Description
Single-crystalline III–V semiconductor nanofilms are an intriguing but still underused device architecture. They use planar ultrathin films (<100 nm) as the active material, combining very high surface-to-volume ratios with minimal optical thickness. The high surface-to-volume ratio is attractive for sensing[1], while the reduced optical thickness enables photodetector designs where short-wavelength absorption is enhanced and longer-wavelength response is suppressed. This enables e.g. UV-sensitive photodetectors from GaAs and InP, despite their moderate near-infrared band gaps[2].
Here, we study InP nanofilms systematically, from quasi-2D 5 nm films to bulk-like 550 nm reference. Optically, the transmittance spectra are strongly thickness dependent. The nanofilms show room-temperature photoluminescence, indicating good surface quality, with a clear PL blueshift attritubed to quantum confinement. Electronically, the 550 nm film retains bulk-like behaviour, whereas the thinnest films show high resistivity and low estimated mobility, suggestive of hopping-mediated transport rather than conventional band transport. When implemented as photoconductors, however, the nanofilms produce extremely high on–off ratios, which we attribute to trap-state saturation that partially restores band transport under illumination. The devices also show useful responsivity, high UV-to-visible detection ratios, and fast response speeds. Owing to their ultralow thickness, the nanofilms remain functional under bending to a radius of only 2 mm, which is unusually small for inorganic semiconductors.
The ultrathin geometry also enables polarization-selective photodetection. In a simple photoconductor, polarization selectivity can be accessed by edge illumination, giving a dichroic ratio of ~4 in the UV-A region. In a more advanced approach, photonic crystals can be fabricated directly on the nanofilms to enhance absorption at selected wavelengths and polarizations. These results show that single-crystalline InP nanofilms provide a practical platform for miniaturized photodetectors, flexible devices, and monolithic polarization-selective spectrometers.
[1] Wei, S. et al. Energy & Environmental Materials 7, e12763 (2024)
[2] Haggren, T. et al. Nanoscale 18, 6011–6022 (2024)
| I am the presenting author | Yes |
|---|