Investigation of chemical adsorbate effects on blue and red emitting porous silicon samples

We have investigated the sensitivity of blue (PL_max = 480 nm) and red (PL_max = 660 nm) emitting porous silicon samples to various chemical adsorbates. Steady-state and time-resolved photoluminescence measurements and FTIR spectroscopy were employed to characterize the photophysical and optical effects induced by chemical exposure. The red samples, which are hydrogen terminated, exhibit quenching and recovery of photoluminescence intensity and broadening of the Si-H_X stretch bands upon exposure to liquid methanol. This behavior is attributed to the ability of the Si-H_X specie on the surface of the PSI to interact with the solvent molecules which temporarily traps the electrons and causes PL loss and Si-H_x broadening. The blue samples, which are oxygen terminated, display similar sensitivity to methanol. This sensitivity is attributed to the solvent's ability to change the surface passivation and thereby introduce competitive radiative and nonradiative recombination channels. The origin of the blue PL is discussed.