Hengping Dong

Role of barrier layers in electroluminescence from SiN-based multilayer light-emitting devices

We report the effects of barrier layer on the electroluminescence properties of the SiN-based multilayer light-emitting devices (LEDs). It is found that the emission efficiency is significantly enhanced by more than one order of magnitude compared to that of LED without barrier layer. Meanwhile, the emission wavelength can also be tuned from 620to510nm by controlling the Si∕N ratio of the barrier layer. The improved performance of LEDs can be attributed to the variation in the band offset between the Si-rich SiN well layer and the N-rich SiN barrier layer.

Strong green-yellow electroluminescence from oxidized amorphous silicon nitride light-emitting devices

High efficiency luminescent amorphous silicon nitride films grown at room temperature with subsequent plasma oxidation were used as the active layers in the electroluminescent devices. A strong uniform green-yellow light emission from the devices was realized under forward biased conditions. It was found that the turn-on voltage could be reduced to as low as 6V while the electroluminescence (EL) intensity is significantly enhanced by two to four times by using p-type Si anode instead of indium tin oxide substrate under the same forward voltage. Furthermore, the EL peak position is blueshifted from 560to540nm, which is more close to that of the corresponding photoluminescence peak. The origin of light emission is suggested to be the same kind of luminescent centers related to the Si–O bonds.

Enhanced electroluminescence efficiency of oxidized amorphous silicon nitride light-emitting devices by modulating Si/N ratio

The authors had reported green-yellow electroluminescence (EL) from N-rich oxidized amorphous silicon nitride (a-SiN:O) light-emitting devices (LEDs) in a previous work. In this work, a significantly enhanced EL intensity was obtained in the LED by employing Si-rich a-SiN:O instead of N-rich a-SiN:O as luminescent active layer. Moreover, the Si-rich a-SiN:O devices also exhibit lower turn-on voltage and the external quantum efficiency is found to be three times higher than that of the N-rich a-SiN:O devices. The electrical characteristics analyses reveal that the injection barrier for Si-rich a-SiN:O devices is reduced by 30% compared to that of N-rich a-SiN:O devices, which results in a remarkably enhanced carrier-injection efficiency and gives rise to the notable improved performances of the LEDs.

Reflectivity behavior of two-dimensional ordered array of metallodielectric composite particles at large incidence angles

Optical reflectance of a two-dimensional (2D) metallodielectric (MD) photonic crystal composed of hexagonal array of close-packed silver-shell polystyrene-core composite particles has been studied at off-normal incidence under both P and S polarizations. A dramatic change in reflectivity behavior of the 2D MD film from a 2D colloidal crystal template and a homogeneous silver film has been observed. The phenomenon of strong reflectance bands of the 2D MD film was explained as a selective coupling of the incident light with surface plasmon of the 2D textured structure via the 2D grating.

Field dependent electroluminescence from amorphous Si/SiNx multilayer structure

We report field dependent electroluminescence (EL) from as-deposited amorphous Si/SiNx multilayer structure, where a-Si well layer thickness ranges from 1 to 4 nm, while SiNx barrier layer thickness is fixed at 3 nm. When the sample is applied by a low forward voltage Vbias ( 6 V), another EL band at the higher energy region is observed to be peaked at about 530 nm, which is independent of the well layer thickness. Photoluminescence (PL) investigation performed under optically pumped by the 325 nm line and the 488 nm line, respectively, also demonstrates the pump energy dependence of PL peaks. We interpreted these interesting phenomena of electrical and optical pump energy dependence of light emission by using different luminescence mechanisms in the a-Si/SiNx multilayer structure.

Higher than 60% internal quantum efficiency of photoluminescence from amorphous silicon oxynitride thin films at wavelength of 470 nm

We reported the study on the photoluminescence internal quantum efficiency (PL IQE) and external quantum efficiency (PL EQE) from the amorphous silicon oxynitride (a-SiNO) films, which were fabricated by plasma-enhanced chemical vapor deposition followed by in situ plasma oxidation. We employed the direct measurement of absolute quantum efficiency within a calibrated integration sphere to obtain the PL EQE. Then, we calculated the PL IQE by combing the measured EQE and optical parameters of light extraction factor, reflectivity, and transmittance of the a-SiNO thin films. We also derived the PL QE through investigating the characteristic of the temperature dependent PL. These results show that the PL IQE as high as 60% has been achieved at peak wavelength of about 470 nm, which is much higher than that of Si nanocrystal embedded thin films.

The evolution of photoluminescence in oxidized amorphous silicon nitride films by rapid thermal annealing

The influence of rapid thermal annealing on the photoluminescence (PL) properties of oxidized amorphous silicon nitride (a-SiN : O) films fabricated at a low temperature was investigated. The PL intensity from the annealed samples is found to be significantly enhanced by the RTA treatment when the temperature increases from 400 to 900 °C, while the PL peak position is shown to gradually move from the green to the red region. By combining the PL red-shift with the analysis of the film structure evolution, the origin of the red-shifted PL is suggested to be from a-Si nanoparticles, while the enhanced PL intensity is attributed to the increase in the a-Si nanoparticle density in the a-SiN : O films where the quantum confinement effect plays an important role. The present results strongly indicate that the RTA treatment is an effective way of fabricating tunable high-efficiency light-emitting devices.

Enhanced electroluminescence from nc-Si/SiO 2 pillar arrays using nanosphere lithography

Intensive electroluminescence could be observed from nc-Si/SiO2 pillars. The electroluminescence intensity is increased by 30 times of magnitude compared to that of nc-Si/SiO2 multilayers. The enhancement of EL can be attributed to the improved extraction efficiency of emission light and the high carrier-injection efficiency.

Enhanced blue-orange-red light emission from nc-Si:H/SiO2 pillar arrays using nanosphere lithography

Hydrogen passivated nanocrystalline Si/SiO2 (nc-Si:H/SiO2) pillar arrays were fabricated by using nanosphere lithography combination with hydrogen plasma annealing (HPA). Enhanced blue-orange-red photoluminescence (PL) could be observed by the naked eye in the bright room from the samples. By controlling the size of nc-Si:H from 3.8 to 1.8 nm, the PL peak blueshifts from 757 to 435 nm. It is found that the nanopillar structure can drastically enhance the light-absorbing properties of the samples and hydrogenation of nc-Si embedded in pillars is benefit to the increase of photoluminescence (PL) intensity. Combined with the analysis of atomic force microscope (AFM), transmission electron microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy and absorption spectra, the blue photoluminescence (PL) peak are ascribed to the quantum size effect of the nc-Si passivated by hydrogen, and the orange and red ones to both the localized surface states and quantum confinement effects of nc-Si:H. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Intense green light emission from low temperature grown SiNO complex system

We report intense green photoluminescence from amorphous oxidized silicon nitride film (a-SiN:O). A-SiN:O light-emitting devices of green-yellow color are successfully fabricated. Notably, EL efficiency can be significantly enhanced by modulating Si/N ratio in luminescent active layer.