A series of experiments was carried out to compare the structural and electronic properties of intrinsic nanocrystalline silicon (nc-Si:H) thin films deposited via continuous wave (cw) and pulsed (p)-PECVD at 150°C substrate temperature. Working at this temperature allows for the easy transfer of film recipes from glass to plastic substrates in the future. During the p-PECVD process the pulsing frequency was varied from 0.2 to 50 kHz at 50% duty cycle. Approximately 15% drop in the deposition rate was observed for the samples fabricated in p-PECVD compared to cw-PECVD. The optimum crystallinity and photo (σph) and dark conductivity (σD) were observed at 5 kHz pulsing frequency, with ~10% rise in crystallinity and about twofold rise in the σph and σD compared to cw-PECVD. However, for both the cw and p-PECVD nc-Si:H films, the observed σph and σD were one to two orders and three orders of magnitude higher respectively than those reported in literature. The average activation energy (EA) of 0.16 ∓ 0.01 eV for nc-Si:H films deposited using p-PECVD confirmed the presence of impurities, which led to the observation of the unusually high conductivity values. It was considered that the films were contaminated by the impurity atoms after they were exposed to air. Following the thin film characterization procedure, the optimized nc-Si:H film recipes, from cw and p-PECVD, were used to fabricate the absorber layer of thin film solar cells. The cells were then characterized for J-V and External Quantum Efficiency (EQE) parameters. The cell active layer fabricated from p-PECVD demonstrated higher power conversion efficiency (η) and a maximum EQE of 1.7 ∓ 0.06 % and 54.3% respectively, compared to 1.00 ∓ 0.04 % and 48.6% respectively for cw-PECVD. However, the observed η and EQE of both the cells were lower than a reported nc-Si:H cell fabricated via p-PECVD with similar absorber layer thickness. This was due to the poor Short-circuit Current Density (Jsc), Open-circuit Voltage (Voc), and Fill Factor (FF) of the cw and p-PECVD cells respectively, compared to the reported cell. The low Jsc resulted from the poor photocarrier collection at longer and shorter wavelengths and high series resistance (Rseries). On the other hand, the low Voc stemmed from the low shunt resistance (Rsh). It was inferred that the decrease in the Rsh occurred due to the inadequate electrical isolation of the individual cells and the contact between the n – layer and the front TCO contact at the edge of the p-i-n deposition area. Additionally, the net effect of the high Rseries and the low Rsh led to a decrease in the FF of the cells.

A series of experiments was carried out to compare the structural and electronic properties of intrinsic nanocrystalline silicon (nc-Si:H) thin films deposited via continuous wave (cw) and pulsed (p)-PECVD at 150°C substrate temperature. Working at this temperature allows for the easy transfer of film recipes from glass to plastic substrates in the future. During the p-PECVD process the pulsing frequency was varied from 0.2 to 50 kHz at 50% duty cycle. Approximately 15% drop in the deposition rate was observed for the samples fabricated in p-PECVD compared to cw-PECVD. The optimum crystallinity and photo (σph) and dark conductivity (σD) were observed at 5 kHz pulsing frequency, with ~10% rise in crystallinity and about twofold rise in the σph and σD compared to cw-PECVD. However, for both the cw and p-PECVD nc-Si:H films, the observed σph and σD were one to two orders and three orders of magnitude higher respectively than those reported in literature. The average activation energy (EA) of 0.16 ∓ 0.01 eV for nc-Si:H films deposited using p-PECVD confirmed the presence of impurities, which led to the observation of the unusually high conductivity values. It was considered that the films were contaminated by the impurity atoms after they were exposed to air. Following the thin film characterization procedure, the optimized nc-Si:H film recipes, from cw and p-PECVD, were used to fabricate the absorber layer of thin film solar cells. The cells were then characterized for J-V and External Quantum Efficiency (EQE) parameters. The cell active layer fabricated from p-PECVD demonstrated higher power conversion efficiency (η) and a maximum EQE of 1.7 ∓ 0.06 % and 54.3% respectively, compared to 1.00 ∓ 0.04 % and 48.6% respectively for cw-PECVD. However, the observed η and EQE of both the cells were lower than a reported nc-Si:H cell fabricated via p-PECVD with similar absorber layer thickness. This was due to the poor Short-circuit Current Density (Jsc), Open-circuit Voltage (Voc), and Fill Factor (FF) of the cw and p-PECVD cells respectively, compared to the reported cell. The low Jsc resulted from the poor photocarrier collection at longer and shorter wavelengths and high series resistance (Rseries). On the other hand, the low Voc stemmed from the low shunt resistance (Rsh). It was inferred that the decrease in the Rsh occurred due to the inadequate electrical isolation of the individual cells and the contact between the n – layer and the front TCO contact at the edge of the p-i-n deposition area. Additionally, the net effect of the high Rseries and the low Rsh led to a decrease in the FF of the cells.

Nanocrystalline silicon (nc-Si:H) is a promising material for Thin-Film Transistors (TFTs) offering potentially higher mobilities and improved stability over hydrogenated amorphous silicon (a-Si:H). The slow growth rate of nc-Si:H can be overcome by using pulsed Plasma-Enhanced Chemical Vapour Deposition (PECVD). Pulsed PECVD also reduces powder particle formation in the plasma and provides added degrees of freedom for process optimization. Unlike high frequency PECVD, pulsed PECVD can be scaled to deposit films over large areas with no reduction in performance. For this thesis, silicon thin films were deposited by the pulsed PECVD technique at a temperature of 150 ??C and TFTs were made using this material. Radio Frequency (RF) power and silane (SiH₄) flow rate were varied in order to study the effect of different levels of crystallinity on the film. Raman spectroscopy, Atomic Force Microscope (AFM), X-Ray Diffraction (XRD), electrical conductivity, Hall mobility, optical band gap, and stability under light-soaking were measured using films of two different thicknesses, 50 nm and 300 nm. From the Raman data we see that the 50 nm films deposited with high hydrogen dilution are mostly amorphous, indicating the presence of a thick incubation layer. The 300nm samples deposited with hydrogen dilution, on the other hand, showed very high crystallinity and conductivity, except for 300-2 which was surprisingly, mostly amorphous. AFM and XRD measurements were also performed to confirm the Raman data and get an estimate for the crystallite grain size in the 300 nm samples. The conductivity was measured for all films, and the Hall mobility and carrier concentration was measured for one of the 300 nm films. The thin samples which are mostly amorphous show low conductivity whereas the thick high crystallinity films show high conductivity, and n-type behaviour possibly due to oxygen doping. The optical gap was also measured using Ultra Violet (UV) light and results indicate the possible presence of small crystallites in the 50 nm films. The conductivity's stability under light-soaking was measured to observe the material's susceptibility to degradation, and the 300 nm with high crystallinity were much more stable than the a-Si:H films. All the results of these measurements varied depending on the film and these results are discussed. Bottom-gate TFTs were fabricated using a pulsed PECVD channel layer and an amorphous silicon nitride (a-SiN:H) gate dielectric. The extracted parameters of one of the best TFTs are <i>&mu;_sat</i> &le; 0. 38 cm² V^-1 s^-1, <i>V_t,sat</i> &ge; 7. 3 V, <i>I_on/off</i> > 10⁶, and <i>S</i> < 1 V/decade. These parameters were extracted semi-automatically from the basic Field-Effect Transistor (FET) model using a computer program. Extraction using a more complicated model yielded similar results for mobility and threshold voltage but also gave a large power parameter <i>&alpha;</i> of 2. 31 and conduction band tail slope of 30 meV. The TFT performance and material properties are presented and discussed. On this first attempt at fabricating TFTs using a nc-Si:H channel layer deposited by pulsed PECVD, results were obtained which are consistent with results for low temperature a-Si:H TFTs and previous pulsed PECVD TFTs. The channel layer was mostly amorphous and non-crystalline, possibly due to the amorphous substrate or insufficient hydrogen dilution in the plasma. The 300 nm films showed, however, that high crystallinity material deposited directly on glass can easily be obtained, and this material showed less degradation under light-soaking than the purely amorphous counterpart. Pulsed PECVD is a promising technique for the growth of nc-Si:H and with further materials development and process optimization for TFTs, it may prove to be useful for the growth of high-quality nc-Si:H TFT channel layers.

Nanocrystalline silicon (nc-Si:H) is a promising material for Thin-Film Transistors (TFTs) offering potentially higher mobilities and improved stability over hydrogenated amorphous silicon (a-Si:H). The slow growth rate of nc-Si:H can be overcome by using pulsed Plasma-Enhanced Chemical Vapour Deposition (PECVD). Pulsed PECVD also reduces powder particle formation in the plasma and provides added degrees of freedom for process optimization. Unlike high frequency PECVD, pulsed PECVD can be scaled to deposit films over large areas with no reduction in performance. For this thesis, silicon thin films were deposited by the pulsed PECVD technique at a temperature of 150 °C and TFTs were made using this material. Radio Frequency (RF) power and silane (SiH₄) flow rate were varied in order to study the effect of different levels of crystallinity on the film. Raman spectroscopy, Atomic Force Microscope (AFM), X-Ray Diffraction (XRD), electrical conductivity, Hall mobility, optical band gap, and stability under light-soaking were measured using films of two different thicknesses, 50 nm and 300 nm. From the Raman data we see that the 50 nm films deposited with high hydrogen dilution are mostly amorphous, indicating the presence of a thick incubation layer. The 300nm samples deposited with hydrogen dilution, on the other hand, showed very high crystallinity and conductivity, except for 300-2 which was surprisingly, mostly amorphous. AFM and XRD measurements were also performed to confirm the Raman data and get an estimate for the crystallite grain size in the 300 nm samples. The conductivity was measured for all films, and the Hall mobility and carrier concentration was measured for one of the 300 nm films. The thin samples which are mostly amorphous show low conductivity whereas the thick high crystallinity films show high conductivity, and n-type behaviour possibly due to oxygen doping. The optical gap was also measured using Ultra Violet (UV) light and results indicate the possible presence of small crystallites in the 50 nm films. The conductivity's stability under light-soaking was measured to observe the material's susceptibility to degradation, and the 300 nm with high crystallinity were much more stable than the a-Si:H films. All the results of these measurements varied depending on the film and these results are discussed. Bottom-gate TFTs were fabricated using a pulsed PECVD channel layer and an amorphous silicon nitride (a-SiN:H) gate dielectric. The extracted parameters of one of the best TFTs are <i>&mu;_sat</i> &le; 0. 38 cm² V^-1 s^-1, <i>V_t,sat</i> &ge; 7. 3 V, <i>I_on/off</i> > 10⁶, and <i>S</i> < 1 V/decade. These parameters were extracted semi-automatically from the basic Field-Effect Transistor (FET) model using a computer program. Extraction using a more complicated model yielded similar results for mobility and threshold voltage but also gave a large power parameter <i>&alpha;</i> of 2. 31 and conduction band tail slope of 30 meV. The TFT performance and material properties are presented and discussed. On this first attempt at fabricating TFTs using a nc-Si:H channel layer deposited by pulsed PECVD, results were obtained which are consistent with results for low temperature a-Si:H TFTs and previous pulsed PECVD TFTs. The channel layer was mostly amorphous and non-crystalline, possibly due to the amorphous substrate or insufficient hydrogen dilution in the plasma. The 300 nm films showed, however, that high crystallinity material deposited directly on glass can easily be obtained, and this material showed less degradation under light-soaking than the purely amorphous counterpart. Pulsed PECVD is a promising technique for the growth of nc-Si:H and with further materials development and process optimization for TFTs, it may prove to be useful for the growth of high-quality nc-Si:H TFT channel layers.