Electrical properties of B-doped polycrystalline silicon thin films prepared by rapid thermal chemical vapour deposition

In this paper, about 30 mu m thick B-doped polycrystalline silicon (poly-Si) thin films were deposited on quartz substrates, n-type single crystalline silicon wafers and p(++)-type poly-Si ribbons by a rapid thermal chemical vapour deposition system in a temperature range from 1000 to 1150 degrees C. Activation energy measurement and room temperature/temperature dependent Hall effect measurement were performed on the poly-Si thin films prepared on the former two kinds of substrates, respectively. It seems that the electrical properties of as-prepared poly-Si thin films could be qualitatively explained by Seto's grain boundary (GB) trapping theory although there is a big difference between our samples and Seto's in gain size and film thickness etc. The experimental results reconfirm that GB itself is a kind of most effective recombination center with trapping level near the midgap and trapping state density in the order of 1012 cm(-2) magnitude. Electron beam induced current measurements on the poly-Si thin films prepared on the poly-Si ribbons also show that severe recombination occurs at the positions of GBs. (c) 2005 Elsevier B.V All rights reserved.

SPECTROSCOPIC INVESTIGATION OF HYDROGEN-DOPANT COMPLEXES IN BULK P-TYPE AND IMPLANTED N-TYPE CRYSTALLINE SILICON

Infrared absorption experiments have been performed on hydrogenated and deuterated bulk boron- and aluminum-doped-Si and implanted P, As, and Sb donors in silicon. A first evidence of complex formation in bulk p-type Si is obtained and the spectra confirm the anomalous 3.3-cm-1 deuterium frequency shift with respect to boron isotopes. The ratio of the D-B-11 and D-B-10 peak areas is found to be the same as that of the two boron isotopes natural abundance. In donor-implanted silicon, a quantitative analysis of the obtained data has allowed a rough estimate of the passivating rate due to diffusing deuterium. While the frequencies of the various vibrational lines are found to be in agreement with those reported in the literature, the data on the broad line at 1660 cm-1 (H) or 1220 cm-1 (D) seem to suggest an assignment of this peak to a complex in the bulk involving some type of defect due to the implantation process.

High-frequency capacitance-voltage characteristics of amorphous (undoped)/crystalline silicon heterostructures

A numerical procedure is presented for calculating high-frequency capacitance variation with bias in amorphous (undoped)/crystalline silicon heterojunction. The results of the model calculations using this procedure have been reported, for different p silicon substrates. These have been compared with the corresponding capacitance variations in the other limiting case, in which the heterostructure acts like an MIS structure. The effect of interface states on the capacitance characteristics has also been studied. In the second part, we report the results of 1 MHz capacitance measurements on various amorphous (undoped)/crystalline silicon heterostructures.

On the anharmonic vibrations in crystalline silicon

Using a total of 1052 Bragg reflections of silicon, an X-ray investigation has been carried out to deduce the anharmonic thermal parameter beta, apart from the estimation of the harmonic contribution of the thermal vibration at room temperature. Reflections of type h + k + l = 4n, and 4n +/- 1 were used to estimate these parameters using MoKalpha radiation and a Nonius CAD-4 X-ray diffractometer. We obtain B(Si) = 0.451 (0.008) angstrom2 and beta(Si) = 0.279(2.630) eV angstrom-3 with R = 3.12%. The present B and beta values are in very good agreement with the earlier studies.

The formation and electronic structures of 3d transition-metal atoms doped in silicon nanowires

Using first-principles methods, we systematically study the mechanism of defect formation and electronic structures for 3d transition-metal impurities (V, Cr, Mn, Fe, and Co) doped in silicon nanowires. We find that the formation energies of 3d transition-metal impurities with electrons or holes at the defect levels always increase as the diameters of silicon nanowires decrease, which suggests that self-purification, i.e., the difficulty of doping in silicon nanowires, should be an intrinsic effect. The calculated results show that the defect formation energies of Mn and Fe impurities are lower than those of V, Cr, and Co impurities in silicon nanowires. It indicates that Mn and Fe can easily occupy substitutional site in the interior of silicon nanowires. Moreover, they have larger localized moments, which means that they are good candidates for Si-based dilute magnetic semiconductor nanowires. The doping of Mn and Fe atom in silicon nanowires introduces a pair of energy levels with t(2) symmetry. One of which is dominated by 3d electrons of Mn or Fe, and the other by neighboring dangling bonds of Si vacancies. In addition, a set of nonbonding states localized on the transition-metal atom with e symmetry is also introduced. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3000445]

Thermally tunable optical filter with crystalline silicon as cavity

A novel method to fabricate a thermally tunable filter with a tuning range of 26 nm from 1.504 to 1.530 mum is reported. The high-reffectivity bottom mirror is deposited in the hole formed by anisotropically etching in the basic solution from the backside of the slice with the buried SiO2 layer in silicon-on-insulator substrate as the etching-stop layer. Because of the formation of the mesa and the removing of the substrate of the hole, the power from the metal heater can be more effectively consumed in the crystalline silicon cavity. So it lowers the power consumption and the filter has a higher tuning range. (C) 2004 Elsevier B.V. All rights reserved.

Enhanced near-infrared photoluminescence from isoelectronic luminescent centers in sulfur-implanted silicon with copper or silver coimplantation

Enhanced near-infrared photoluminescence (PL) from sulfur-related isoelectronic luminescent centers in silicon was observed from thermally quenched sulfur-implanted silicon in which additional copper or silver ions had been coimplanted. The PL from the sulfur and copper coimplanted silicon peaked between 70 and 100 K and persisted to 260 K. This result strongly supports the original conjecture from the optical detection of magnetic resonance studies that the strong PL from sulfur-doped silicon comes from S-Cu isoelectronic complexes [Frens , Phys. Rev. B 46, 12316 (1992); Mason , ibid. 58, 7007 (1998).]. (c) 2007 American Institute of Physics.

Hydrogen passivation of multi-crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.

Comparative study of the surface passivation on crystalline silicon by silicon thin films with different structures

Si thin films with different structures were deposited by plasma enhanced chemical vapor deposition (PECVD), and characterized via Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The passivation effect of such different Si thin films on crystalline Si surface was investigated by minority carrier lifetime measurement via a method, called microwave photoconductive decay (mu PCD), for the application in HIT (heterojunction with intrinsic thin-layer) solar cells. The results show that amorphous silicon (a-Si:H) has a better passivation effect due to its relative higher H content, compared with microcrystalline (mu c-Si) silicon and nanocrystalline silicon (nc-Si). Further, it was found that H atoms in the form of Si-H bonds are more preferred than those in the form of Si-H-2 bonds to passivate the crystalline Si surface. (C) 2009 Elsevier B.V. All rights reserved.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.