Zewen Lin

Bright red, orange-yellow and white switching photoluminescence from silicon oxynitride films with fast decay dynamics

Strong tunable photoluminescence (PL) from silicon oxynitride materials have been demonstrated by modulating the oxygen content. The increase of oxygen content in the films from 8% to 61% results in red, orange-yellow and white switching PL. The change in PL characteristics of these films is ascribed to the variation of defect luminescent centers as well as the evolution of dominant phase structures changing from silicon nitride to silicon oxynitride and silicon oxide. The intense PL intensity is suggested from the nanoseconds recombination lifetime as well as the alleviation of internal stress in silicon oxynitride.

Suppression of Hole Overflow and Enhancement of Light Emission Efficiency in Si Quantum Dots Based Silicon Nitride Light Emitting Diodes

We present an effective method to suppress the hole overflow in Si quantum dots-based silicon nitride (SiN) light-emitting diodes (LEDs) by employing nanocrystalline Si (nc-Si) layer as hole blocking layer inserted between the SiN luminescent active layer and p-Si anode. The proposed devices exhibit strong white light emission under forward bias conditions. In comparison to the LEDs without nc-Si interlayer, a significant enhancement of more than 200% in light emission efficiency is achieved from the proposed devices. The increment in EL efficiency is found to strongly depend on the thickness of nc-Si interlayer. Besides, the proposed devices show a low turn-on voltage of 6 V, which is the same as that of the device without nc-Si interlayer. The analysis of the dominant recombination process indicates that the improved emission efficiency is resulting from the increased bimolecular radiative recombination probability, which is attributed to the effective hole-blocking effect of nc-Si barrier that mitigates the unbalance injections between electrons and holes in the SiN active layer by suppressing hole overflow.

Near-infrared light emission from Si-rich oxynitride nanostructures

Near-infrared (NIR) luminescent Si-rich oxynitride nanostructures were fabricated by very high frequency plasma enhanced chemical vapor deposition followed by thermal annealing. By increasing the annealing temperature from 600 °C to 1100 °C, the intensity of NIR emission can be remarkably improved by more than three times. Si nanocrystals (NCs) with diameters ranging from 2 nm to 4 nm are found to play a decisive role in the enhanced NIR emission. The PLE spectra indicate a band-to-band excitation process with a quantum confinement feature in Si nanocrystals. Combining with the infrared absorption spectra and X-ray photoelectron spectra analyses, it is suggested that the photoexcited carriers for the enhanced NIR emission mainly originate in the quantum confined Si NCs, while their radiative recombination occurs in the surface states related to N-Si-O bonds.

Efficiency enhancement for SiN-based light emitting device through introduction of Si nanocones in emitting layer

Silicon nitride-based light-emitting devices were fabricated with a SiNx emitting layer grown on annealed Si film of dense nano-crystalline cones. Comparative studies revealed that the patterned SiNx emitting layer, with embedding nanocrystalline Si cones and a rough surface morphology of its own, manifests a much enhanced, even doubled at sufficiently large injected current density, electroluminescence efficiency. Both the increased light-extraction capability and the effective hole-blocking by the presence of Si nanocones, the latter is favorable for the balance of carrier injection in emitting layer, are responsible for this remarkable efficiency enhancement. The current work established an alternative approach toward the fabrication of more efficient SiN-based light-emitting devices.

Improved power efficiency in phosphorus doped n-a-SiNxOy/p-Si heterojunction light emitting diode

The higher up to 60% internal quantum efficiency of photoluminescence (PL) from amorphous silicon oxynitride (a-SiNxOy) films has been reported in our previous work. In present work, the improved power efficiency visible light emitting diode (LED) has been realized based on phosphorus doped n-a-SiNxOy/p-Si heterojunction structure, which is at least three times higher than that of ITO/a-SiNxOy/p-Si (called MIS) LED. The n-a-SiNxOy films were doped by using phosphine (PH3) gas during the deposition by plasma enhanced chemical vapor deposition technique and the electron concentration is about 2.4 × 1015 cm−3 at room temperature obtained from Hall-effect measurements. The light emitting (electroluminescence (EL)) peak energy is coincided with that of PL of a-SiNxOy, which suggests that the EL emission is also originated from the radiative recombination via N-Si-O bonding defect states in n-a-SiNxOy layers. The transport mechanism and optical performance of the device have been investigated with the character...

Enhanced Electroluminescence From Si Quantum Dots-Based Light-Emitting Devices With Si Nanowire Structures and Hydrogen Passivation

Enhanced electroluminescence (EL) has been achieved from the light-emitting devices containing Si quantum dots/SiO2 multilayers deposited on Si nanowire arrays because of the good antireflection characteristics of Si nanowire structures, which improves the light extraction efficiency. However, it is found that the EL is first enhanced with increasing the depth of the Si nanowires and then reduced to further increase the depth, though it exhibits the lowest reflectance (~3%), which may be due to the increased surface defect states after long time etching, as revealed by electron spin resonance measurements. It is demonstrated that the posthydrogen plasma annealing treatments can passivate the surface defect states which, in turn, improve device performance. The best device shows the turn-on voltage as low as 3.5 V, and the EL intensity of devices on Si nanowire arrays is enhanced 16-fold, compared with that of flat one.