Review on the physicochemical treatments of rice husk for production of advanced materials

https://www.tandfonline.com/doi/pdf/10.1080/21870764.2018.1539210

Rice husk/rice husk ash as an alternative source of silica in ceramics: A review

Recent developments in the field of silicon nanostructures, particularly those properties and phenomena that are related to the photoluminescence (PL) from silicon nanostructures, have attracted much attention lately. A major source of controversy and disagreement among researchers is the underlying mechanism behind the PL. Two classes of models, i.e., the quantum confinement model that assigns the PL to quantum size effects in the nanocrystalline silicon core of the nanostructures and the surface chemistry model that assign the PL to surface phenomena at the interface between the crystalline core and the host matrix that wrap the nanostructures, are the most notable ones. In recent years, alternative structures to porous silicon, which allow synthesizing high quality silicon nanostructures with better control of their dimensionality, shape and size distribution, have emerged. In particular, fabrication techniques of silicon nanocrystals embedded in silicon-dioxide (SiO2) matrices have reached a level where consistent investigation of surface and quantum size phenomena can be performed. Recent experimental results and theories suggest that none of the above models alone can explain the entire spectrum of optical phenomena in silicon nanostructures. Instead, a refined model that takes into account the mutual role of quantum confinement and surface chemistry in shaping the optical properties of these nanostructures should be considered.

Photoluminescence from silicon nanostructures: The mutual role of quantum confinement and surface chemistry

Electrical devices based on Erbium (Er) doping of silicon nitride have been fabricated by reactive cosputtering and intense, room temperature Er electroluminescence was observed in the visible (527, 550, and 660 nm) and near-infrared (980 and 1535 nm) spectral ranges at low injection voltages (<5 V EL turn on). The electrical transport mechanism in these devices was investigated and the excitation cross section for the 1535 nm Er emission was measured under electrical pumping, resulting in a value (1.2×10−15 cm2) comparable to optical pumping. These results indicate that Er-doped silicon nitride has a large potential for the engineering of light sources compatible with Si technology.

/pdf/electroluminescence-from-er-doped-si-rich-silicon-nitride-3qmla7b9rl.pdf

Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes

Silicon nanocrystals (Si-nc) is an enabling material for silicon photonics, which is no longer an emerging field of research but an available technology with the first commercial products available on the market. In this paper, properties and applications of Si-nc in silicon photonics are reviewed. After a brief history of silicon photonics, the limitations of silicon as a light emitter are discussed and the strategies to overcome them are briefly treated, with particular attention to the recent achievements. Emphasis is given to the visible optical gain properties of Si-nc and to its sensitization effect on Er ions to achieve infrared light amplification. The state of the art of Si-nc applied in a few photonic components is reviewed and discussed. The possibility to exploit Si-nc for solar cells is also presented. In addition, nonlinear optical effects, which enable fast all-optical switches, are described.

http://diposit.ub.edu/dspace/bitstream/2445/15728/1/Navarro_2009%20X.pdf

Silicon Nanocrystals as an Enabling Material for Silicon Photonics

Thin film metal-oxide-semiconductor light emitting devices (LEDs) based on nanocrystalline silicon multilayer structure were grown by plasma-enhanced chemical vapor deposition. Room temperature electroluminescence was studied under direct current and time-resolved pulsed-current injection schemes. Multilayer LEDs operating at voltages below 5 V and electroluminescence turn-on voltage of 1.4–1.7 V are demonstrated. The turn-on voltage is less than 3.2 V which corresponds to the barrier height at the silicon oxide interface for electrons. Electrical injection in the multilayer LED is controlled by direct tunneling of electrons and holes among silicon nanocrystals. This injection regime is different than the Fowler–Nordheim tunneling that controls the electron injection in single thick layer LED operating at high voltages. A comparison of the power efficiency for the multilayer based LED and a similar single thick layer LED shows larger power efficiency for the former than for the second. Our results open ne...

Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers

In this paper, we present a room-temperature electroluminescence (EL) study of amorphous nonstoichiometric silicon nitride (SiNX) films. The light-emitting device is formed by an ITO/SiNX/p-type silicon structure. EL shows a yellowish broad emission spectrum with a power efficiency of 10−6. The EL peak energy depends on the bias voltage rather than on the silicon content in SiNX. By fitting the current-voltage characteristic with existing models, we found that under high voltages the Poole–Frenkel hole conduction is the main carrier transport mechanism in these devices. Injected electrons are captured by silicon dangling bonds (K center) and recombine with holes, which are localized in valence band tail states. Unbalanced hole and electron injection and nonradiative recombination are the main constraints on the EL efficiency of SiNX.

Light emission properties and mechanism of low-temperature prepared amorphous SiNX films. II. Defect states electroluminescence

A room-temperature photoluminescence (PL) study of amorphous nonstoichiometric silicon nitride (SiNX) films prepared under low temperature is reported. PL peak position can be tuned from 1.90 to 2.90 eV by adjusting the film composition. The luminescence lifetime is within the nanosecond range. The dependence of the PL lifetime on the emission energy suggests that band tail states are involved in the thermalization and recombination of photon-generated carriers. This is further supported by the correlation between the optical band gap, the PL peak energy, and the width of the PL spectrum. We propose that optical transitions among band tail states are the main light emission mechanisms.

Light emission properties and mechanism of low-temperature prepared amorphous SiNX films. I. Room-temperature band tail states photoluminescence

Recent results on the photoluminescence properties of silicon nanocrystals embedded in silicon oxide are reviewed and discussed. The attention is focused on Si nanocrystals produced by high-temperature annealing of silicon rich oxide layers deposited by plasma-enhanced chemical vapor deposition. The influence of deposition parameters and layer thickness is analyzed in detail. The nanocrystal size can be roughly controlled by means of Si content and annealing temperature and time. Unfortunately, a technique for independently fine tuning the emission efficiency and the size is still lacking; thus, only middle size nanocrystals have high emission efficiency. Interestingly, the layer thickness affects the nucleation and growth kinetics so changing the luminescence efficiency.

/pdf/photoluminescence-of-silicon-nanocrystals-in-silicon-oxide-wy75mc6poa.pdf

M. Wang

Papers

Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers

Light emission properties and mechanism of low-temperature prepared amorphous SiNX films. II. Defect states electroluminescence

Light emission properties and mechanism of low-temperature prepared amorphous SiNX films. I. Room-temperature band tail states photoluminescence

Photoluminescence of silicon nanocrystals in silicon oxide