Electrical band-gap energy of porous silicon and the band offsets at the porous-silicon/crystalline-silicon heterojunction measured versus sample temperature

Photocurrent measurements have been carried out on a series of samples consisting of porous silicon on top of crystalline silicon, in the temperature range 10–300 K. From the experimental data set, the electrical band-gap energy of porous silicon is deduced to be (1.8060.01) eV, independent of sample temperature. In contrast to this, some temperature variations are observed for the band offsets, reflecting qualitatively the temperature dependence of the fundamental band-gap energy of crystalline silicon. However, whereas the latter
decreases monotonically for increasing temperature, a maximum is observed at around 125 K for the conduction-band offset together with a corresponding minimum for the valence-band offset. The results are discussed with the conclusion that for the samples studied here, the electrical band gap in porous silicon is of a molecular nature and cannot be related to quantum-confinement properties of nanocrystals of elemental silicon.