Si-rich Silicon Carbide Thin-Film Solar Cells
Date Issued
2010
Date
2010
Author(s)
Lo, Tzu-Chieh
Abstract
The non-stoichiometric silicon carbide (Si1-xCx) film deposited by plasma enhanced chemical vapor deposition (PECVD) system. At the same gaseous flow ratio, chamber pressure and RF power, changing substrate temperature 250 and 450℃ affect the different deposition condition. According to the SIMS analysis, we observe that the substrate plays an important role on the oxygen-exclusive synthesis and stabilized crystallization of SiC material. In s250 sample annealing 850℃ for 10 min, the oxygen content invaded entire film under 250℃ lower substrate temperature deposition condition and the intensity of O rose to 9.7×105 counts. In addition, silicon atoms content decreased to only 0.3×105 counts and carbon atoms content almost vanished in the film. On the contrary, in s450 sample, the oxidation depth is about 20 nm and the O element component intensity from 9.6×105 counts return to 4.0×105 counts. The same tendency illustrate in XPS measurement, the phase transformation of Si-C to relatively strong SiO2 and graphite/diamond related Si(2p3) and C(1s) XPS signals can be obtained from the oxidized SiC with numerous Si-O and C-C bonds formed during annealing. The solution to solve incorporated oxygen deposition and better stacking sequence of crystalline structure is increasing deposition temperature as shown in SIMS analysis. Moreover, we not only purge chamber by Ar gas during vacuum but also make use of Ar gas substitute for N2 as furnace annealing gas. However, the self-assembled Si starts to appear with increase annealing temperature up to 850℃. The volume density of Si-QDs, with an average diameter of 3±1 nm formatted in annealed Si-rich S1-xCx, is controlled at 4.35×1018 cm-3 after 1050℃ annealing temperature by HR-TEM image analysis. The I-V characteristic of SiC thin film solar cells: ITO/n-type SiC/p-type Si/Al, the open current voltage (Voc) increase from 72.5 to 205.8 mV, and the short current density (Jsc) enhance from 0.93 to 3.01 mA/cm2 with rising PH3 doping concentration from 0.47% to 5%. With 5% PH3 doping concentration, the solar cell conversion efficiency of the n-SiC based sample is 0.16%.
Subjects
PECVD
Si-rich Si1-xCx
silicon nanocrystal
SiC thin film solar cell
Type
thesis
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