Charge-carrier transport and recombination in heteroepitaxial CdTe

We analyze charge-carrier dynamics using time-resolved spectroscopy and varying epitaxial CdTe thickness in undoped heteroepitaxial CdTe/ZnTe/Si. By employing one-photon and nonlinear two-photon excitation, we assess surface, interface, and bulk recombination. Two-photon excitation with a focused laser beam enables characterization of recombination velocity at the buried epilayer/substrate interface, 17.5 mu m from the sample surface. Measurements with a focused two-photon excitation beam also indicate a fast diffusion component, from which we estimate an electron mobility of 650 cm(2) (Vs)(-1) and diffusion coefficient D of 17 cm(2) s(-1). We find limiting recombination at the epitaxial film surface (surface recombination velocity S-surface - (2.8 +/- 0.3) x 10(5) cm s(-1)) and at the heteroepitaxial interface (interface recombination velocity S-interface - (4.8 +/- 0.5) x 10(5) cm s(-1)). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe. (C) 2014 AIP Publishing LLC.