Yanqing Guo

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.

Tunable red light emission from a-Si:H/a-SiN x multilayers

A tunable red photoluminescence from a-Si:H/a-SiNx multilayers was modulated in the wavelength range of 800–640 nm by controlling the thickness of the a-Si:H sublayer from 4 to 1.5 nm. Subsequent annealing was used to improve red photoluminescence without recrystallization of the amorphous silicon sublayers. The significant enhancement of red emission was found to depend on the decomposition of the Si–H bond in a-Si:H sublayers. Based on the absorption measurement, Raman, and FTIR spectra, the origin of light emission is ascribed to the silicon dangling bonds associated with hydrogen in a-Si:H sublayers, and the mechanism of light emission is suggested from the radiative recombination between the electrons existing at the negatively charged levels of silicon dangling bond and holes at the valence band.

Microstructure and initial growth characteristics of nanocrystalline silicon films fabricated by very high frequency plasma enhanced chemical vapor deposition with highly H2 dilution of SiH4

Nanocrystalline silicon (nc-Si:H) film deposited on silicon oxide in a very high frequency plasma enhanced chemical vapor deposition with highly H2 dilution of SiH4 has been investigated by Raman spectroscopy and high resolution transmission electron microscopy. It is found that at early growth stage the initial amorphous incubation layer in nc-Si:H growth on silicon oxide can be almost eliminated and crystallites with diameter of about 6 to 10 nm are directly formed on the silicon oxide. Nearly parallel columnar structures with complex microstructure are found from cross-sectional transmission electron microscopy images of the film. It is considered that highly H2 dilution and higher excitation frequency are the main reason for eliminating the initial amorphous incubation layer in nc-Si:H growth on silicon oxide.

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.