Papers by Keyword: n-Type

Abstract: We have presented the results of detailed studies of oxygen vacancy and niobium (Nb) substituted spinel Li4Ti5O12 (LTO) materials using first-principles method within the framework of the density functional theory (DFT). We have shown that the ground state of oxygen vacancy and Nb substituted LTO is paramagnetic (PM), and the Nb substitution is most stable on the 16d sites of both the Li and Ti ions. We have indicated that the Nb substitution in the 16d site of Li ion become the n-type metallic material. But the oxygen vacancy containing NbT i substituted LTO is changed from the p-type to the n-type, as increased a concentration of Nb ions.

Abstract: In order to understand the contribution of various metals in the formation of ohmic contacts, Ni/Al/Ti ohmic contacts on n-type 4H-SiC in terms of a different annealing temperature and Ti composition are investigated, which is more difficult to form than p-type ohmic contact. The formation of the Ni/Al/Ti metal alloy system is much more sensitive to metal composition than annealing conditions. With the increase of metal composition, the contact with a high Ti content yields a lower specific contact resistivity compared with the low Ti contact. The annealed surface morphology and phase resultants were examined by scanning electron microscopy (SEM) and atomic force microscope (AFM), respectively. With the increase of Ti components, the surface morphology of the samples becomes more uniform and smoother, while the surface roughness remains unchanged. It implies that Ti metal can not only reduce the ohmic resistance, but also protect the surface of the sample and maintain the roughness.

Abstract: In wafer-based silicon solar cell technology cleaning of silicon surfaces has so far been treated without much interest – the cheapest, simple solution, which means mostly rinsing with or dipping into diluted acids (HCl, HF), was the best. Whatever worked was rarely further investigated. Hence, not much work has been published in the field of contamination control and cleaning process optimization and development. With solar cell efficiencies increasing and processes becoming more and more sensitive, the interest in quality control and optimization of cleaning processes is rising.

Abstract: Nanocrystalline ZnO films were deposited by rf reactive magnetron sputtering. The films were characterized by reflection high-energy electron diffraction, X-ray photoelectron spectroscopy and gas sensing measurements. It was found that annealing of the film enabled to invert its conductivity type. Thus, as-deposited ZnO film showed p-type conductivity while annealed film showed n-type conductivity behavior. The p-and n-type conductivities of the films obtained by gas sensing measurements have been confirmed by XPS results. The gas sensing properties of the films were investigated upon exposure to 10 ppm of NO₂ at 22°C and exhibited good sensitivity with fast response and recovery times. The sensor response to NO₂ was found to be profoundly dependent on the conductivity behavior of the film.

Abstract: By conventional production-line process, n-type Al-doped rear junction solar cell could be easily fabricated without any other equipment and process. Since the properties of n-type silicon material are different to that of p-type silicon material and the junction is placed at the back, the process parameters should be optimized theoretically to assess the efficient potential. By modeling cells using PC1D software, the effect of some process parameters on the properties of n-type base solar cells were studied, including base resistivity, bulk lifetime, front surface field and recombination rate of front surface. The key parameters were identified and the potential industrial efficiency was calculated.

Abstract: The doping of Cu in the BaSi₂ films grown by molecular beam epitaxy (MBE) with various Cu concentrations for the suitability of the solar cells was studied in this paper. The main objective of the present work is to investigate and compare the carrier concentration of Cu-doped BaSi₂ films grown with different Cu Knudsen cell temperatures and qualify as a potential candidate for more efficient solar cells. The reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) measurements and secondary ion mass spectroscopy (SIMS), were used to determine the structure, depth profile and composition of the grown samples. The electrical properties like resistivity as well as carrier concentration were measured by using a four point probe method and Van der Pauw technique, respectively. During the MBE growth, different temperatures for Cu Knudsen cell ranging from 800 to 1200 °C were chosen and the optimum growth condition for both heavily doped n-type as well as p-type in the MBE was investigated. In our previous work, the Al, Sb doped BaSi₂ were used as a potential candidate for the formation of pn-junction for solar cells, but the result was not encouraging one due to diffusion and segregation problems in the surface and BaSi₂/Si interface regions. In the present work n-type BaSi₂ layers with their dopant atoms uniformly distributed in the grown layers for the formation of high-quality of BaSi₂ pn-junction with single crystal nature were successfully developed. The realizations to develop cost effective and more efficient solar cells are inevitable for both terrestrial as well as space applications.

Abstract: In this paper, the issues related to in-situ doping of silicon carbide (SiC) semiconductor during epitaxial growth are reviewed. Some of these issues can find solution by using an original approach called vapour-liquid-solid (VLS) mechanism. In this technique, the SiC seed is covered by a Sibased melt and is fed by propane in order to growth the epitaxial film. Using Al-Si melts and temperatures as low as 1100°C, very high p type doping was demonstrated, with a record value of 1.1021 at.cm-3. It leads to very low contact resistivity and even to metallic behaviour of the SiC deposit even at low temperature. Using Ge-Si melts, non intentionally low doped n type layers are grown. By forming Si-containing liquid droplets on a SiC seed, one can extrapolate this VLS growth to selective epitaxial growth (SEG). Such approach was successfully applied for both Al and Ge-based systems in order to form p+ and n doped areas respectively.

Abstract: A multiple data point version of the industry standard, two data point raster-changing procedure is employed to measure low levels (< 1 x 1017 atoms/cm3) of nitrogen (N) in silicon carbide (SiC) by SIMS (Secondary Ion Mass Spectrometry). A current-changing procedure is also employed. Together, these are used evaluate the assumptions of the standard method, to separate and measure the components of background signal, and to improve upon the precision and accuracy of the standard method. The risk of poor precision in the two-point method is demonstrated, as is the improvement provided by the multiple-point method. Results show that, in addition to the wellknown N memory background, adsorption background can contribute significantly to the N signal. In general, establishing the presence of adsorption gas in this way can be used to warn of the presence of ionization background, which is not measurable per se.

Abstract: In order to understand carrier statistics in phosphorus-doped n-type diamond, electron statistics involving compensation and deep-dopant effect are theoretically analyzed. For n-diamond with a compensation ratio (c) larger than 1x10-4, the electron concentration (n) at room temperature (RT) is insensitive to the donor concentration (ND) and reduced with increasing the c value. On the other hand, for diamond with a c value smaller than 1x10-4, the n value at RT increases with increasing the ND value and is insensitive to the c value. Similarly, the length of Debye tailing (ln) at RT is reduced with increasing the c value for n-diamond with c>1x10-4 and is insensitive to the c value for n-diamond with c<1x10-4. However, it is found that an increase of temperature is effective to increase the n value and to reduce the ln value. The n value as large as 1015 cm-3 and the ln value as small as 100 nm are expected to be achieved at an elevated temperature of 473 K.