Papers by Keyword: Nanocrystalline Silicon

Abstract: Nanocrystalline silicon (nc-Si) thin film on glass substrate is subjected to excimer laser crystallized by varying the laser energy density in the range of 50~600 mJ/cm². The effect of excimer laser crystallization on the structure of silicon film is investigated using Raman spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. The results show that polycrystalline silicon thin films can be obtained by excimer laser crystallization of nc-Si films. A laser threshold energy density of 200 mJ/cm² is estimated from the change of crystalline fraction and surface roughness of the treated films. The growth of grain is observed and the crystallization mechanism is discussed based on the super lateral growth model. The nanocrystalline silicon grains in the films act as seeds for lateral growth to large grains.

Abstract: This paper reports the synthesis and characterization of silicon quantum dots (QDs) obtained by thermal annealing of hydrogenated amorphous silicon (a-Si:H)/silicon oxide (SiO₂) supperlattices deposited by plasma-enhanced chemical vapour deposition (PE-CVD). The as-deposited supperlattices have been annealed in high-temperature vacuum chamber, at temperatures up to 1100 °C, where in-situ phase transformation was monitored by x-ray diffractometry, XRD. It is shown that onset of crystallization and phase separation occur at different annealing temperature depending on the a-Si:H sub-layer thickness. Complete crystallization of the films and precipitation of the QDs occur at 1000 °C.

Abstract: High-efficiency solar cells based on amorphous silicon technology are designed. Multi-junction amorphous silicon solar cells are discussed, how these are made and how their performance can be understood and optimized. Although significant amount of work has been carried out in the last twenty-five years, the Staebler-Wronski effect has limited the development of a-Si:H solar cells. As an alternative material, nc-Si:H has attracted remarkable attention. Taking advantage of a lower degradation in nc-Si:H than a-Si:H and a-SiGe:H alloys, the light induced degradation in triple junction structures has been minimized by designing a bottom-cell-limited current mismatching, and obtained a stable active-area cell efficiency. All this has been investigated in this paper.

Abstract: In this paper, intrinsic nanocrystalline silicon thin films were deposited onto the ITO/glass substrates by PECVD and were used as the conduction material for the conductive-bridging random-access memory devices. The resistive switching characteristics of the nanocrystalline silicon thin films were investigated. Experimental results have shown that the stable bipolar resistive switching of the nc-Si films and retention time over 10⁴s. In addition, the current conduction mechanism of the nanocrystalline silicon films was examined with XPS depth file analysis. It clearly indicates that the conduction mechanism for the resistive switching is formation metallic bridges come form metal cation migration in the nanocrystalline silicon films.

Abstract: In recent years, hydrogenated nanocrystalline silicon (nc-Si:H) film has received much attention due to its potential application in various optoelectronic devices. In the present work, nanocrystalline silicon (nc-Si) films were fabricated from SiH4 diluted with H2 in very high frequency (40.68 MHz) plasma enhanced chemical vapor deposition system. The influence of radio frequency (rf) power on the structural properties of nanocrystalline silicon films has been studied. Raman spectra show that the crystallinity of the nc-Si films can be increased by promoting the rf power. But over high rf power leads to the structural deterioration of nc-Si:H film. AFM images manifest that, with the increase of deposition time, the grain size becomes larger accompanied by the decrease of the number density.

Abstract: Silicon thin film was successfully deposited on glass substrate using Radio frequency (RF) magnetron sputtering. The effect of deposition pressure on the physical and structural properties of thin films on the glass substrate was studied. The film thickness and deposition rate decreased with decreasing deposition pressure. Field emission scanning electron microscopy (FESEM) shows as the deposition pressure increased, the surface morphology transform from concise structured to not closely pack on the surface. Raman spectroscopy result showed that the peak was around 508 cm-1, showing that the thin film is nanocrystalline instead of polycrystalline silicon.

Abstract: Nanocrystalline silicon (nc-Si) thin films were deposited on glass and polytetrafluoroethylene (PTFE, teflon) substrates using Radio frequency (RF) magnetron sputtering. The effect of RF power and deposition temperature on the physical and structural properties of nc-Si on the glass and Teflon substrate was studied. The thin films properties were examined by Raman spectroscopy and field emission scanning electron microscopy (FESEM). We found that the thickness of thin films increased with increased RF power and deposition temperature. Raman spectroscopy results it showed that, with increasing RF power and deposition temperature can cause the changing of crystallinity on both glass and Teflon substrate.

Abstract: Boron-doped nanocrystalline silicon thin films(p-nc-Si:H) were deposited on glass substrates by plasma enhanced chemical vapour deposition (PECVD) using SiH₄ / H₂ / B₂H₆. The effects of substrate temperature, rf power and diborane flow on the microstructure, the electrical properties of nanocrystalline silicon thin films have been investigated. The results show that, increasing substrate temperature, rf power and B₂H₆ flow can improve the conductivity of P-Si thin film. However, exceeding one value, they are not advantageous to improve the conductivity due to the decrystallization of films. Hence, appropriate process conditions are crucial for the preparation of high quality p layer. crystalline volume fraction (Xc) 26.2 %, mean grain size (d) 3.5nm and conductivity 0.374S/cm, p-nc-Si:H thin film was deposited.

Abstract: A new tunnel-recombination junction model was proposed to increase the recombination of n/p junctions in tandem solar cells. According to the model, we fabricated a new tunnel junction with a nanostructured amorphous silicon p⁺ (na-Si p⁺) layer inserted between the n layer and the p layer. To compare with the conventional method, we fabricated another tunnel junction with an amorphous p⁺ (a-Si p⁺) insertion layer. Both devices were characterized by their dark current-voltage behavior (I-V), activation energy (E_a) and quantum efficiency (QE). The result shows that the tunnel junction with a na-Si p⁺ insertion layer has higher recombination rates with higher density of defect states of about 2.7×10¹⁹cm^-3 , lower resistance with activation energy of 22meV. The tunnel junction with a na-Si p⁺ insertion layer could be easily integrated into the tandem solar cell deposition process.

Abstract: Nanocrystalline silicon film has become the research hit of today’ s P-V solar technology. It’s optical band gap was controlled through changing the grain size and crystalline volume fraction for the quanta dimension effect. The crystalline volume fraction in nc-Si:H is modulated by varying the hydrogen concentration in the silane plasma. Also, the crystallinity of the material increases with increasing hydrogen dilution ratio, the band tail energy width of the nc-Si:H concurrently decreases. Two sets of nc-Si:H solar cells were made with different layer thicknesss, their electronic and photonic bandgap, absorption coefficient, optical band gap, nanocrystalline grain size(D), and etc have been stuied. In addition, we discussed the relationship between the stress of nc-Si thin films and H2 ratio. At last nc-Si:H solar cells have been designed and prepared successfully in the optimized processing parameters.