Charge-carrier transport and recombination in heteroepitaxial CdTe

Abstract

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 Ssurface = (2.8 ± 0.3) × 105 cm s−1) and at the heteroepitaxial interface (interface recombination velocity Sinterface = (4.8 ± 0.5) × 105 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.

In-depth analysis of chloride treatments for thin-film CdTe solar cells

“…Determination of accurate carrier lifetime values for CdTe can often be problematic, however, owing to enhanced surface recombination17. This may be overcome by techniques such as two photon excitation measurements18, but here we instead employ two different single photon measurement protocols: one where excitation occurs through the glass, called ‘front surface'; and one where illumination occurs at the free CdTe back surface. Figure 4 shows both front and back surface TRPL measurements from a 10 μW 760 nm excitation (5 μm diameter spot) for (a) MgCl 2 , (b) CdCl 2 , (c) NaCl and (d) KCl-treated cells, while the average carrier lifetime values extracted are given in Fig.…”

Photoluminescence of Crystalline cDtE double heterostructures grown by MBE

“…Samples were cooled down to 4.25 K. TRPL decay curves are acquired with a Yb:KGW laser with a 300 fs pulse width, 1.1 MHz repetition rate, and 640nm wavelength for single-photon excitation. A silicon avalanche photodiode collected the PL signal for time-correlated single-photon counting [3].…”

Probing surface recombination velocities in semiconductors using two-photon microscopy

“…The procedure allows one to generate carriers at any desired depth inside the material, so that surface and bulk contributions can be disentangled in the TRPL response. We refer to the literature 4,5 for details on the operating principle and experimental setups.…”

“…We end the section using this solution to fit the experimental data obtained on heteroepitaxial CdTe/ZnTe/Si in Ref. 5. A second planar boundary in the axial direction is added in Sec.…”