The surface photovoltage (SPV) mechanism of a silicon nanoporous pillar array (Si-NPA) is investigated by using SPV spectroscopy in different external electric fields. Through comparisons with the SPV spectrum of single crystal silicon (sc-Si), the silicon nano-crystallite (nc-Si)/SiO𝑥 nanostructure of Si-NPA is proved to be capable of producing obvious SPV in the wavelength range 300-580 nm. The SPV for the sc-Si layer and the nc-Si/SiO𝑥 nanostructure has shown certain contrary characters in different external electric fields. Through analysis, the localized states in the amorphous SiO𝑥 matrix are believed to dominate the SPV for the nc-Si/SiO𝑥 nanostructure.

We report the electronic transition mechanisms for hydrothermally prepared silicon nanoporous pillar array (Si-NPA), investigated by surface photovoltage (SPV) spectroscopy and photoluminescence (PL) spectroscopy. By comparing the SPV spectra of single crystal silicon (sc-Si) with that of Si-NPA, the silicon nano-crystallites (nc-Si)/SiOx nanostructure in the Si-NPA could produce SPV in the wavelength range of 300–580 nm. And 580 nm (∼2.14 eV) was considered as the absorption edge of the nc-Si/SiOx nanostructure. After the sample was annealed and oxidized in air at different temperatures, both the SPV in the wavelength range of 300–580 nm and the PL emission band around 690 nm from the nc-Si/SiOx nanostructure weakened and disappeared as the annealing temperature increased from 100 to 500 °C. But both the red-infrared PL band (>710 nm) and the violet-blue PL band were enhanced by increasing the annealing temperature. After 2 years of natural oxidation in air, the SPV features for sc-Si disappeared completely, and the SPV characteristics of the nc-Si/SiOx nanostructure could be clearly observed. After analysis, the Si–O structure related localized states at the nc-Si/SiOx interface dominated the electronic transitions during the red PL emission and the SPV for the nc-Si/SiOx nanostructure in Si-NPA, the red–infrared PL was due to the Si=O structure related electronic transitions, and the violet-blue PL emission could attribute to the oxygen-related defect related recombination of the photo induced carriers.

A series of silicon nanoporous pillar array (Si-NPA) samples are prepared with different times of hydrothermal etching, and their surface morphologies are characterized. A systematic study on the evolution trend of the surface photovoltage and photoluminescence spectra discloses that the adoption of a prolonged etching time will increase the native degree of oxidation and decrease the interfacial states density localized in the SiO𝑥 matrix. These results might be helpful for designing Si-NPA-based semiconductor nanosystems with optimized physical properties.