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 te mperature range 10-300 K. From the experimental data set, the electric al band-gap energy of porous silicon is deduced to be (1.80 +/- 0.01) eV. independent of sample temperature. In contrast to this, some tempe rature variations are observed for the band offsets, reflecting qualit atively the temperature dependence of the fundamental band-gap energy of crystalline silicon. However, whereas the latter decreases monotoni cally 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 concl usion that for the samples studied here, the electrical band gap in po rous silicon is of a molecular nature and cannot be related to quantum -confinement properties of nanocrystals of elemental silicon. [S0163-1 829(98)06336-X].