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-μm 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 cm² (Vs)^-1 and diffusion coefficient D of 17 cm² s^-1. We find limiting recombination at the epitaxial film surface (surface recombination velocity S_surface = (2.8 ± 0.3) × 10⁵cm s^-1) and at the heteroepitaxial interface (interface recombination velocity S_interface = (4.8 ± 0.5) × 10⁵cm 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.