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Observation and implications of the Franza??Keldysh effect in ultrathin GaAs solar cells
摘要： Voltage-dependencies were observed in the external quantum efficiency (EQE) spectra of ultrathin GaAs solar cells. The subbandgap tail was shown to increase going from forward to reverse bias, while at energies above the bandgap, voltage-dependent oscillations in the EQE were measured. Using optical simulations, it is irrefutably shown that the voltage-dependencies are caused by the Franz-Keldysh effect, that is, an electric field-dependent absorption coefficient near the bandgap. The dependency on voltage of the subbandgap tail is demonstrated to be strongest in thin-film cells with a textured rear mirror, since the absorptivity below the bandgap is enhanced by light trapping. The voltage-dependent subbandgap tail has important implications for the use of the reciprocity relation between photovoltaic quantum efficiency and electroluminescence. It is shown that the radiative limit for the open-circuit voltage of thin-film cells integrated with light management schemes can be underestimated by more than 25 mV. Consequently, these cells may be assumed to be closer to the radiative limit than they really are.
关键词： Urbach tail,Franz-Keldysh effect,reciprocity,textured solar cells,ultrathin gaas
更新于2025-09-23 15:21:01
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Analysis of Optical Integration between Si3N4 Waveguide and a Ge-Based Optical Modulator Using a Lateral Amorphous GeSi Taper at the Telecommunication Wavelength of 1.55 μm
摘要： We report on the theoretical investigation of using an amorphous Ge0.83Si0.17 lateral taper to enable a low-loss small-footprint optical coupling between a Si3N4 waveguide and a low-voltage Ge-based Franz–Keldysh optical modulator on a bulk Si substrate using 3D Finite-Difference Time-Domain (3D-FDTD) simulation at the optical wavelength of 1550 nm. Despite a large refractive index and optical mode size mismatch between Si3N4 and the Ge-based modulator, the coupling structure rendered a good coupling performance within fabrication tolerance of advanced complementary metal-oxide semiconductor (CMOS) processes. For integrated optical modulator performance, the Si3N4-waveguide-integrated Ge-based on Si optical modulators could simultaneously provide workable values of extinction ratio (ER) and insertion loss (IL) for optical interconnect applications with a compact footprint.
关键词： Franz–Keldysh effect,germanium,optical interconnect,silicon nitride
更新于2025-09-11 14:15:04