Time-Resolved Luminescence of Porous Si and InP

Abstract

The kinetics of porous Si and InP luminescence has been investigated using short (10 ps, 2 ns and 14 ns) laser pulses for excitation, by a streak camera with 10 ps time-resolution and photomultiplier for measuring fast and slow increase and decay of the intensity of luminescence. Two luminescence bands with fast and slow decay have been registered within the usually observed single wide band in the time-resolved photoluminescence spectra of porous Si and attributed to the recombination via free excitons and the surface states in nanostructures. The time-resolved intensity of porous InP luminescence has been measured at different intensities of laser excitation. At high excitation the intensity of photoluminescence has a relatively slow increase and complicated decay. The change of the kinetic properties has been explained by numerous processes in semiconductor±dielectric quantum wires and dots: the slowing down of intraband relaxation, collective exciton±exciton (electron) interaction, Auger recombination, etc.Introduction Porous silicon has attracted the most attention of all forms of silicon nanostructures because of its intense visible photoluminescence (PL) discovered in the pioneering work of Canham [1]. Numerous physical models have been proposed to explain the PL of porous Si: 1. optical transitions in the structures with quantum confinement (quantum wires and dots), 2. transitions via localized surface states, 3. PL of different chemical species (e.g., seloxenes). Recently it was shown [2] that depending on the size of Si nanostructures the PL of porous Si can be tuned from near infrared to the ultraviolet if the surface of the sample is passivated with Si±H bonds, and that in this case the recombination is via free exciton (electron±hole) states for all sizes. But after exposure to oxygen SiO bonds are formed and the PL shifts to the red by as much as 1 eV because new electronic trap states (the trapped electron state localized on the Si atom and the trapped hole state localized on the oxygen atom) appear in the band gap of smaller nanostructures. Thus, for porous Si exposed to oxygen it is difficult to distinguish the recombination that arises due to the free exciton transitions in nanostructures from the recombination via trapped excitons.The goal of this paper is to show that the time-resolved spectra of porous Si exposed to oxygen allow to distinguish the PL conditioned both by optical transitions in nanostructures (recombination via free exciton or electron±hole states) and the surface localized states.In contrast to Si, A 3 B 5 semiconductors have a direct gap. Investigation of porous direct gap semiconductors such as GaAs, GaP, InP allows to avoid the limitations of an indirect band gap in interpretation of their properties [3±5]. The anodization of InP

Microstructure and photoluminescence spectra of porous InP

“…The discrepancy is unclear at the moment. Chernoutsan et al observed PL emissions at 2.07 eV from porous InP (∼ 5 nm of the average size of InP nanostructures) formed in HCl [13]. Compared to their result, the PL blueshifted energy is smaller in our measurements.…”

Thermal diffusion in nanostructured porous InP

“…The PL peak positions observed in our experiment is consistent with the reported results (Chernoutsan et al 2000;Schmuki et al 2000). Figures 3 and 4 and table 2 also show that peak positions (corresponding peak energies) in all porous samples are blue shifted from the bulk InP whose PL peak is at 1⋅34 eV (Levinshtein et al 1996).…”