Structural parameters effect on the electrical and electroluminescence properties of silicon nanocrystals/SiO₂ superlattices

Abstract

The effect of the oxide barrier thickness (tSiO2) reduction and the Si excess ([Si]exc) increase on the electrical and electroluminescence (EL) properties of Si-rich oxynitride (SRON)/SiO2 superlattices (SLs) is investigated. The active layers of the metal–oxide–semiconductor devices were fabricated by alternated deposition of SRON and SiO2 layers on top of a Si substrate. The precipitation of the Si excess and thus formation of Si nanocrystals (NCs) within the SRON layers was achieved after an annealing treatment at 1150 °C. A structural characterization revealed a high crystalline quality of the SLs for all devices, and the evaluated NC crystalline size is in agreement with a good deposition and annealing control. We found a dramatic conductivity enhancement when the Si content is increased or the SiO2 barrier thickness is decreased, due to a larger interaction of the carrier wavefunctions from adjacent layers. EL recombination dynamics were studied, revealing radiative recombination decay times of the order of tens of microseconds. Lower lifetimes were found at higher [Si]exc, attributed to exciton confinement delocalization, whereas intermediate barrier thicknesses present the slowest decay. The electrical-to-light conversion efficiency increases monotonously at thicker barriers and smaller Si contents. We ascribe these effects mainly to free carriers, which enhance carrier transport through the SLs while strongly quenching light emission. Finally, the combination of the different results led us to conclude that tSiO2 ∼ 2 nm and [Si]exc from 12 to 15 at% are the ideal structure parameters for a balanced electro-optical response of Si NC-based SLs.

Effect of Si3N4‐Mediated Inversion Layer on the Electroluminescence Properties of Silicon Nanocrystal Superlattices

“…In the case of our device NC , the mentioned voltage pulse conditions led to the estimation of PE NC ≈ 6 × 10 −3 %, whereas the utilization of the Si 3 N 4 inversion layer (i.e., device NC‐SN ) induced an emission enhancement up to PE NC‐SN ≈ 2.6 × 10 −2 %, i.e., of a factor ≈4. This result is so far the maximum efficiency reached by our Si NC‐based devices . Please note that the PE enhancement after Si 3 N 4 inversion layer incorporation is notably larger than the one observed in the EL spectra (by a factor of ≈2).…”

“…Indeed, these curves already state a signature for each device structure. In particular, device NC shows an increase of current density of several orders of magnitude, as expected from continuous charge transport within NC‐related states and no blocking layer impeding charge injection through the electrodes . Device NC‐SN exhibits an analogous trend to device NC , which reveals similar carrier injection conditions.…”

Size‐Controlled Si Nanocrystals Fabricated by Electron Beam Evaporation

“…On one hand, the control of the Si NC size has been achieved by the Si NCs/SiO 2 multilayers (MLs) approach, where the stoichiometric SiO 2 layers play the role of barrier against Si diffusion, thus limiting the growth of the Si NCs along the vertical direction . In addition, several works on the effect of the annealing temperature ( T a ) and the thickness of the SiO 2 barriers have been carried out to determine the optimal structure for optoelectronic applications . On the other hand, the fabrication of these nanostructures has basically been achieved by means of either chemical‐vapor deposition, sputtering, or Si implantation in SiO 2 .…”

Modulation of the electroluminescence emission from ZnO/Si NCs/p-Si light-emitting devices via pulsed excitation

“…Notwithstanding, the asymmetry of electrons and holes in tunneling through SiO 2 barriers often leads to a less efficient excitation via impact ionization. 7,8 To overcome limitations of DC excitation, pulsed emission was proposed that relies on the efficient sequential injection of electrons and holes into NCs, [9][10][11][12] effectively lowering operation voltages and hence increasing device stability. 13 Considering the top contact, n-type poly-Si is typically employed for Si NC-based capacitors or field-effect transistors, 5,6,9 because it provides excellent charge injection and can be deposited and implanted via standard microelectronics techniques.…”

“…14 Therefore, wide-band gap n-type transparent conductive oxides (TCOs) such as indium tin oxide (ITO) are increasingly being used in these light-emitting systems. 7,8 In the present work, atomic layer deposition (ALD) of zinc oxide (ZnO) was used for the top contact, which is a robust alternative for Si NCs-based LEDs. 15,16 In addition, ALD-ZnO presents luminescence properties under certain fabrication conditions and device design, 16,17 which could be used to complement the redinfrared NCs-based emission towards higher energies within the visible spectrum.…”