Photoreflectance from GaAs and GaAs/GaAs interfaces

Quasi-Vertically-Orientated Antimony Sulfide Inorganic Thin-Film Solar Cells Achieved by Vapor Transport Deposition

The one-dimensional photovoltaic absorber material Sb₂S₃ requires crystal orientation engineering to enable efficient carrier transport. In this work, we adopted the vapor transport deposition (VTD) method to fabricate vertically aligned Sb₂S₃ on a CdS buffer layer. Our work shows that such a preferential vertical orientation arises from the sulfur deficit of the CdS surface, which creates a beneficial bonding environment between exposed Cd²⁺ dangling bonds and S atoms in the Sb₂S₃ molecules. The CdS/VTD-Sb₂S₃ interface recombination is suppressed by such properly aligned ribbons at the interface. Compared to typical [120]-oriented Sb₂S₃ films deposited on CdS by the rapid thermal evaporation (RTE) method, the VTD-Sb₂S₃ thin film is highly [211]- and [121]-oriented and the performance of the solar cell is increased considerably. Without using any hole transportation layer, a conversion efficiency of 4.73% is achieved with device structure of indium tin oxide (ITO)/CdS/Sb₂S₃/Au. This work provides a potential way to obtain vertically aligned thin films on different buffer layers.

Electric-field-dependent photoconductivity in CdS nanowires and nanobelts: exciton ionization, Franz-Keldysh, and Stark effects

We report on the electric-field-dependent photoconductivity (PC) near the band-edge region of individual CdS nanowires and nanobelts. The quasi-periodic oscillations above the band edge in nanowires and nanobelts have been attributed to a Franz-Keldesh effect. The exciton peaks in PC spectra of the nanowires and thinner nanobelts show pronounced red-shifting due to the Stark effect as the electric field increases, while the exciton ionization is mainly facilitated by strong electron-longitudinal optical (LO) phonon coupling. However, the band-edge transition of thick nanobelts blue-shifts due to the field-enhanced exciton ionization, suggesting partial exciton ionization as the electron-LO phonon coupling is suppressed in the thicker belts. Large Stark shifts, up to 48 meV in the nanowire and 12 meV in the thinner nanobelts, have been achieved with a moderate electric field on the order of kV/cm, indicating a strong size and dimensionality implication due to confinement and surface depletion.

Interferometric detection of spin-polarized transport in the depletion layer of a metal-GaAs Schottky barrier

It is shown that the Kerr rotation of spin-polarized electrons is modulated by the distance of the electrons from the sample surface. Time-resolved Kerr rotation of optically excited spin-polarized electrons in the depletion layer of n-doped GaAs displays fast oscillations that originate from interference between the light reflected from the semiconductor surface and from the front of the electron distribution moving into the semiconductor. Using this effect, the dynamics of the photogenerated charge carriers in the depletion layer of the biased Schottky barrier is measured.