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 lm 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 Ssurface ¼ (2.8 6 0.3) 105 cm s1 ) and at the heteroepitaxial interface (interface recombination velocity Sinterface ¼ (4.8 6 0.5) 105 cm s1 ). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe. VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4896673]

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