Low-temperature fabrication of nanocrystalline silicon thin films on mechanically flexible substrates by vacuum arc disc
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niel H.C. Chua Department of Materials Science & Engineering, National University of Singapore, Singapore 117574 (Received 5 October 2010; accepted 8 February 2011)
Nanocrystalline silicon thin films were fabricated using a vacuum arc discharge technique. These thin films can be deposited on plastic substrates effectively when cooled by a cryogenic substrate holder. We used single crystal silicon wafers as both the electrodes to ignite the vacuum arc and the silicon ion source to deposit thin films. This resulted in nanocrystalline silicon clusters embedded in the amorphous silicon matrix. This thin film has highly crystalline volume (87%), which enhanced the absorption in wide range of wavelengths. Without ion implantation, the in situ doping of p- or n-type thin films can also be achieved. This thin film deposition process has its potential for fabricating thin film transistors and photovoltaic cells on plastic substrates at fairly low production costs.
I. INTRODUCTION
Amorphous silicon (a-Si) thin film is an important semiconductor that has been used in modern microelectronic systems, for example, large glass plates with p-i-n structure for assembly into low-cost solar cells had deposition of a-Si1 and radio frequency identification (RFID) tags contains a-Si thin film transistor (TFTs) as the major active material.2 These thin films were mainly fabricated using radio-frequency glow discharge reactors, the latter more commonly known as plasma-enhanced chemical vapor deposition (PECVD) systems, where silane was dissociated by the plasma reactions. A largesized air-shower head allows uniform deposition silicon films of sizes above 1 m2 on glass plates. This explains why these amorphous thin films are the fundamental material for constructing TFT in large-sized liquid crystal displays (LCDs). Owing to the disordered nature of this amorphous semiconductor, low carrier mobility limits the performance of switching time in TFTs.3 The consequence is that active-matrix LCDs operate at relatively lower speeds compared to the single crystal silicon–based transistors. In addition, there are disadvantages in using a-Si in photovoltaic applications. For example, hydrogenated amorphous silicon (a-Si:H) solar cells are affected by the formation of metastable defects, which provide recombination of extra electrons and holes when photon generation assesses carriers. Hence, it reduced 20–30% of the cell efficiency.4 As such, the improvement in the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.48 1076
J. Mater. Res., Vol. 26, No. 9, May 14, 2011
http://journals.cambridge.org
Downloaded: 13 Mar 2015
material properties is an important issue for the continual commercialization of electronic products. One key point when comparing both research results and industrial production is the concern in the process temperature, which is related to the production cost. The conventional plasma process requires a temperature of 350 °C or above to achieve the uniform deposition of a-Si films at a deposition r
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