Co-reporter:Yang Ji;Yingying Zhai;Huafeng Yang;Jingjing Liu;Wenyi Shao;Wei Li;Kunji Chen
Nanoscale (2009-Present) 2017 vol. 9(Issue 41) pp:16038-16045
Publication Date(Web):2017/10/26
DOI:10.1039/C7NR05694J
Si quantum dot-based light emitting devices were fabricated on Si nanowire arrays in order to improve light extraction efficiency. However, the device performance is deteriorated by using Si nanowires with a depth of 1.2 μm due to serious surface recombination. By introducing an Al2O3 thin layer between the Si quantum dots and Si nanowires, significantly enhanced electroluminescence (∼8.5 fold) has been demonstrated. Based on electron spin resonance, capacitance–voltage and conductance–voltage measurements, the effect of the Al2O3 thin layer on the improvement of device performance is quantitatively evaluated. Our results demonstrate that besides the chemical passivation to reduce the surface defect states of Si nanowires, the Al2O3 thin layer can act as a barrier layer to confine the injected carriers in the active Si quantum dot layer due to the existence of negatively fixed charges and a potential barrier. As a consequence, radiative recombination is promoted which contributes to the enhanced light emission from devices based on Si quantum dot/Si nanowire hetero-structures.
Co-reporter:Yangqing Wu, Yang Ji, Jun Xu, Jingjing Liu, ... Kunji Chen
Acta Materialia 2017 Volume 131(Volume 131) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.actamat.2017.04.013
NaYF4:Yb,Er nanocrystals with different structures and sizes have been synthesized via a hydrothermal method. Structures and sizes of the NaYF4:Yb,Er nanocrystals are carefully investigated by changing the Gd3+ ion concentrations and reaction temperatures. It is found that the change of Gd3+ doping concentration and reaction temperature not only induces the phase transition but also causes the size difference. The introduction of Gd3+ ions can promote the phase change from cubic to hexagonal structures, which exhibit the different morphologies (nanoparticle vs nanorods). However, by increasing the reaction temperature slightly, the hexagonal structures can be formed with very low or even without any Gd3+ ions. It is shown that the enhanced up-conversion emission can be achieved by well controlling the Gd3+ ion concentrations at the certain reaction temperature to get the pure nanorods structures with suitable sizes.Download high-res image (145KB)Download full-size image
Co-reporter:Dan Shan, Yang Ji, Dongke Li, Jun Xu, Mingqing Qian, Ling Xu, Kunji Chen
Applied Surface Science 2017 Volume 425(Volume 425) pp:
Publication Date(Web):15 December 2017
DOI:10.1016/j.apsusc.2017.07.011
•The carrier mobility in Si nano-crystals(NCs) is significantly enhanced after P doping.•The barrier height of grain boundaries in SiNCs films can be reduced by P doping.•Surface defects statesin Si NCs films can be well-passivated by P doping.Usually, the conductivity of semiconductor can be increased after phosphorus (P) doping but the electron mobility will be obviously reduced due to the strong impurity scattering. Here, we report a novel phenomenon that the carrier mobility in Si nano-crystals is significantly enhanced after nanoscale P doping. It is found that the electron mobility reaches to 30.3 cm2/V s, which is improved by one order of magnitude compared with that of un-doped one (1.6 cm2/V s), while the room temperature conductivity is as high as 1.5 × 103 S/cm by appropriately P doping. The clear experimental evidences are present to demonstrate that both the reduction of barrier height of grain boundaries and the surface defects states due to P doping improve the corresponding electron mobility in nano-crystalline Si films.Download high-res image (171KB)Download full-size image
Co-reporter:Mingkun Xu, Zhaoguo Xue, Jimmy Wang, Yaolong Zhao, Yao Duan, Guangyao Zhu, Linwei Yu, Jun Xu, Junzhuan Wang, Yi Shi, Kunji Chen, and Pere Roca i Cabarrocas
Nano Letters 2016 Volume 16(Issue 12) pp:7317-7324
Publication Date(Web):November 11, 2016
DOI:10.1021/acs.nanolett.6b02004
The heteroepitaxial growth of crystal silicon thin films on sapphire, usually referred to as SoS, has been a key technology for high-speed mixed-signal integrated circuits and processors. Here, we report a novel nanoscale SoS heteroepitaxial growth that resembles the in-plane writing of self-aligned silicon nanowires (SiNWs) on R-plane sapphire. During a low-temperature growth at <350 °C, compared to that required for conventional SoS fabrication at >900 °C, the bottom heterointerface cultivates crystalline Si pyramid seeds within the catalyst droplet, while the vertical SiNW/catalyst interface subsequently threads the seeds into continuous nanowires, producing self-oriented in-plane SiNWs that follow a set of crystallographic directions of the sapphire substrate. Despite the low-temperature fabrication process, the field effect transistors built on the SoS-SiNWs demonstrate a high on/off ratio of >5 × 104 and a peak hole mobility of >50 cm2/V·s. These results indicate the novel potential of deploying in-plane SoS nanowire channels in places that require high-performance nanoelectronics and optoelectronics with a drastically reduced thermal budget and a simplified manufacturing procedure.Keywords: heteroepitaxy; In-plane Si nanowires; self-alignment; silicon on sapphire;
Co-reporter:Hucheng Song;Hong Xiang Wang;Zixia Lin;Xiaofan Jiang;Linwei Yu;Zhongwei Yu;Xiaowei Zhang;Yijie Liu;Ping He;Lijia Pan;Yi Shi;Haoshen Zhou;Kunji Chen
Advanced Functional Materials 2016 Volume 26( Issue 4) pp:524-531
Publication Date(Web):
DOI:10.1002/adfm.201504014
Seeking high-capacity, high-rate, and durable anode materials for lithium-ion batteries (LIBs) has been a crucial aspect to promote the use of electric vehicles and other portable electronics. Here, a novel alloy-forming approach to convert amorphous Si (a-Si)-coated copper oxide (CuO) core–shell nanowires (NWs) into hollow and highly interconnected Si–Cu alloy (mixture) nanotubes is reported. Upon a simple H2 annealing, the CuO cores are reduced and diffused out to alloy with the a-Si shell, producing highly interconnected hollow Si–Cu alloy nanotubes, which can serve as high-capacity and self-conductive anode structures with robust mechanical support. A high specific capacity of 1010 mAh g−1 (or 780 mAh g−1) has been achieved after 1000 cycles at 3.4 A g−1 (or 20 A g−1), with a capacity retention rate of ≈84% (≈88%), without the use of any binder or conductive agent. Remarkably, they can survive an extremely fast charging rate at 70 A g−1 for 35 runs (corresponding to one full cycle in 30 s) and recover 88% capacity. This novel alloy-nanotube structure could represent an ideal candidate to fulfill the true potential of Si-loaded LIB applications.
Co-reporter:Hucheng Song, Hong Xiang Wang, Zixia Lin, Linwei YU, Xiaofan Jiang, Zhongwei Yu, Jun XU, Lijia Pan, Mingbo Zheng, Yi Shi, Kunji Chen
Nano Energy 2016 Volume 19() pp:511-521
Publication Date(Web):January 2016
DOI:10.1016/j.nanoen.2015.10.031
•A hybrid hierarchical structure of Si nanowires (NWs) grafted upon SnO2 NWs trunks.•Boosting both the specific capacity (3400 mAh/g) and the stability of Si-loaded LIBs.•With a high mass-load ~1.5 mg/cm2 and record-high areal capacity of 1.8 mAh/cm2.Hierarchical structures, with a high mass-loading of nanostructured lithium (Li) storage medium grafted upon large trunk framework, represent a novel approach towards high capacity and stable Li-ion batteries. We here report a new hierarchical structure of crystalline Si nanowires (c-Si NWs) grafted upon ultra-long tin dioxide (SnO2) NW trunks, where the latter frame up a large, conductive and stable architecture (i) to achieve a high mass-loading of c-Si NWs for Li-ion storage and (ii) to guarantee a good electric contact and fast charging process. The Si NWs branches are produced via a low-temperature vapor-liquid-solid (VLS) growth catalyzed by Sn droplets produced during a simple H2 plasma treatment upon the SnO2 trunks. Compared to other Si or SnO2 NW-based anodes structures, the c-Si/SnO2 NWs hierarchical structure demonstrates an outstanding performance with a high mass-load (~1.5 mg/cm2) and a high areal capacity (~1.8 mAh/cm2) after 100 cycles, without the use of any additional conductive polymer binder, highlighting the unique synergistic benefit of this hierarchical structure in boosting simultaneously the capacity and stability of Si-loaded Li-ion batteries.
Co-reporter:Yunqing Cao, Jun Xu, Zhaoyun Ge, Yingying Zhai, Wei Li, Xiaofan Jiang and Kunji Chen
Journal of Materials Chemistry A 2015 vol. 3(Issue 46) pp:12061-12067
Publication Date(Web):28 Oct 2015
DOI:10.1039/C5TC02585K
In order to circumvent the narrow spectral response of Si quantum dots (Si QDs)-based solar cells, a novel hetero-junction cell structure containing graded-sized QDs-based multilayers was proposed. The size of Si QDs varies from 8 nm to 2 nm which corresponds with the bandgap from 1.2 eV to 2.1 eV. The graded-sized Si QDs-based hetero-junction cell exhibits an enhanced spectral response in a wavelength range from 400 nm to 1200 nm, which is obviously improved compared with that of conventional Si QDs-based cells. Furthermore, by combining the graded-sized Si QDs multilayers with Si nanowire arrays, a Si QDs/Si NWs hetero-junction solar cell was fabricated and the corresponding power conversion efficiency can be as high as 12.80%, due to the significant spectral loss suppression and optical absorption enhancement by forming nano-patterned light trapping structures.
Co-reporter:Xiaowei Zhang, Shaobing Lin, Tao Lin, Pei Zhang, Jun Xu, Ling Xu and Kunji Chen
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 18) pp:11974-11980
Publication Date(Web):16 Feb 2015
DOI:10.1039/C5CP00246J
Er3+ ions and SnO2 nanocrystals co-doped silica thin films are prepared by an improved sol–gel spin-coating method. With increase in annealing temperature, the related 1.54 μm characteristic emission intensity from Er3+ ions is obviously enhanced by more than two orders of magnitude via SnO2 nanocrystals size control to boost the sensitization efficiency. Quantitative studies of steady-state spectroscopic data and fluorescence decay curves demonstrate that the related sensitization efficiency via size-tunable nanocrystals is increased from 0.14% to 1.3%. This improved sensitization efficiency is achieved by doping some of the Er3+ ions into the SnO2 inner sites at a high annealing temperature, as revealed by high-resolution TEM, X-ray diffraction patterns and elemental mapping technique. Different sensitization mechanisms are also discussed separately according to the selective photoluminescence excitation measurements. All these results have not only explained the greatly improved sensitization efficiency resulting from SnO2 nanocrystals but also indicated that the development of Er3+ ions and SnO2 nanocrystals co-doped silica thin films could result in promising high-performance near-infrared luminous materials using broadband UV pumping.
Co-reporter:Peng Lu, Jun Xu, Yunqing Cao, Jingwei Lai, Ling Xu, Kunji Chen
Applied Surface Science 2015 Volume 334() pp:123-128
Publication Date(Web):15 April 2015
DOI:10.1016/j.apsusc.2014.08.129
Highlights
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220 nm and 300 nm periodic Si nanostructures were fabricated by using nano-sphere lithography technique.
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A good antireflection character was identified and the weighted mean reflection is 2.96% for 300 nm periodic nano-patterned structures with low aspect ratio.
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Nano-patterned hetero-junction solar cells were prepared and the improved device performance was demonstrated to be directly correlated with light trapping effect.
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The short circuit current density can be increased to 34.5 mA/cm2 which is significantly enhanced compared with the value of flat cell.
Co-reporter:Pei Zhang, Xiaowei Zhang, Peng Lu, Jun Xu, Xin Xu, Wei Li, Kunji Chen
Applied Surface Science 2014 Volume 292() pp:262-266
Publication Date(Web):15 February 2014
DOI:10.1016/j.apsusc.2013.11.128
Highlights
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Periodic nc-Si/SiO2 multilayers with dot size of 2.5 nm were prepared and room temperature luminescence was achieved.
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Both nonlinear optical absorption and nonlinear optical refraction with strong nonlinear response were observed under ps and fs laser excitation.
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The model based on the interface state-assisted process was proposed to explain the observed linear and nonlinear optical properties.
Co-reporter:Xiaowei Zhang;Pei Zhang;Shaobing Lin;Tao Lin
Science Bulletin 2014 Volume 59( Issue 12) pp:1285-1290
Publication Date(Web):2014 April
DOI:10.1007/s11434-014-0168-y
Eu3+ ions embedded in silica thin films co-doped with SnO2 nanocrystals were fabricated by sol–gel and spin-coating methods. SnO2 nanocrystals with controllable sizes were synthesized through precisely controlling the Sn concentrations. The influences of doping and annealing conditions on the photoluminescence intensity from SnO2 nanocrystals are systematically investigated. The effective energy transfer from the defect states of SnO2 nanocrystals to nearby Eu3+ ions has revealed by the selective photoluminescence excitation spectra. The efficiency of the Förster resonance energy transfer is evaluated by the time-resolved photoluminescence measurements, which is about 29.1 % based on the lifetime tests of the SnO2 emission.
Co-reporter:Jie Xu, Jun Xu, Pengzhan Zhang, Wei Li and Kunji Chen
Nanoscale 2013 vol. 5(Issue 20) pp:9971-9977
Publication Date(Web):08 Aug 2013
DOI:10.1039/C3NR03306F
Si nanocrystals are formed by using KrF pulsed laser crystallization of an amorphous SiC/ultrathin amorphous Si/amorphous SiC sandwiched structure. Electrons and holes are injected into Si nanocrystals via a biased conductive AFM tip and the carrier decay and transportation behaviours at the nanoscale are studied by joint characterization techniques of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM). Quantification of the surface charge density is realized by solving the Poisson equation based on KPFM measurements. Besides, the asymmetric barrier height for electrons and holes is considered to play a dominant role in controlling the charge retention and transportation characteristics. The methodology developed in this work is promising for studying the charge injection and transportation process in other materials and structures at the nanoscale.
Co-reporter:Yunjun Rui, Shuxin Li, Yunqing Cao, Jun Xu, Wei Li, Kunji Chen
Applied Surface Science 2013 Volume 269() pp:37-40
Publication Date(Web):15 March 2013
DOI:10.1016/j.apsusc.2012.09.118
Abstract
Si quantum dots (QDs)/SiC multilayered structures were prepared by thermal annealing the hydrogenated amorphous silicon (a-Si:H)/hydrogenated amorphous silicon carbide (a-SiC:H) multilayers. The microstructures of annealed samples were investigated by Raman scattering, cross-sectional transmission electron microscopy, and Fourier transform infrared spectroscopy. The size of formed Si QDs can be controlled by the a-Si:H layer thickness and annealing conditions. Room temperature electroluminescence (EL) was observed and the EL peak energy was shifted with the size of the Si QDs formed in the annealed multilayers, which can be attributed to quantum confinement effect in Si QDs.
Co-reporter:Cong Li, Jun Xu, Ling Xu, Wei Li, Xiaofan Jiang, Shenghua Sun, Kunji Chen
Applied Surface Science 2013 Volume 269() pp:129-133
Publication Date(Web):15 March 2013
DOI:10.1016/j.apsusc.2012.10.181
Abstract
Nanocrystalline Ge (nc-Ge)/SiNx multilayers and sandwiched structures were fabricated by thermally annealing amorphous Ge/SiNx layered films at 600 °C. The evolution of microstructure before and after annealing was studied by various characterization techniques, which reveals the formation of nc-Ge after annealing. The tunable optical absorption and band gap were observed by changing the grain size of nc-Ge. The study on carrier transport behavior of nc-Ge/SiNx MLs indicated that the transport process was dominated by space-charge limited current mechanism. Furthermore, the charging storage effect in SiNx/nc-Ge/SiNx floating gate structures was demonstrated due to both the electron and hole injection processes.
Co-reporter:Shenghua Sun;Peng Lu;Ling Xu;Kunji Chen;Qimin Wang
Nano-Micro Letters 2013 Volume 5( Issue 1) pp:18-25
Publication Date(Web):2013 March
DOI:10.1007/BF03353727
Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy. A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio (<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.
Co-reporter:Yun-Qing Cao;Xin Xu;Shu-Xin Li;Wei Li
Frontiers of Optoelectronics 2013 Volume 6( Issue 2) pp:228-233
Publication Date(Web):2013 June
DOI:10.1007/s12200-013-0324-z
Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC stacked structures prepared in plasma enhanced chemical vapor deposition (PECVD) system. The microstructures were examined by transmission electron microscopy (TEM) and Raman spectroscopy, and results demonstrate the formation of Si QDs. Moreover, p-i-n devices containing Si QDs/SiC multilayers were fabricated, and their photovoltaic property was investigated. It was found that these devices show the good spectral response in a wide wavelength range (400–1200 nm). And it was also observed that by reducing the thickness of SiC layer from 4 to 2 nm, the external quantum efficiency was obviously enhanced and the short circuit current density (Jsc) was increased from 17.5 to 28.3 mA/cm2, indicating the collection efficiency of photo-generated carriers was improved due to the reduced SiC barriers.
Co-reporter:Yunjun Rui, Shuxin Li, Jun Xu, Yunqing Cao, Wei Li, Kunji Chen
Journal of Non-Crystalline Solids 2012 Volume 358(Issue 17) pp:2114-2117
Publication Date(Web):1 September 2012
DOI:10.1016/j.jnoncrysol.2012.01.054
Si quantum dots (Si QDs) films were prepared by annealing amorphous SiC single layer and amorphous Si/SiC multilayers fabricated in plasma enhanced chemical vapor deposition system. The microstructures were characterized by Raman spectroscopy as well as Fourier transforms infrared spectroscopy for both samples. It was found that Si QDs with average size of 2.7 nm were formed after annealing and the electroluminescence (EL) band centered at 650 nm can be observed at room temperature. The EL intensity from the Si/SiC multilayers was obviously improved by one order of magnitude and the corresponding EL band width was reduced compared with that from SiC single layer film. The improved electroluminescence behavior can be attributed to the formation of the denser Si QDs, good size distribution and the strong confinement effect of carriers in multilayerd structures.Highlights► Si QDs can be formed in a-SiC single layer and a-Si/SiC multilayers (MLs). ► Si QDs has higher density and better size distribution in Si/SiC MLs. ► EL (intensity and FWHM) was improved in the Si/SiC MLs. ► EL is originated from radiative recombination of e-h pairs in Si QDs.
Co-reporter:Jun Xu, Weiwei Mu, Zhengyue Xia, Hongchen Sun, Deyuan Wei, Wei Li, Zhongyuan Ma, Kunji Chen
Journal of Non-Crystalline Solids 2012 Volume 358(Issue 17) pp:2141-2144
Publication Date(Web):1 September 2012
DOI:10.1016/j.jnoncrysol.2011.12.009
Si quantum dots/SiO2 multilayers were prepared by annealing a-Si:H/SiO2 stacked structures at 1100 °C . Photo- and electro-luminescence band around 750 nm can be observed from Si QDs/SiO2 multilayers due to the recombination of electron-hole pairs in Si QDs/SiO2 interfaces. The electro-luminescence intensity was obviously enhanced after post hydrogen annealing at 400 °C. Electron spin resonance measurements were used to characterize the change of the defect states after hydrogen annealing. It is found that there exists a-centers (g value = 2.006), which is related to the Si dangling bonds in Si QDs in our samples. Hydrogen annealing can significantly reduce non-luminescent a-centers and enhance the electro-luminescence intensity consequently.Highlights► Si QDs/SiO2 multilayers were prepared by annealing a-Si:H/SiO2 stacked structures. ► Room temperature electroluminescence can be observed from Si QDs-based multilayers. ► EL intensity is significantly enhanced by hydrogen annealing at 400 °C. ► ESR demonstrated that hydrogen annealing can passivate defect states in Si QDs.
Co-reporter:Tao Lin, Xiao-wei Zhang, Yun-ji Wang, Jun Xu, Neng Wan, Jian-feng Liu, Ling Xu, Kun-ji Chen
Thin Solid Films 2012 Volume 520(Issue 17) pp:5815-5819
Publication Date(Web):30 June 2012
DOI:10.1016/j.tsf.2012.04.058
SiO2 thin films co-doped with ZnO nanoparticles and Eu3 + ions were prepared by sol–gel method. The formation of nano-sized ZnO particles was confirmed by X-ray diffraction patterns and transmission electron microscopy. The characteristic emission bands from Eu3 + ions can be observed at room temperature and the luminescence intensity is increased obviously by introducing ZnO nanoparticles into Eu3 +-doped silica films. The integrated luminescence intensity is influenced by the concentration and size of ZnO particles, suggesting effective energy transfer from nano-sized ZnO to Eu3 + ions. It is argued that the efficient luminescence enhancement occurs under the suitable Zn2 + amount and annealing temperature.Highlights► In-situ formation of nano-sized ZnO particles in amorphous SiO2. ► Photoluminescence enhancements of Eu3 + ions by introduction of ZnO nanoparticles. ► The analysis of energy transfer process from ZnO nanoparticles to Eu3 + ions.
Co-reporter:Shuxin Li;Yunjun Rui;Yunqing Cao;Kunji Chen
Frontiers of Optoelectronics 2012 Volume 5( Issue 1) pp:107-111
Publication Date(Web):2012 March
DOI:10.1007/s12200-012-0196-7
A series of Si-rich amorphous silicon carbide (a-SiC:H) thin films were deposited in conventional plasma enhanced chemical vapor deposition system with various gas ratio R = [CH4]/[SiH4]. The microstructural, optical and electronic properties of as-deposited films were investigated in this study. It was found that optical band gap was linearly proportional to carbon content in the films and it could be controlled in a range of 1.8–2.4 eV by changing the gas ratio, R. Both dark and photo conductivities in room temperature were decreased with the increasing of carbon content in the films, and the photosensitivity reached as high as 104 for the film with the optical band gap of 1.96 eV. The as-deposited samples were subsequently annealed at the temperatures of 900°C and 1000°C. The formation of nanocrystalline silicon (nc-Si) dots in amorphous silicon carbide (a-SiC) host matrix was shown. The dark conductivity was enhanced by five orders of magnitude after annealing compared with that of as-deposited films. The result of temperature-dependent conductivity suggested that the property of carrier transport was dominated by conduction process between the extended states. Furthermore, room temperature electroluminescence (EL) was achieved from nc-Si/SiC system and the possible mechanism of radiative recombination mechanism was discussed.
Co-reporter:Chao Song, Yunjun Rui, Quanbiao Wang, Jun Xu, Wei Li, Kunji Chen, Yuhua Zuo, Qiming Wang
Journal of Alloys and Compounds 2011 Volume 509(Issue 9) pp:3963-3966
Publication Date(Web):3 March 2011
DOI:10.1016/j.jallcom.2010.12.191
Si-rich hydrogenated amorphous silicon carbide thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited films were subsequently annealed at 900 °C and 1000 °C to form Si nanocrystals embedded in amorphous SiC matrix. Raman spectra demonstrate the formation of Si nanocrystals with size around 7–9 nm. For the sample annealed at 1000 °C, the crystallinity can be reached to 70%. As increasing the annealing temperature, the dark conductivity is increased accompanying with the increase of crystallinity of the film. The dark conductivity reaches to 1.2 × 10−6 S cm−1 for the sample annealed at 1000 °C, which is 4 orders of magnitude higher than that of as-deposited film. It is found that the carrier transport process is dominated by the thermally activated transport process according to the temperature-dependent conductivity results.Research highlights▶ Amorphous silicon carbide thin films were annealed at 900 °C and 1000 °C to form Si nanocrystals embedded in amorphous SiC matrix. The average size of Si nanocrystals is around 7–9 nm. For the sample annealed at 1000 °C, the crystallinity can be reached to 70%. ▶ As increasing the annealing temperature, the dark conductivity is increased accompanying with the increase of crystallinity of the film. The dark conductivity reaches to 1.2 × 10−6 S cm−1 for the sample annealed at 1000 °C, which is 4 orders of magnitude higher than that of as-deposited film. ▶ The possible transport mechanism was proposed and discussed. The temperature-dependent conductivity results reveal that the carrier transport process is dominated by the thermally activated transport process.
Co-reporter:W. Xu, H.C. Sun, J. Xu, W. Li, W.W. Mu, Y. Liu, M.Y. Yan, X.F. Huang, K.J. Chen
Applied Surface Science 2011 Volume 258(Issue 1) pp:346-349
Publication Date(Web):15 October 2011
DOI:10.1016/j.apsusc.2011.08.062
Abstract
We report the fabrication of Si quantum dots (QDs)/SiO2 multilayers by using KrF excimer laser (248 nm) crystallization of amorphous Si/SiO2 multilayered structures on ITO coated glass substrates. Raman spectra and transmission electron microscopy demonstrate the formation of Si QDs and the size can be controlled as small as 1.8 nm. After laser crystallization, Al electrode is evaporated to obtain light emitting devices and the room temperature electroluminescence (EL) can be detected with applying the DC voltage above 8 V on the top gate electrode. The luminescent intensity increases with increasing the applied voltage and the micro-watt light output is achieved. The EL behaviors for samples with different Si dot sizes are studied and it is found that the corresponding external quantum efficiency is significantly enhanced in sample with ultra-small sized Si QDs.
Co-reporter:Chao Song, Jun Xu, Quanbiao Wang, Guowei Zha, Wei Li, Kunji Chen
Solid State Communications 2011 Volume 151(Issue 9) pp:697-700
Publication Date(Web):May 2011
DOI:10.1016/j.ssc.2011.02.018
Phosphorus- and boron-doped hydrogenated amorphous silicon thin films were prepared by the plasma-enhanced chemical vapor deposition method. As-deposited samples were thermally annealed at various temperatures to get nanocrystalline Si with sizes around 10 nm. X-ray photoelectron spectroscopy measurements demonstrated the presence of boron and phosphorus in the doped films. It is found that the nanocrystallization occurs at around 600 °C for the B-doped films, while it is around 700–800 °C for the P-doped samples. For the P-doped samples, the dark conductivity decreases at first and then increases with the annealing temperature. While for the B-doped samples, the dark conductivity monotonously increases with increasing annealing temperature. As a result, the carrier transport properties of both P- and B-doped nanocrystalline Si films are dominated by the gradual activation of dopants in the films. The conductivity reaches 22.4 and 193 S cm−1 for P- and B-doped sample after 1000 °C annealing.Research highlights► The effect of the annealing temperature is investigated. ► The activation effect of the dopant can be promoted in conjunction with the formation of nc-Si. ► A possible transport mechanism is proposed and discussed.
Co-reporter:Neng Wan, Jun Xu, Guran Chen, Xinhui Gan, Sihua Guo, Ling Xu, Kunji Chen
Acta Materialia 2010 Volume 58(Issue 8) pp:3068-3072
Publication Date(Web):May 2010
DOI:10.1016/j.actamat.2010.01.041
Abstract
Small-sized indium tin oxide (ITO) nanowires were fabricated using the electron beam evaporation (EBE) technique at low temperature (∼150 °C) without adding any catalyst. The ITO nanowires have a typical diameter of around 10 nm and a length of more than 100 nm, with body-centered cubic crystal structures that grow along the 〈1 0 0〉 directions, as revealed by transmission electron microscopy. The growth mechanism of the branched ITO nanowires was found to be a vapor–solid process. The nanowire films show a broadband anti-reflection property due to the graded refraction index from the film surface to the substrate. Enhanced field emission properties with a low turn-on electric field and a high field enhancement factor were also observed in the ITO nanowires.
Co-reporter:Chao Song, Jun Xu, Guran Chen, Hongcheng Sun, Yu Liu, Wei Li, Ling Xu, Zhongyuan Ma, Kunji Chen
Applied Surface Science 2010 Volume 257(Issue 4) pp:1337-1341
Publication Date(Web):1 December 2010
DOI:10.1016/j.apsusc.2010.08.065
Abstract
Intrinsic, P- and B-doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The microstructures, optical and electronic properties have been evaluated for the undoped and doped nanocrystalline films. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron and phosphorous in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the activation of dopant by annealing increased the room temperature dark conductivity from 3.4 × 10−4 S cm−1 to 5.3 S cm−1 for the P-doped films and from 1.28 × 10−3 S cm−1 to 130 S cm−1 for the B-doped films. Meanwhile, the corresponding value of conductivity activation energies was decreased from 0.29 eV to 0.03 eV for the P-doped films and from 0.3 eV to 5.6 × 10−5 eV for the B-doped films, which indicated the doped nc-Si films with high conductivity can be achieved with the present approach.
Co-reporter:Jun Xu, Guran Chen, Chao Song, Kunji Chen, Xinfan Huang, Zhongyuan Ma
Applied Surface Science 2010 Volume 256(Issue 18) pp:5691-5694
Publication Date(Web):1 July 2010
DOI:10.1016/j.apsusc.2010.03.016
Abstract
Laser induced crystallization of ultrathin hydrogenated amorphous Si films or amorphous Si-based multilayered structures were used to get high density Si nanodots. The present technique can get size controllable Si nanodots embedded in various dielectric materials with uniform distribution which was revealed by cross-section transmission electron microscopy. Room temperature photoluminescence and electroluminescence were achieved with the emission wavelength in a visible light region both from a-SiN/Si nanodots/a-SiN sandwiched and Si nanodots/SiO2 multilayered structures. The luminescence was associated with the radiative recombination of generated electron–hole pairs in Si nanodots or the luminescent surface states. The electroluminescence intensity is increased with increasing the injection current implying the bipolar carrier injection plays an important role in enhancing the luminescence efficiency. The formed Si nanodots by the present approach can be applied for many kinds of devices such as high efficient light emitting diodes and solar cells.
Co-reporter:Neng Wan, Tao Wang, Hongcheng Sun, Guran Chen, Lei Geng, Xinhui Gan, Sihua Guo, Jun Xu, Ling Xu, Kunji Chen
Journal of Non-Crystalline Solids 2010 Volume 356(18–19) pp:911-916
Publication Date(Web):15 April 2010
DOI:10.1016/j.jnoncrysol.2009.12.026
Tin doped indium oxide thin films were deposited by electron beam evaporation (EBE) method. The influences of deposition atmosphere, film thickness and post-annealing temperature on the optical and electrical properties are studied. It is found that depositing films in oxygen atmosphere is helpful for improving the electrical and optical performance due to the improvement of the film microstructure. The sheet resistance is increased obviously in ITO films with reducing the film thickness, which is caused by the enhanced surface scattering towards the carriers. The obtained ITO thin films deposited under optimized conditions have good electrical and optical properties with typical resistivity of 4.5 × 10−4 Ω cm and the optical transmittance of about 85% (at 550 nm). Furthermore, the EBE deposited ITO thin film can be applied as the top electrode in the Si-based electro-luminescence devices and a strong electro-luminescence (EL) is observed.
Co-reporter:J. Xu, K. Makihara, H. Deki, S. Miyzazki
Solid State Communications 2009 Volume 149(19–20) pp:739-742
Publication Date(Web):May 2009
DOI:10.1016/j.ssc.2009.03.013
Si quantum dots/SiO2 multilayers with ultrathin oxide layers (2.4 nm) were fabricated on a p-type Si substrate in order to enhance the hole injection. Besides the luminescence band at 900 nm which was also shown in photoluminescence spectra, another strong luminescence band near the infrared region (1200 nm) can be observed in electroluminescence spectra. It can be assigned to the band-edge emission from the quasi 2-dimensional potential well in the Si substrate. Moreover, it is interesting to find the reduction of photoluminescence intensity under biased conditions which can be attributed to the occurrence of non-radiative Auger recombination process in charged Si quantum dots.
Co-reporter:Deyuan Chen, Jun Xu, Bo Qian, San Chen, Jiaxin Mei, Wei Li, Ling Xu, Kunji Chen
Materials Chemistry and Physics 2008 Volume 111(2–3) pp:279-282
Publication Date(Web):15 October 2008
DOI:10.1016/j.matchemphys.2008.04.008
All solid-state optical microcavities based on amorphous silicon-carbide films were designed and prepared in conventional plasma chemical vapor deposition system. The resonant cavity mode was clearly observed in the transmission spectrum, which is in well agreement with the pre-designed value. Room temperature photoluminescence spectra were studied which contain both the enhanced emission band at resonant mode and the stop-band edge emission bands. The luminescence intensity is significantly enhanced and the bandwidth is obviously narrowed at the resonant wavelength due to the Si-based optical cavity structures. The modulation effect of cavity on the transmission and emission behaviors was investigated by angle-dependent transmission, photoluminescence spectra together with photoluminescence excitation spectra.
Co-reporter:Jun Xu, Jiang Zhou, Yao Yao, Zhanhong Cen, Fenqi Song, Ling Xu, Jianguo Wan, Kunji Chen
Solid State Communications 2008 Volume 145(9–10) pp:443-446
Publication Date(Web):March 2008
DOI:10.1016/j.ssc.2007.12.019
Co-reporter:Yunjun Rui, Deyuan Chen, Jun Xu, Wei Li, Zhanhong Cen, Xinfan Huang, Kunji Chen
Applied Surface Science 2007 Volume 253(Issue 21) pp:8647-8651
Publication Date(Web):31 August 2007
DOI:10.1016/j.apsusc.2007.04.058
Abstract
Effects of post-hydrogen plasma annealing (HPA) on a-Si:H/SiO2 and nc-Si/SiO2 multilayers have been investigated and compared. It is found that photoluminescence (PL) from hydrogen-passivated samples was improved due to the reduction of non-radiative recombination defects. Some interesting difference is that during HPA, atomic hydrogen can directly passivate defects of a-Si:H/SiO2, which results in the reappearance of luminescence band at 760 nm, while for nc-Si/SiO2, hydrogen passivation requires additional thermal annealing after nc-Si/SiO2 multilayer was treated by HPA. It is indicated that higher atomic mobility is needed to passivate defects at nc-Si/SiO2 interface compared with a-Si:H/SiO2 interface.
Co-reporter:T. Wang, D.Y. Wei, H.C. Sun, Y. Liu, D.Y. Chen, G.R. Chen, J. Xu, W. Li, Z.Y. Ma, L. Xu, K.J. Chen
Physica E: Low-dimensional Systems and Nanostructures (May 2009) Volume 41(Issue 6) pp:923-926
Publication Date(Web):1 May 2009
DOI:10.1016/j.physe.2008.08.001
Amorphous-Si:H/SiO2 multilayers were fabricated on various substrates by alternatively changing the ultra-thin amorphous Si films deposition and in situ plasma oxidation processes. Uniform silicon nanodots with controllable size were formed by combining the rapid thermal annealing and furnace annealing techniques as revealed by cross-sectional transmission electron microscopy. Light-emitting diodes based on Al/(nc-Si/SiO2) multilayers/Si substrate/Al structures were fabricated and electrically driven luminescence was demonstrated at room temperature. It was found that the substrate had a significant impact on the carrier injection efficiency and the luminescence intensity. The turn-on voltages of the device on p+-Si and p-Si substrate were 2.2 and 8 V, respectively. Meanwhile, electroluminescence intensity of the device on p+-Si substrate was five times higher than that on p-Si substrate under the same power supply, which means the heavily doped substrate is helpful for enhancing the carrier injection efficiency.
Co-reporter:S.X. Li, Y.Q. Cao, J. Xu, Y.J. Rui, W. Li, K.J. Chen
Applied Surface Science (1 April 2013) Volume 270() pp:
Publication Date(Web):1 April 2013
DOI:10.1016/j.apsusc.2012.12.176
Hydrogenated amorphous silicon carbide thin films with high photo-sensitivity were fabricated by using layer-by-layer hydrogen annealing technique in conventional plasma enhanced chemical vapor deposition system. It was found that the photo-conductivity is increased from 1.9 × 10−7 to 1.5 × 10−6 S/cm after layer-by-layer hydrogen annealing. The photo-sensitivity can reach as high as 106 for sample with optical band gap of 2.11 eV. The influence of the hydrogen annealing time on film quality and optical properties were investigated. It was demonstrated that the layer-by-layer hydrogen annealing technique can improve the film quality, which can be attributed to both the hydrogen chemical annealing and hydrogen passivation effect.Highlights► a-SiC:H films were prepared by layer-by-layer hydrogen plasma annealing technique. ► The electrical and optical properties of prepared films were studied. ► Photo-conductivity was improved after hydrogen plasma annealing. ► High photo-sensitivity (∼106) was achieved for 10 s layer-by-layer annealed film.
Co-reporter:Yunqing Cao, Jun Xu, Zhaoyun Ge, Yingying Zhai, Wei Li, Xiaofan Jiang and Kunji Chen
Journal of Materials Chemistry A 2015 - vol. 3(Issue 46) pp:NaN12067-12067
Publication Date(Web):2015/10/28
DOI:10.1039/C5TC02585K
In order to circumvent the narrow spectral response of Si quantum dots (Si QDs)-based solar cells, a novel hetero-junction cell structure containing graded-sized QDs-based multilayers was proposed. The size of Si QDs varies from 8 nm to 2 nm which corresponds with the bandgap from 1.2 eV to 2.1 eV. The graded-sized Si QDs-based hetero-junction cell exhibits an enhanced spectral response in a wavelength range from 400 nm to 1200 nm, which is obviously improved compared with that of conventional Si QDs-based cells. Furthermore, by combining the graded-sized Si QDs multilayers with Si nanowire arrays, a Si QDs/Si NWs hetero-junction solar cell was fabricated and the corresponding power conversion efficiency can be as high as 12.80%, due to the significant spectral loss suppression and optical absorption enhancement by forming nano-patterned light trapping structures.
Co-reporter:Xiaowei Zhang, Shaobing Lin, Tao Lin, Pei Zhang, Jun Xu, Ling Xu and Kunji Chen
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 18) pp:NaN11980-11980
Publication Date(Web):2015/02/16
DOI:10.1039/C5CP00246J
Er3+ ions and SnO2 nanocrystals co-doped silica thin films are prepared by an improved sol–gel spin-coating method. With increase in annealing temperature, the related 1.54 μm characteristic emission intensity from Er3+ ions is obviously enhanced by more than two orders of magnitude via SnO2 nanocrystals size control to boost the sensitization efficiency. Quantitative studies of steady-state spectroscopic data and fluorescence decay curves demonstrate that the related sensitization efficiency via size-tunable nanocrystals is increased from 0.14% to 1.3%. This improved sensitization efficiency is achieved by doping some of the Er3+ ions into the SnO2 inner sites at a high annealing temperature, as revealed by high-resolution TEM, X-ray diffraction patterns and elemental mapping technique. Different sensitization mechanisms are also discussed separately according to the selective photoluminescence excitation measurements. All these results have not only explained the greatly improved sensitization efficiency resulting from SnO2 nanocrystals but also indicated that the development of Er3+ ions and SnO2 nanocrystals co-doped silica thin films could result in promising high-performance near-infrared luminous materials using broadband UV pumping.
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