Appl. Phys. Lett. 100, 132106 (2012)
Precise control over the surface properties of semiconductor nanomaterials is essential for their use in many optoelectronic applications. Porous semiconductors are particularly appealing for use as biochemical sensors, owing to their large surface areas and high aspect ratios. Terahertz time-domain spectroscopy can be used to investigate electron transport in semiconductor nanomaterials, as long as the material's properties are not permanently changed by the photoexcitation. J. Lloyd-Hughes and co-workers have now shown that photoexcitation causes a quasi-permanent increase in the conductivity of a nanoporous InP honeycomb, with the conductivity remaining high for one hour after photoexcitation. The researchers used terahertz time-domain spectroscopy to measure the transmission of InP porous membranes with varying donor density and orientation, and employed X-ray photoemission spectroscopy to examine the charge density and composition of the surface states. The electron density varied for different surface pinning energies, which suggests that photoexcitation may reduce the density of the surface states. This effect could be useful in materials processing because it offers a clean, dry and area-selective way of quasi-permanently altering the conductivity of a porous semiconductor. However, the researchers stress that further work will be necessary to establish both the microscopic origin of the effect and its universality.
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