Zhenxu Lin

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.

Boron doped nanocrystalline silicon film characterization for solar cell application

Lightly doped hydrogenated amorphous silicon thin films were deposited through the plasma enhanced chemical vapor deposition (PECVD) technique using a gas mixture of SiH4, B2H6, and H2 as the precursor. By using thermal annealing at 800 and 1000°C, boron doped nanocrystalline silicon films were obtained. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of substitutional boron in the doped films. Based on the measurement of dark conductivity as a function of temperature, p-type nanocrystalline silicon (nc-Si:H) films with high room temperature conductivity and low active energy were observed. By using these p-type silicon films, P-N junction solar cells were prepared on the n-type nc-Si substrate. The device characteristics were investigated based on the measurements of the current-voltage and spectral-response.中文摘要本文采用等离子体增强化学气相沉积技术(PECVD)制备了轻度掺杂的氢化非晶硅薄膜, 沉积过程中以SiH4, B2H6 和 H2 的 混和气作为反应源. 原始淀积材料经过800和1000°C的高温热退火处理后, 形成了硼掺杂的纳米硅薄膜. X射线光电子能谱(XPS)显示硼 原子在薄膜中形成了替位式掺杂. 根据不同温度下暗电导率的测量结果, 轻度硼掺杂的纳米硅薄膜具有较高的室温暗电导率和较低的 激活能. 进而, 采用该种P型硅薄膜材料以N型单晶硅为基底, 制作了P-N结太阳能电池器件. 根据电流-电压特性以及光谱相应曲线的测 量分析, 对电池的性能特性进行了研究.

Multiple magnification effects of Ce 3+ ions on near-infrared persistent luminescence of Cr-doped LaAlO 3

Ce3+/Cr3+ co-doped LaAlO3 for near-infrared (NIR) long lasting phosphors were synthesized through solid-state reaction. Incorporation of Ce3+ ions into Cr3+-doped LaAlO3 significantly enhanced the NIR persistent luminescence by more than one order of magnitude compared with LaAlO3 doped with Cr3+. Detailed analysis of the photoluminescence, photoluminescence excitation, and Thermo-luminescence spectra, as well as the persistent decay behavior of Ce3+/Cr3+ co-doped LaAlO3, indicated that the improvement of NIR persistent luminescence at around 735 nm (Cr3+: 2E→4A2 transition) is not only originated from a persistent energy transfer process from Ce3+ ions to Cr3+ ions, but also attributed to the extra efficient traps created by incorporation of Ce3+ ions. The current work develops an alternative approach toward the efficient NIR Cr3+-doped non-gallate long-persistence phosphors.

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.

Defect Emission and Optical Gain in SiCxOy:H Films

Luminescent SiCxOy:H films, which are fabricated at different CH4 flow rates using the plasma-enhanced chemical vapor deposition (PECVD) technique, exhibit strong photoluminescence (PL) with tuning from the near-infrared to orange regions. The PL features an excitation-wavelength-independent recombination dynamics. The silicon dangling bond (DB) defects identified by electron paramagnetic resonance spectra are found to play a key role in the PL behavior. The first-principles calculation shows that the Si DB defects introduce a midgap state in the band gap, which is in good agreement with the PL energy. Moreover, the band gap of a-SiCxOy:H is found to be mainly determined by Si and C atoms. Thus, the strong light emission is believed to result from the recombination of excited electrons and holes in Si DB defects, while the tunable light emission of the films is attributed to the substitution of stronger Si-C bonds for weak Si-Si bonds. It is also found that the light emission intensity shows a superlinear dependence on the pump intensity. Interestingly, the film exhibits a net optical gain under ultraviolet excitation. The gain coefficient is 53.5 cm-1 under a pumping power density of 553 mW cm-2. The present results demonstrate that the SiCxOy system can be a very competitive candidate in the applications of photonics and optoelectronics.

Strong blue light emission from Eu-doped SiOC prepared by magnetron sputtering

The Eu-doped SiOC films were prepared by magnetron sputtering technique at a low temperature of 250°C. The effects of the Eu2O3 deposited power and post-thermal annealing temperature on the PL characteristics of the Eu-doped SiOC films were investigated. It is found that the photoluminescence intensity could be enhanced by more than tenfold by increasing the Eu2O3 deposited power from 20W to 80W. Furthermore, very bright blue light emission can be clearly observed with the naked eye in a bright room for the Eu-doped SiOC films prepared at a Eu2O3 deposited power of 80 W. The improved PL intensity is attributed to the increasing number density of europium silicate clusters as a result of the increasing Eu2O3 deposited power as well as high annealing temperatures.