Time resolved photoluminescence of porous silicon: Evidence for tunneling limited recombination in a band of localized states

Abstract

Time resolved photoluminescence of porous silicon at room temperature was measured for several emission energies under 2 ns nitrogen laser excitation. For each emission energy studied there is a broad distribution of lifetimes extending over a few decades. The mean value of the distribution varies with the emission energy, from 3 (2.77 eV) to 50 μs (1.96 eV). The results can be explained by assuming a tunneling limited recombination mechanism between bands of localized states. We associate this behavior with a superficial disordered Si:O:H compound rather than with quantum confinement effects.

Direct observation of oxygen-induced luminescent states in porous silicon by tunable excitation time-resolved spectroscopy

“…The PL decay time is ϳ4 ns which is similar to decay times reported by other groups. [6][7][8][9][10][11] It should be noted that the LEB with the decay of microsecond order seen in Fig. 2͑b͒ is not observed.…”

“…4 -7 Experimental results of steady-state PL and timeresolved PL ͑TRPL͒ in oxidized PS show a broad emission band located around 2.0 eV with decay times of microsecond order and an additional band located around 2.7 eV with decay times of nanosecond order, respectively. [6][7][8][9][10][11] In this letter, we report on tunable-excitation TRPL spectroscopy in which excitation of carriers to selective energy levels and subsequent carrier relaxation provides a clearer understanding of the carrier dynamics in oxidized PS. The carrier recombination processes via oxygen-induced luminescent states have been observed over a time scale from ns to ms as a function of excitation photon energy.…”

Carrier dynamics in oxidized porous silicon

“…The PL decay time is approximately 6 ns, which is similar to other reports. 6,7,9,[14][15][16] The PL peak energy position is located around 2.53 and 2.36 eV under 400 and 530 nm excitation, respectively. The PL peak energy position strongly depends on excitation photon energy, that is, over the excitation wavelength range 400-590 nm the PL peak energy position shifts from 2.53 to 2.07 eV.…”

“…9,[11][12][13] Both emission bands are also characterized by different luminescent decay rates. The HEB exhibits an extremely fast decay of several nanoseconds whereas the LEB is associated with three orders of magnitude slower decay times of approximately 10 s. 6,7,[14][15][16] It is, therefore, necessary to understand in detail both steady-state and time-resolved PL ͑TRPL͒ properties over the nanosecond to microsecond time scale, which will then provide an essential insight into the luminescence mechanisms in oxidized PS.…”

Carrier density and confined polaron effects in the photoluminescence of fresh and oxidized porous silicon

“…However, the emission shows a strong dependence on the adsorbed surface species and deviations from the quantum confinement model, so the quantum confinement model was modified to include the localized excitons 7 or surface states, 5 excited chemical species such as silicon hydride SiH x , 8,9 siloxene Si 6 O 3 H 6 derivatives 10 and silanones containing Si O. 11 Moreover, emissions from amorphous sites such as a-Si : H 12,13 or a-Si : O : H were also indicated, 14 therefore it is necessary to distinguish or verify such complicated models.…”