Characterization of monolayer-level composition and optical gap profiles in amorphous silicon-carbon alloy bandgap-modulated structures
Conference
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OSTI ID:20085527
Over the past few years the authors have applied real time spectroscopic ellipsometry (RTSE) to characterize the structural, compositional, and optical gap profiles in continuously-graded amorphous silicon-carbon alloy films (a-Si{sub 1{minus}x}C{sub x}:H). Most recently, they have extended the RTSE methods to their monolayer sensitivity and resolution limits. In this study, continuous triangular variations in the carbon content x (0.02 {le} x {le} 0.24) within {approximately}25 to 130 {angstrom} thick graded layers were introduced at the i/p interfaces of the n-i-p solar cell structures using continuous variations in the flow ratio z = [CH{sub 4}]/{l_brace}[SiH{sub 4}]+[CH{sub 4}]{r_brace} during rf plasma-enhanced chemical vapor deposition (PECVD). A virtual interface approximation has been applied to interpret the RTSE data collected during the growth of the graded interface layers. This analysis yields C-content depth-profiles with monolayer-level resolution and a compositional uncertainty of {+-}0.004. Even compositional gradients in which x changes by 0.2 within a few monolayers' thickness are readily characterized. Lastly, a continuous increase in open circuit voltage with increasing graded interface layer thickness, saturating at {Delta}V{sub oc} = 0.1 V after 100 {angstrom}, is observed in the n-i-p solar cells with graded layers. These results demonstrate the importance of the RTSE analysis in assessing bandgap engineered device designs.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (US)
- OSTI ID:
- 20085527
- Country of Publication:
- United States
- Language:
- English
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