| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS+EM+MS+TF-MoM |
| Session: | Spectroscopic Ellipsometry I |
| Presenter: | S.G. Choi, National Renewable Energy Laboratory |
| Authors: | S.G. Choi, National Renewable Energy Laboratory C. Martinez-Tomas, Universitat de Valencia, Spain V. Munoz Sanjose, Universitat de Valencia, Spain D.H. Levi, National Renewable Energy Laboratory |
| Correspondent: | Click to Email |
III-VI compounds generally crystallize in layered-structures characterized by strong covalent interactions within the layers but weak Van der Waals binding between the layers. This unique structural characteristic has made III-VI compounds attractive for their potential applications in nonlinear optics. Among these compounds, in particular, InSe has been considered as a promising candidate for thin film photovoltaic (PV) material owing to its energy bandgap, optical and transport properties. Recently, high-quality epitaxial InSe thin films have been grown on GaSe substrates, and PV device structures containing n-InSe and p-GaSe have been successfully fabricated [1].
In order to design and optimize a high-performance PV device structure, knowledge of optical properties of constituent materials over a wide spectral range is required. However, large discrepancies were found in the properties of GaSe and InSe available in the literature, which have been measured mostly by reflectance methods with the Kramers-Kronig transformation employed to obtain the dielectric functions. Here, we present ellipsometrically determined pseudodielectric function <ε>=<ε1>+i<ε2> spectra from 0.73 to 6.45 eV of bulk GaSe (ε-phase) and InSe (γ-phase) single-crystals grown by a vertical Bridgman method. The surfaces with minimum overlayers were obtained by peeling off the top few layers from the sample surface and ellipsometric measurements were immediately followed under flowing N2 environment, which yields good approximations to the intrinsic dielectric responses. The measured spectra exhibited a number of interband-transition critical-point structures, and their energy values were obtained precisely from numerically calculated second-energy-derivatives of <ε> assuming the parabolic-band critical-point model.
Data obtained in this work can be used to model PV device structures utilizing GaSe and InSe, and the critical-point energies determined will be useful for theoreticians to perform fine band structure calculations of III-VI compounds.
The work done at Universitat de València was supported in part by the Spanish Project MAT2007-06841. This abstract is subject to U.S. government rights.
[1] J.F. Sánchez-Royo, J. Appl. Phys. 90, 2818 (2001).