Can Oxidation and Other Treatments Help Us Understand the Nature of Light-Emitting Porous Silicon?

Laser-induced greenish-blue photoluminescence of mesoporous silicon nanowires

Solid silicon nanowires and their luminescent properties have been widely studied, but lesser is known about the optical properties of mesoporous silicon nanowires (mp-SiNWs). In this work, we present a facile method to generate greenish-blue photoluminescence (GB-PL) by fast scanning a focused green laser beam (wavelength of 532 nm) on a close-packed array of mp-SiNWs to carry out photo-induced chemical modification. The threshold of laser power is 5 mW to excite the GB-PL, whose intensity increases with laser power in the range of 5–105 mW. The quenching of GB-PL comes to occur beyond 105 mW. The in-vacuum annealing effectively excites the GB-PL in the pristine mp-SiNWs and enhances the GB-PL of the laser-modified mp-SiNWs. A complex model of the laser-induced surface modification is proposed to account for the laser-power and post-annealing effect. Moreover, the fast scanning of focused laser beam enables us to locally tailor mp-SiNWs en route to a wide variety of micropatterns with different optical functionality, and we demonstrate the feasibility in the application of creating hidden images.

Near-Infrared Emission from a Porous Silicon Device

Visible to near-infrared emission is produced from a porous silicon device under current injection. The porous silicon emitter is fabricated by selectively under-etching a p-n junction. The device is rectifying when biased across the junction, and exhibits a region of negative differential resistance (NDR) at the higher current levels. Bright red-orange emission is observed along the length of the junction in forward bias, but most of the light is emitted in the near-infrared with a peak near 1.3 µm at 30 mA. The intensity of the visible component has an exponential dependence on photon energy. The optical and electrical properties of this device are presented and possible mechanisms are discussed.

The Visible and the Infrared Luminescence Bands as a Tool for Characterization of the Porous Silicon Bandstructure

The visible and the infrared photoluminescence bands in porous Si have been studied at low temperature for two series of samples: one in which the size of the crystallites has been varied and another in which the degree of surface degradation has been changed. It is shown that the relation of the two bands can be explored for characterization of the porous Si bandstructure. The size- and the surface dependence of the valence band and of the conduction band related states is discussed. A model is proposed for explanation.

Origin of the Infrared Band From Porous Silicon

The photoluminescence (PL) infrared (IR)-band of p-doped porous Si (PS) films is studied by steady-state and time-resolved PL and by photoluminescence excitation (PLE) in detail. In analogy to the S-band in the visible the IR-band shifts to higher energies with reduced average nanocrystal size. The IR- and S-bands are very different in their decay behavior and in their recombination lifetimes. The temperature-dependent PL intensity shows non-exponential decay with lifetime distributions in the nsec-µsec range in contrast to the stretched exponential decay shape of the S-band corresponding to lifetime distributions in the μsec -msec range. The origin of the IR-band is likely related to radiative recombination at deep defects in Si nanocrystals with quantum-upshifted band gaps.