N-type Silicon Films Research Articles

Formation of Epitaxial Heavy-doped Silicon Films by PECVD Method

Plasma-enhanced CVD (PECVD) epitaxy at 200 °C was used to deposit heavy doped n-type silicon films. Post-annealing by rapid thermal processing was applied to improve the properties of the epitaxial layer. By analyzing the Raman spectra and the imaginary part of the dielectric constant spectra of the samples, it was found that high-quality heavy-doped epitaxial n-type silicon layer can be obtained by optimizing the parameters of the PECVD depositing process. Reducing the electrodes distance of the PECVD had a great effect on the crystallzation of the epitaxialed n-type silicon films. Sillicon films with high-crystallization were obtained with the electrodes distance of 18 mm. Post-annealing process can improve the crystallization and reduce the resistance of the epitaxial films. In our research, it was found that the sheet resistance (R□) of the post-annealed films with thickness of about 50 nm has a simple relationship with RPH3/SiH4 (ratio of the flow rate of PH3 and SiH4) of the PECVD processing: R□=-184-125 lg(RPH3/SiH4). In the end, high-quality epitaxial n-type silicon film was obtained with R□ of 15 Ω/□ and thickness of ~50 nm.

Low temperature deposition of polycrystalline silicon thin films on a flexible polymer substrate by hot wire chemical vapor deposition

For the applications such as flexible displays and solar cells, the direct deposition of crystalline silicon films on a flexible polymer substrate has been a great issue. Here, we investigated the direct deposition of polycrystalline silicon films on a polyimide film at the substrate temperature of 200°C. The low temperature deposition of crystalline silicon on a flexible substrate has been successfully made based on two ideas. One is that the Si–Cl–H system has a retrograde solubility of silicon in the gas phase near the substrate temperature. The other is the new concept of non-classical crystallization, where films grow by the building block of nanoparticles formed in the gas phase during hot-wire chemical vapor deposition (HWCVD). The total amount of precipitation of silicon nanoparticles decreased with increasing HCl concentration. By adding HCl, the amount and the size of silicon nanoparticles were reduced remarkably, which is related with the low temperature deposition of silicon films of highly crystalline fraction with a very thin amorphous incubation layer. The dark conductivity of the intrinsic film prepared at the flow rate ratio of RHCl=[HCl]/[SiH4]=3.61 was 1.84×10–6Scm−1 at room temperature. The Hall mobility of the n-type silicon film prepared at RHCl=3.61 was 5.72cm2V−1s−1. These electrical properties of silicon films are high enough and could be used in flexible electric devices.

RF power dependence of the properties of n-type nanocrystalline silicon films deposited by a low-frequency inductively coupled plasma

Nanocrystalline n-type silicon films are deposited by a low-frequency inductively coupled plasma at a low H2 dilution, low working pressure of 2.0 Pa and low substrate temperature of 150 °C. The radio frequency (RF) power is set in the range 1000–1800 W. The RF power dependence of the structural, optical and electrical properties of the films is systematically studied. The x-ray diffraction patterns of the films present a (1 1 1)-preferred orientation when the RF power is increased from 1000 to 1800 W. The crystalline volume fraction of the films changes from 51% to 82% while the deposition rate of the films increases from 21 to 36 nm min−1. The UV–VIS spectra show that the optical band gap is in the range 1.4–1.6 eV. Two characteristic hydrogen-related modes located at ∼630 and ∼2100 cm−1 are observed. The carrier concentration of the films ranges from 0.9 × 1019 to 1.1 × 1020 cm−3 depending on the applied RF power. When the RF power is increased, the electron density is increased and the Debye length is decreased while the electron temperature remains nearly constant. The doping mechanism of the present n-type nanocrystalline silicon films is revealed.

GOX-functionalized nanodiamond films for electrochemical biosensor

The importance of nanodiamond in biological and technological applications has been recognized recently, and applied in drug delivery, biochip, sensors and biosensors. Under this investigation, nanodiamond (ND) and nitrogen doped nanodiamond (NND) were deposited on n-type silicon films, and later functionalized with enzyme Glucose oxidase (GOX). The GOX functionalized doped and undoped ND films were characterized using combination of several techniques; i.e. FTIR spectroscopy, Raman spectroscopy, atomic force microscopy (AFM) and electrochemical techniques. ND/GOX and NND/GOX thin films on n-type silicon have been found to provide sensitive glucose sensor. GOX has been chosen as a model enzyme system to functionalize with ND at molecular level to understand the glucose biosensor.

Glucose Oxidase-Functionalized Nanodiamond Films for Biosensor Application

ABSTRACTThe importance of nanodiamond in biological and technological applications has been recognized, and applied in drug delivery, biochip, sensors and biosensors. Nanodiamond (ND) and nitrogen doped nanodiamond (NND) films were deposited on n-type silicon films, and later functionalized with enzyme glucose oxidase (GOX). Functionalized electrode has been characterized using different techniques; i.e.fourier transform spectroscopy (FTIR) -, Raman spectroscopy, atomic force microscopy (AFM) and electrochemical techniques, respectively. Under this work, the ND/GOX and NND/GOX electrodes have demonstrated providing sensitive glucose concentration response. Besides, the cytotoxic effects of the NDs have been studied in vitro. Human Embryonic Kidney 293 (HEK293) cells are cultured in the presence of the films then toxicity has been detected using MTT-based cytotoxicity assays utilizing 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT). The final results for MTT assays are quantified by spectrophotometry using a plate reader at 570 nm As-prepared nanodiamond has been found to be stable , biocompatible and useful for biosensing applications. A linear response of the enzyme based electrode to glucose concentration is also observed from 1-8 x mM before saturation condition close to 10mM has been observed.

Improvement of Electrochemical Capability of Sputtered Silicon Film Anode for Rechargeable Lithium Batteries

Abstract To improve the electrochemical properties of the silicon film anode in lithium cells, we prepared three types of silicon based-films, i.e., intrinsic silicon, n-type silicon, and Ag10Si90 binary films using r.f. magnetron sputtering. Based on galvanostatic charge–discharge tests and a.c. impedance measurements, the n-type silicon film and Ag10Si90 binary film cells exhibited a superior cycle life and lower electrochemical resistance compared with the intrinsic silicon film cell. The potential variation in the electrochemical alloying/de-alloying reactions of the Ag10Si90 binary film with lithium was different from that of the intrinsic silicon film, meaning that the Ag ingredient in the binary film affected the charge–discharge reaction. Furthermore, when a Ni plate roughened by chemical etching was used as a substrate, the Ag10Si90 film anode demonstrated an excellent capacity retention during 400 cycles with a high discharge capacity of >200 μA h cm−2 (corresponding to 1500 mA h g−1) at 0.5 mA cm−2 (2.5 C).

Properties of Nano-crystalline n-type Silicon Films Produced by Hot Wire Plasma Assisted Technique

ABSTRACTIn this work, we present the properties of n-type silicon films obtained by hot wire plasma assisted technique produced at different rf power and gas flow rate. The films were produced at a filament temperature of 2000°C and the rf power was varied from 0W to 200W while gas flow rate was varied from 15 to 100sccm keeping rf power at 50W. In this flow rate range, the growth rate of the films varied from 5Å/s to 250Å/s and the corresponding electrical room dark conductivity varied from 10−2 to 10(Ωcm)-1. On the other hand, we observed that the electrical conductivity increased from 2 to 6(Ωcm)-1, and the Hall mobility from 0.1 to 2cm2/V.s as rf power change from 0W to 200W. The infrared, EDS and XPS analyses revealed the existence of oxygen incorporation, which is not related to post-deposition oxidation. The X-ray diffraction and [.proportional]Raman data show the presence of Si crystals in the films structure and the SEM micrographs reveal a granular surface morphology with grain sizes lower than 60nm.

N-Type Silicon Films Produced by Hot Wire Technique

ABSTRACTThe role of the deposition pressure (p) and the type of filaments (tungsten, W or tantalum, Ta) used to produce large area (10cm×10cm) n-type Si:H films by hot wire chemical vapour (HW-CVD) deposition technique was investigated. The data show that the electro-optical properties of the films produced are dependent on the gas pressure used. In the pressure range of 1×10-3 Torr to 1.0 Torr, the room dark conductivity (σd) varies from 1×10-8 to 2 S/cm for films produced at the same hydrogen dilution and filament temperature (Tfil.). On the other hand, the hydrogen concentration (CH) decreases from 10% to 2%, while the growth rate (R) shows an exponential increase, from 1 to 9 Å/s. The SIMS analysis, within the detection limits, does not reveal the existence of any significant W or Ta contamination in the films produced.

Negative resistance switching in near-perfect crystalline silicon film resistors

This paper describes negative resistance switching in n-type silicon film resistors which contain linear arrays of grain boundaries. These linear arrays have been predictably located in the active region by a laser recrystallization procedure. The grain boundaries are made to bisect the resistors. Effects of parameters such as grain boundary number and grain-dopant concentration have been examined. We show that quasisaturated and asymmetrical I–V characteristics are exhibited by our resistors. This is evidence that the voltages across the depletion region and across the grain boundary layer are not equally divided on each side of the junction, and that dopants are nonuniformly incorporated in the grains during laser recrystallization.

Growth and properties of silicon films on aluminum-nitride films on sapphire

Epitaxial layers of silicon have been grown on aluminum-nitride films on sapphire by vapor-phase deposition using pyrolysis of silane. The structure of the silicon films is examined by the reflection electron diffraction technique and shown to be a single crystal of orientation (100)Si∥ (112̄0)AlN∥ (011̄2)Al2O3. Lattice matching between Si and AlN along orthogonal axes of [100] Si are 0.78 and 9.0%, respectively. The growth and electrical properties of silicon films are described in some detail. Resistivity and mobility of p-type and n-type silicon films have been measured as functions of temperature. The maximum mobility of 150 cm2/V sec has been obtained for film thickness between 1 and 4 μm. The aluminum autodoping effect upon these films is found to be higher than that of silicon films on sapphire used as control samples.