of H2 in the reconstruction of the network, triggering nanocrystallization, was studied using (SiH4+He+H2)-plasma. A radical change in the materials properties has been accomplished by the inclusion of a small amount of H2 as the component diluent. Sharp rise in the overall crystallinity, well aligned crystallographic lattice distribution, gross removal of porosity and sharp elevation of electrical conductivity by several orders of magnitude are the consequences which are accompanied by a relatively insignificant lowering in the growth rate because of required H2-dilution in trivial amounts. Partial hydrogenation to the mostly He diluted SiH4 plasma has been identified as the favored route for attaining spontaneous nanocrystallization in the Si-network and its confinement of structures within quantum dot dimensions.
The effect of direct current (dc) substrate bias on the promotion of nanocrystallization in Si network has been studied, specifically within He-diluted SiH 4 plasma in radio frequency (RF)-plasma-enhanced chemical vapor deposition. In view of organizing nanocrystallinity, controlled transmission of energy to the growing surface is needed and that is obtainable from metastable helium (He*) bombardment and, in particular, ionic helium (He + ) bombardment under negative substrate bias. The structural morphology has been adequately regulated to a homogeneous network restraining from an exclusive columnar structure that is coherent to low-temperature growth. Notable improvements in the film quality in terms of enhanced crystallinity with low hydrogen content as well as reduced incubation volume, bulk void, and surface roughness have been demonstrated, even at low substrate temperature and low RF power. Use of appropriate dc substrate-bias has been identified as a supplementary parameter efficiently organizing the growth, making it more device-friendly.
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