http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

The dynamics and spectroscopy of silicon nanocrystals that emit at visible wavelengths were analyzed. Size-selective precipitation and size-exclusion chromatography cleanly separate the silicon nanocrystals from larger crystallites and aggregates and provide direct evidence for quantum confinement in luminescence. Measured quantum yields are as high as 50 percent at low temperature, principally as a result of efficient oxide passivation. Despite a 0.9—electron-volt shift of the band gap to higher energy, the nanocrystals behave fundamentally as indirect gap materials with low oscillator strength.

https://science.sciencemag.org/content/sci/262/5137/1242.full.pdf

Quantum confinement in size-selected, surface-oxidized silicon nanocrystals.

PHOTONIC devices are becoming increasingly important in information and communication technologies. But attempts to integrate photonics with silicon-based microelectronics are hampered by the fact that silicon has an indirect band gap, which prevents efficient electron-photon energy conversion. Light-emitting silicon-based materials have been made using band-structure engineering of SiGe and SiC alloys and Si/Ge superlattices, and by exploiting quantum-confinement effects in nanoscale particles and crystallites1–3. The discovery4,5 that silicon can be etched electrochemically into a highly porous form that emits light with a high quantum yield has opened up the latter approach to intensive study6–12. Here we report the fabrication, by molecular-beam epitaxy, of well-defined superlattices of silicon and SiO2, which emit visible light through photoluminescence. We show that this light emission can be explained in terms of quantum confinement of electrons in the two-dimensional silicon layers. These superlattice structures are robust and compatible with standard silicon technology.

Quantum confinement and light emission in SiO2/Si superlattices

Strong room-temperature photoluminescence (PL) in the wavelength range 650–950 nm has been observed in high temperature annealed (1000–1300 °C) substoichiometric silicon oxide (SiOx) thin films prepared by plasma enhanced chemical vapor deposition. A marked redshift of the luminescence peak has been detected by increasing the Si concentration of the SiOx films, as well as the annealing temperature. The integrated intensity of the PL peaks spans along two orders of magnitude, and, as a general trend, increases with the annealing temperature up to 1250 °C. Transmission electron microscopy analyses have demonstrated that Si nanocrystals (nc), having a mean radius ranging between 0.7 and 2.1 nm, are present in the annealed samples. Each sample is characterized by a peculiar Si nc size distribution that can be fitted with a Gaussian curve; by increasing the Si content and/or the annealing temperature of the SiOx samples, the distributions become wider and their mean value increases. The strong correlation betw...

Correlation between luminescence and structural properties of Si nanocrystals

We present a simple, linear‐in‐size method that enables calculation of the eigensolutions of a Schrodinger equation in a desired energy window. We illustrate this method by studying the near‐gap electronic structure of Si quantum dots with size up to Si1315H460(≊37 A in diameter) using a plane wave pseudopotential representation.

Solving Schrödinger’s equation around a desired energy: Application to silicon quantum dots

We have calculated the electronic structure of spherical silicon crystallites containing up to 2058 Si atoms. We predict a variation of the optical band gap with respect to the size of the crystallites in very good agreement with available experimental results. We also calculate the electron‐hole recombination time which is of the order of 10−4–10−6 s for crystallites with diameters of 2.0–3.0 nm. We conclude that small silicon crystallites can have interesting optical properties in the visible range. These results are applied to porous silicon for which we confirm that a possible origin of the luminescence is the quantum confinement.

J. P. Proot

Papers

Electronic structure and optical properties of silicon crystallites: Application to porous silicon

Electronic structure and optical properties of silicon crystallites