Kunji Chen

Visible photoluminescence in crystallized amorphous Si:H/SiNx:H multiquantum‐well structures

Visible photoluminescence has been observed in crystallized a‐Si:H/a‐SiNx:H multiquantum‐well structures at room temperature. The MQW heterostructures consisting of 72 layers were formed by computer controlled plasma‐enhanced chemical‐vapor deposition method and then crystallized by Ar+ laser annealing technique. The crystallinity and average grain size of the silicon microcrystals were determined by means of Raman and x‐ray diffraction spectroscopy. The crystallized samples with well‐layer thickness Ls=40 A showed an intense photoluminescence which is peaked at 2.1 eV with a full width at half‐maximum of 0.25 eV. This is consistent with calculations based on the quantum confinement model.

Observation of the size-dependent blueshifted electroluminescence from nanocrystalline Si fabricated by KrF excimer laser annealing of hydrogenated amorphous silicon/amorphous-SiNx:H superlattices

Nanocrystalline silicon (nc-Si) was fabricated by KrF excimer laser annealing of hydrogenated amorphous silicon/amorphous-SiNx:H superlattices. A stable and reproducible electroluminescence (EL) based on these structures was observed at room temperature. It was found that the EL peak was significantly blueshifted from 780 to 600 nm with decreasing the a-Si:H sublayer thickness from 4.0 to 1.0 nm, while the intensity was also notably enhanced. The results suggest that the quantum confinement effect may play an essential role in visible light emissions from our present samples.

Full color light emission from amorphous SiCx:H with organic–inorganic structures

Hydrogenated amorphous silicon carbide films with an organic–inorganic compound structure were fabricated by using organic carbon source xylene (C8H10), in a traditional radio frequency plasma-enhanced chemical vapor deposition system. Strong full-color light emission ranging from 630 to 420 nm was observed at room temperature. The results of photoluminescence and photoluminescence excitation experiments showed the emission was originated from the radiative recombination at band tails of the inorganic SiC matrix. Moreover, luminescence from the transition between discrete energy levels, which were associated with organic π-conjugated carbon systems, was also observed at resonant excitation conditions.

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.

Resistive switching mechanism in silicon highly rich SiOx (x < 0.75) films based on silicon dangling bonds percolation model

The unipolar resistive switches are investigated in silicon highly rich SiOx (x   1.8) based devices, our Pt/SiO0.73/Pt devices operate at lower voltage regime (<2.0 V) and exhibit much lower resistance (∼30 Ω). The reset voltage (∼0.7 V) is lower than set voltage (∼1.7 V) and the performance is reduced in the vacuum environment. We propose a Si-DBs percolation model to explain the above characteristics. The experimental evidences for supporting our model are presented and discussed.

Visible light emission from single layer Si nanodots fabricated by laser irradiation method

A single layer of dense (>1011cm−2) Si nanodots on an insulating a-SiN layer was fabricated by the method combining the laser irradiation on the ultrathin amorphous Si films and subsequent thermal annealing. Raman scattering spectroscopy, planar and cross-section transmission electron microscopy were employed to characterize the formation of Si nanodots. It was found that the size of formed Si nanodots is strongly influenced by the initial amorphous Si film thickness. Visible light emission was observed from the obtained Si nanodots at room temperature and the luminescence peak is varied from 660to725nm with increasing the amorphous Si film thickness. The variable luminescence can be attributed to the interface state assisted radiative recombination rather than the quantum size effect.

Enhancement of band-edge luminescence and photo-stability in colloidal CdSe quantum dots by various surface passivation technologies

Gelatin stabilized and AOT (sodium dioctyl sulfosuccinate) coated colloidal CdSe quantum dots (QDs) have been synthesized in aqueous solution and in micelle solution respectively. Photoluminescence spectra studies show that comparing to gelatin stabilized CdSe QDs, organic AOT stabilized CdSe QDs exhibit an enhancement of band-edge luminescence due to the surface passivation. We also use a higher band gap inorganic CdS for passivating layer on the core CdSe QDs. Our results indicate that CdSe/CdS QDs system shows both higher band-edge luminescence yield and greater stability under light illumination.

Size-dependent electroluminescence from Si quantum dots embedded in amorphous SiC matrix

Si quantum dots (QDs) were formed by thermal annealing the hydrogenated amorphous silicon carbide films (a-SiCx:H) with different C/Si ratio x, which were controlled by using a different gas ratio R of methane to silane during the deposition process. By adjusting x and post annealing temperature, the QD size can be changed from 1.4 to 4.2 nm accordingly, which was verified by the Raman spectra and transmission electron microscopy images. Size-dependent electroluminescence (EL) was observed, and the EL intensity was higher for the sample containing small-sized Si QDs due to the quantum confinement effect (QCE). The EL peak energy as a function of the Si QDs size was in good agreement with a modified effective mass approximation (EMA) model. The calculated finite barrier potential of the Si QDs embedded in SiC matrix is 0.4 and 0.8 eV for conduction and valence band, respectively. Moreover, the current-voltage properties and the linear relationship between the integrated EL intensity and injection current i...

Oxygen induced strong green light emission from low-temperature grown amorphous silicon nitride films

Luminescent amorphous silicon nitride films were fabricated by plasma-enhanced chemical vapor deposition at room temperature followed by thermal oxidation at 100°C. Very bright green emissions were clearly observed with the naked eye in a bright room after the samples had been oxidized. The emission peak is located at 495nm. Fourier-transform infrared absorption spectra and results of depth profiling with x-ray photoelectron spectroscopy indicate that the introduction of oxygen is of a key role in enhancing the photoluminescence intensity of the films. Emission and excitation spectra analyses suggest that the green emission is originated from the radiative recombination in the localized states related to the Si–O bonds.