Pressure-induced phase transition in porous silicon

High pressure studies of porous silicon reveal that a phase transition occurs at ∼170 kbar. The phase transition is detected by an abrupt change in color of porous silicon from orange-yellow to black. Photoluminescence measurements show an initial blue shift of the luminescence peak. At ∼25 kbar the blue shift ceases and a reversal of shift is observed. The red shift continues up to ∼90 kbar at which point the luminescence is quenched. The shift reversal is interpreted as a pressure-induced direct–indirect transition in porous silicon. The results are best explained in the context of the quantum confinement model.