The hot wire (HW) cell method has been newly developed and successfully applied to grow polycrystalline silicon films at low temperatures with a relatively high growth rate of 0.9–1.1 nm/s. In the HW cell method, mono silane (SiH4) is decomposed by reacting with a heated tungsten wire placed near the substrate. It is found that polycrystalline silicon films can be obtained at substrate temperatures of 175–400°C without hydrogen dilution when the deposition pressure is 0.1 Torr.
Hot wire (HW) cell method has been newly developed and successfully applied to grow polycrystalline silicon films at a low temperature with a relatively high growth rate. In the HWcell method, silane is decomposed by reaction with a heated tungsten wire placed near the substrate. It is found that polycrystalline silicon films can be obtained at substrate temperatures of 175-400°C without hydrogen dilution. The film crystallinity is changed from polycrystalline to amorphous with decreasing the total pressure. The X-ray analysis clearly showed that the films grown at the filament temperature of 1700°C have a very strong (220) preferential orientation. The films consist of large grains as well as small grains, and it was found from cross-sectional SEM that the films have columnar structure. These results suggested that the HW-cell method would be a promising candidate to grow device-grade polycrystalline silicon films for photovoltaic application.
One-dimensional metal droplet arrays of Ga and Al, the mean size of which was smaller than 8 nm, were formed along step edges on the surface of epitaxial CaF2 film in a self-assembling manner. The two-step method by which Al and Ga were sequentially deposited to grow Ga/Al double layer droplets was examined, and it was shown to be suitable to reduce gap spacing between neighboring droplets. A multitunnelling junction (MTJ) of Ga/Al droplets was formed by a two-step method and a MTJ diode was fabricated by a conventional lift-off process. Current–voltage characteristic of the device showed a Coulomb staircase at 25 K and room temperature.
Spontaneous loss of charge by charged black holes by means of pair-creation of charged Dirac particles is considered. We provide three examples of exact calculations for the spontaneous discharge process for 4D charged black holes by considering the process on three special non-rotating de Sitter black hole backgrounds, which allow to bring back the problem to a Kaluza-Klein reduction. Both the zeta-function approach and the transmission coefficient approach are taken into account. A comparison between the two methods is also provided, as well as a comparison with WKB results. In the case of non-zero temperature of the geometric background, we also discuss thermal effects on the discharge process.ArXiv ePrint: 0906.1520 JHEP08(2009)028 determines a negative energy potential which at classical level must be discarded. However, at quantum level, negative energy states must be included, and a quantum interpretation to this couple of potentials can be given. The positive energy potential determines the allowed positive energy states, whereas the negative energy potential determines the allowed negative energy states. The usual separation of these states occurring in absence of external fields is not ensured a priori, and there can be regions where an overlap of positive and negative states for the particle is allowed, i.e. the Klein paradox takes place. In these level-crossing regions, by means of tunneling between negative and positive states, pair production of charged particles can take place with a rate determined by the transmission probability for the particle to cross the forbidden region between the two potentials, and can be computed e.g. in the WKB approximation.We improved this semiclassical picture in the case of anti de Sitter Reissner-Nordström black holes showing that the potentials have a direct interpretation at the quantum level without referring to the classical H-J equation [11]. Then, for the class of de Sitter Reissner-Nordström black holes we found that level-crossing is always present, due to the peculiar occurrence of both a black hole event horizon and a cosmological event horizon [12], and we also considered a particular limit case, when the black hole horizon radius r + equates the cosmological horizon radius r c : the Nariai black hole [13][14][15]. The aforementioned class of solutions contains further limit cases, corresponding to the extremal cases r − = r + = r c , which are called ultracold solutions of type I and II [13,15]. A careful WKB analysis was also performed for the Nariai case and the ultracold ones.Herein, we develop our analysis of the pair-creation process associated with the black hole electrostatic field, and fully exploit the fact that the aforementioned special backgrounds allow an exact calculation of the vacuum instability. As a consequence, we can provide for the first time, to our knowledge, exact results for the instability of 4D charged black holes. We point out that our backgrounds are of a special character: in all the cases the geometry involved is the one o...
A new process, the Hot Wire Cell method, was developed and successfully used to grow polycrystalline silicon thin films at a low temperature and high growth rate. In the Hot Wire Cell method, reactant gases are decomposed as a result of reacting with a heated tungsten filament placed near to a substrate and polycrystalline silicon films can be deposited at a growth rate of 1.2nm/s without hydrogen dilution and 0.9nm/s with the use hydrogen dilution. The film crystallinity changed from amorphous to polycrystalline due to the addition of hydrogen, thus hydrogen dilution was effective for improving film crystallinity. Furthermore, we obtained (220) oriented polycrystalline silicon thin films with a 90% crystal fraction by the use of hydrogen dilution. These results showed that the Hot Wire Cell method is promising for the deposition of device-grade polycrystalline silicon films for photovoltaic applications.
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