Real-Time Spectroscopic Ellipsometry of Sputtered CdTe Thin Films: Effect of Ar Pressure on Structural Evolution and Photovoltaic Performance

Abstract

In this study, 1 μm thick polycrystalline CdTe films were deposited by magnetron sputtering using a variable argon pressure, 2.5 ≤ pAr ≤ 50 mTorr, and a fixed substrate temperature, Ts = 230°C. Real time spectroscopic ellipsometry (RTSE) was performed during deposition in order to analyze the nucleation and coalescence, as well as the evolution of the surface roughness thickness ds with bulk layer thickness db and the depth profile in the void volume fraction fv. A linear correlation was found between the final ds value measured by RTSE at the end of deposition and the root-mean-square (rms) surface roughness measured by atomic force microscopy (AFM) ex situ after deposition. A monotonic decrease in RTSE-determined roughness thickness is observed with decreasing Ar pressure from 18 to 2.5 mTorr. The lowest pressure also leads to the greatest bulk layer structural uniformity; in this case, fv increases to 0.04 with increasing CdTe thickness to 1 μm. The photovoltaic performance of CdTe films prepared with the lowest pressure of pAr = 2.5 mTorr is compared with that of previously optimized CdTe solar cells with pAr = 10 mTorr.

This is a preview of subscription content, access via your institution.

References

  1. [1]

    R. Messier, A.P. Giri, and R.A. Roy, J. Vac. Sci. Technol. A 2, 500 (1984).

    Article  Google Scholar 

  2. [2]

    V. Plotnikov, A. Vasko, A.D. Compaan, X. Liu, K. Wieland, R. Zeller, J. Li, and R.W. Collins, Mat. Res. Soc. Symp. Proc. (MRS, Warrendale PA, 2009), Vol. 1165, Art. No. 1165-M09-01.

  3. [3]

    J. Li, J.A. Stoke, N.J. Podraza, D. Sainju, A. Parikh, X. Cao, H. Khatri, N. Barreau, S. Marsillac, X. Deng, and R.W. Collins, in: Photovoltaic Cell and Module Technologies, edited by B. von Roedern and A.E. Delahoy, (SPIE, Bellingham, 2007), Vol. 6651, Art. No. 6651-07.

  4. [4]

    D. E. Aspnes, Am. J. Phys. 50, 704 (1981).

    Article  Google Scholar 

  5. [5]

    J. Li, J. Chen, N.J. Podraza, and R.W. Collins, Conf. Record of the IEEE 4th World Conf. on Photovoltaic Energy Conversion 2006, (IEEE, Piscataway NJ, 2006) p. 392.

  6. [6]

    J. Lee, P.I. Rovira, I. An, and R.W. Collins, Rev. Sci. Instrum. 69, 1800 (1998).

    CAS  Article  Google Scholar 

  7. [7]

    B. Johs, J.A. Woollam, C.M. Herzinger, J.N. Hilfiker, R. Synowicki, and C. Bungay, Proc. Soc. Photo-Opt. Instrum. Eng., Crit. Rev. 72, 29 (1999).

    Google Scholar 

  8. [8]

    X. Wu, P. Sheldon, Y. Mahathongdy, R. Ribelin, A. Mason, H.R. Moutinho, and T.J. Coutts, AIP Conf. Proc. 462, 37 (1999).

    CAS  Article  Google Scholar 

  9. [9]

    B. E. McCandless and J. R. Sites, in: Handbook of Photovoltaic Science and Engineering, edited by A. Luque and S. Hegedus, (John Wiley and Sons, 2003) p. 632.

  10. [10]

    G.A. Niklasson, C.G. Granqvist, and O. Hunderi, Appl. Opt. 20, 26 (1981).

    CAS  Article  Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to Michelle N. Sestak.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Sestak, M.N., Li, J., Paudel, N.R. et al. Real-Time Spectroscopic Ellipsometry of Sputtered CdTe Thin Films: Effect of Ar Pressure on Structural Evolution and Photovoltaic Performance. MRS Online Proceedings Library 1165, 902 (2009). https://doi.org/10.1557/PROC-1165-M09-02

Download citation