Explanation of red spectral shifts at CdTe grain boundaries

• Published in: Applied physics letters Vol. 103; no. 23
• Main Authors: Moseley, J., Al-Jassim, M. M., Moutinho, H. R., Guthrey, H. L., Metzger, W. K., Ahrenkiel, R. K.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 02-12-2013
• Subjects: Applied physics; Cadmium tellurides; Cathodoluminescence; Grain boundaries; Photovoltaic cells; Red shift; Solar cells; Sublimation; Thin films
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4838015

We use cathodoluminescence spectrum imaging to investigate the nanoscale properties of CdTe thin-films for solar cells deposited by close-spaced sublimation. Luminescence emission is detected (bands) at ∼1.32 eV and ∼1.50 eV, which are consistent with Z- and Y-bands. For the grains in the as-deposited films, there is a significant redshift in the transition energies near the grain boundaries. The high grain boundary recombination velocity and the donor-acceptor pair (DAP) mechanism of the Z-band transition account for the contrast between grain boundaries and the grain interior. By applying DAP theory, we estimate the concentration of the shallow donor species participating in the Z-band transition to be ∼1017 cm−3.