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Production Of Hydrogenated Nanocrystalline Silicon Based Thinfilm TransistorAliyeva, Tamila 01 July 2010 (has links) (PDF)
The instability under bias voltage stress and low mobility of hydrogenated amorphous
silicon (a-Si:H) thin film transistor (TFT), produced by plasma enhanced chemical vapor deposition
(PECVD) technique, are the main problems impeding the implementation of active
matrix arrays for light emitting diode display panels and their peripheral circuitry. Replacing
a-Si:H by hydrogenated nanocrystalline silicon film (nc-Si:H) seems a solution due to its
higher mobility and better stability. Therefore nc-Si:H TFT was produced and investigated in
this thesis.
All TFT layers (doped nc-Si:H, intrinsic nc-Si:H and insulator films) were produced separately,
characterized by optical (UV-visible and FTIR spectroscopies, XRD) and electrical
(current-voltage, I-V) methods, and optimized for TFT application. Afterwards the non
self-aligned bottom-gate TFT structure was fabricated by the photolithographic method using
2-mask set.
The n+ nc-Si:H films, used for TFT drain/source ohmic contacts, were produced at high
H2 dilution and at several RF power densities (PRF). The change of their lateral resistivity
(rho) was measured by reducing the film thickness via reactive ion etching. The rho values rise
below a critical film thickness, indicating the presence of the disordered and less conductive
incubation layer. The optimum PRF for the lowest incubation layer was determined.
Among the deposition parameters only increased NH3/SiH4 flow rate ratio improved the
insulating properties of the amorphous silicon nitride (a-SiNx:H) films, chosen as the TFT
gate dielectric. The electrical characteristics of two TFTs with a-SiNx:H having low leakage
current, fabricated at different NH3/SiH4 ratios (~19 and ~28) were compared and discussed.
The properties (such as crystallinity, large area uniformity, etc.) of the nc-Si:H film as
TFT channel layer, were found to depend on PRF. For the films deposited at the center of
the PECVD electrode the change from an amorphous dominant structure to a nanocrystalline
phase took place with increasing PRF, whereas those at the edge had always nanocrystalline
nature, independent of PRF. The two different TFTs produced at the center of the electrode
with a-Si:H and nc-Si:H grown at low and high PRF, respectively, were compared through
their I-V characteristics and electrical stability under the gate bias voltage stress.
Finally, nc-Si:H TFT structure, produced and optimized in this work, was analyzed through
gate-insulator-drain/source capacitor by capacitance-voltage (C-V) measurements within
106-10-2 Hz frequency (F) range. The inversion regime was detected at low F without any
external charge injection. Besides, ac hopping conductivity in the nc-Si:H bulk was extracted
from the fitting results of the C-F curves.
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Dynamic variation of hydrogen dilution during hot-wire chemical vapour deposition of silicon thin filmsTowfie, Nazley January 2013 (has links)
It has been debated that among all the renewable energy alternatives, only solar energy offers sufficient resources to meet energy demands. Silicon thin film solar cells are at the frontier of commercial solar technology. Hot wire chemical vapour deposition (HWCVD) is the technique of choice for silicon thin film deposition due to the absence of ion bombardment and its independence toward geometry or electromagnetic properties of the substrate, as seen by plasma enhanced chemical vapour deposition (PECVD). With the implementation of nanostructures in a
multi-band gap tandem solar cell, considerable improvement has been achieved over the single junction solar cells. Defect assisted tunnelling processes at the junctions between individual solar cells in a tandem structure solar cell largely affect the efficiency of these solar cells. In this contribution, the investigation toward the improvement of silicon thin films for tandem solar cell application is initiated. This study reports on the effects of hydrogen dilution and deposition time on six silicon thin films deposited at six specific deposition regimes. The thin film properties are investigated via X-Ray diffraction analysis, Raman spectroscopy, Fourier transform infra-red spectroscopy, elastic recoil detection analysis, scanning and transmission electron microscopy and UV-visible spectroscopy. This investigation revealed the dominating etching effect of atomic hydrogen with
the increase in hydrogen dilution and a bonded hydrogen content (CH) exceeding 10 at.% for each of the six thin films. The optically determined void volume fraction and static refractive index remain constant, for each thin film, with the change in CH. A new deposition procedure, utilising the deposition conditions of the previously investigated thin films, is performed by HWCVD to deposit two silicon thin films. This deposition procedure involved either increasing (protocol 1) or decreasing (protocol 2) hydrogen dilution during deposition. Structural and optical variation with depth was observed for the dynamically deposited silicon thin films, with nano-voids existing across the entire cross section and bond angle variations which are indicative of good structural order. The optical absorption curves differ for the two silicon thin films whereas the optical density remains constant for both. / >Magister Scientiae - MSc
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Dynamic variation of hydrogen dilution during hot-wire chemical vapour deposition of silicon thin filmsTowfie, Nazley January 2013 (has links)
>Magister Scientiae - MSc / This study reports on the effects of hydrogen dilution and deposition time on six silicon thin films deposited at six specific deposition regimes. The thin film properties are investigated via X-Ray diffraction analysis, raman spectroscopy, fourier transform infra-red spectroscopy, elastic recoil detection analysis, scanning and transmission electron microscopy and UV-visible spectroscopy. This investigation revealed the dominating etching effect of atomic hydrogen with
the increase in hydrogen dilution and a bonded hydrogen content (CH) exceeding 10 at.% for each of the six thin films. The optically determined void volume fraction and static refractive index remain constant, for each thin film, with the change in CH
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Macroscopic and Microscopic surface features of Hydrogenated silicon thin filmsPepenene, Refuoe Donald January 2018 (has links)
Magister Scientiae - MSc (Physics) / An increasing energy demand and growing environmental concerns regarding the use of fossil
fuels in South Africa has led to the challenge to explore cheap, alternative sources of energy.
The generation of electricity from Photovoltaic (PV) devices such as solar cells is currently
seen as a viable alternative source of clean energy. As such, crystalline, amorphous and
nanocrystalline silicon thin films are expected to play increasingly important roles as
economically viable materials for PV development. Despite the growing interest shown in these
materials, challenges such as the partial understanding of standardized measurement protocols,
and the relationship between the structure and optoelectronic properties still need to be
overcome.
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