Highly-doped Silicon Research Articles

Integration of a carbon nanotube based electrode in silicon microtechnology to fabricateelectrochemical transducers

An original approach was developed and validated for the fabrication of a carbon nanotube(CNT) electrode synthesized directly onto a carbon buffer thin film deposited on a highlydoped monocrystalline silicon surface. The buffer layer of amorphous carbon thin film wasdeposited by physical vapour deposition on the silicon substrate before CNTsynthesis. For this purpose, nickel was deposited on the carbon buffer layer byan electrochemical procedure and used as a catalyst for the CNT growth. TheCNT synthesis was achieved by plasma enhanced chemical vapour deposition(PECVD) in an electron cyclotron resonance (ECR) plasma chamber using aC2H2/NH3 gas mixture. In order to evaluate the electrochemical behaviour of the CNT-basedelectrode, the carbon layer and the silicon/carbon interface were studied. The resultingbuffer layer enhanced the electronic transport from the doped silicon to the CNTs. Theelectrode surface was studied by XPS and characterized by both SEM and TEM. Theelectrochemical response exhibited by the resulting electrodes modified with CNTs was alsoexamined by cyclic voltammetry. The whole process was found to be compatible withsilicon microtechnology and could be envisaged for the direct integration of microsensors onsilicon chips.

Templated i-PVD of Metallic Nanodot Arrays

The results of numerical simulation of plasma-based, porous, template-assisted nanofabrication of Au nanodot arrays on highly-doped silicon taking into account typical electron density of low-temperature plasma of 10 17 -10 18 m -3 and electron temperature of 2-5 eV are reported here. Three-dimensional microscopic topography of ion flux distribution over the outer and inner surfaces of the nanoporous template is obtained via numerical simulation of Au ion trajectories in the plasma sheath, in the close proximity of, and inside the nanopores. It is shown that, by manipulating the electron temperature, the cross-sheath potential drop, and by additionally altering the structure of the nanoporous template, one can control the ion fluxes within the nanopores, and eventually maximize the ion deposition onto the top surface of the developing crystalline Au nanodots (see top panel in the figure). In the same time, this procedure allows one to minimize amorphous deposits on the sidewalls that clutter and may eventually close the nanopores, thus disrupting the nanodot growth process, as it is shown in the bottom panel in the figure on the right.

Porous silicon Bragg reflectors with sub-micrometer lateral dimensions

Bragg reflectors with widths down to 300 nm have been fabricated in porous silicon. This was achieved by irradiation of highly-doped p-type silicon with a focused beam of high-energy ions in a channeled alignment, in which the beam is aligned with a major crystallographic direction. The reflected colour is controllably tuned across the visible spectrum by varying the ion irradiated dose. The depth distribution of ion induced defects differs in channeled alignment compared to random beam alignment, resulting in the hole current during subsequent anodisation being more confined to narrower lateral regions, enabling different reflective wavelengths to be patterned on a sub-micron lateral scale. This work provides a means of producing high-density arrays of micron-size reflective colour pixels for uses in high-definition displays, and selectively tuning the wavelengths of porous silicon Fabry-Perot microcavities across the visible and infra-red ranges for optical communications and computing applications.

Comparative analysis of the DC performance of DG MOSFETs on highly-doped and near-intrinsic silicon layers

A comparison of dc characteristics of fully depleted double-gate (DG) MOSFETs with respect to low-power circuit applications and device scaling has been performed by two-dimensional device simulation. Three different DG MOSFET structures including a conventional N+ polysilicon gate device with highly doped Si layer, an asymmetrical P+/N+ polysilicon gate device with low doped Si layer and a mid-gap metal gate device with low doped Si layer have been analysed. It was found that DG MOSFET with mid-gap metal gates yields the best dc parameters for given off-state drain leakage current and highest immunity to the variation of technology parameters (gate length, gate oxide thickness and Si layer thickness). It is also found that an asymmetrical P+/N+ polysilicon gate DG MOSFET design offers comparable dc characteristics, but better parameter immunity to technology tolerances than a conventional DG MOSFET.

Characterisation of oxygen and oxygen-related defects in highly- and lowly-doped silicon

In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C– V) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).

Wet-Process Molecular Planting in A Specific Site on Silicon with Si-C Covalent Bonds

ABSTRACTAlkyl monolayers anchored covalently on silicon were prepared through the reaction between 1-alkenes and hydrogen-terminated silicon (111) surfaces. The 2D-patterning of the surface was done by local oxidation with an atomic force microscope (AFM) and 3D-molecular assemblies were fabricated by immobilization of molecules in a specific site of the patterned surface. The surfaces were anodized with a contact-mode AFM by applying a positive bias voltage to the surface with respect to the platinum-coated cantilever under ambient conditions, which resulted in nanometer-scale oxidation of surfaces. The anodized areas were etched and terminated with hydrogen atoms by NH4F solution, in which we could immobilize various molecules having C=C bonds. We put arylamine molecules to which organic dyes such as fluoroscein were anchored. The intensity of luminescence varied depending on dopant concentration of substrates. Luminescence was very weak on highly-doped silicon possibly due to effective energy transfer from dyes to substrates. The method demonstrated is one of the promising ways to fabricate 3D-assemblies of molecular-scale electronic devices with a stable interface on silicon.

Measurement of optical properties of highly doped silicon by terahertz time domain reflection spectroscopy

Optical properties of doped silicon wafers have been measured by means of terahertz time domain reflection spectroscopy. A method is proposed to obtain the relative phase by reflection accurately. By using this method, the relative phase is obtained within an error of less than 10 mrad at 1 THz. The experimentally obtained complex conductivity of relatively high-doped silicon (ρ=0.136 Ω cm) in the terahertz region agrees with the simple Drude model.

Silicon-platinum silicide Schottky barriers with a highly-doped surface layer

The spectral characteristic of infrared silicon–platinum silicide Schottky barrier photodetectors is shifted to the long wavelength region due to a highly-doped surface silicon layer produced by recoil boron implantation. The dependence of the resulting highly-doped layer parameters on high-energy boron-ion implantation regimes is studied experimentally. Energy-band diagrams and reduction of the barrier height are calculated for p-Si–PtSi structures with highly-doped surface layers produced by molecular-beam epitaxy and recoil implantation.

Evidence for vacancy percolation in highly-doped silicon

The extreme dopant diffusivities observed in silicon for donor concentrations in excess of 2×1020cm−3 have recently been explained by a vacancy percolation model proposing that a network of fast diffusion paths is formed when the average distance of the donors becomes equal to or less than the fifth nearest-neighbour distance. Here, we report on evidence by means of119Sn Mossbauer spectroscopy for the postulated high vacancy concentration in the percolation cluster.

Laser-Chemical Deposition and Etching on the Metallization Level of Integrated Circuits

AbstractLaser-controlled chemical deposition and etching techniques were used to modify integrated circuits. This work used a pulsed laser to initiate and control the etching, by chlorine gas, of aluminum conductors. New conducting paths were then formed by laser-chemical vapor deposition of highly-doped silicon from silane and diborane. Improved conductivity of laser-deposited connectors was achieved by the selective deposition of tungsten on the silicon. These techniques were used to “rewire” an integrated circuit allowing the full evaluation of the corrected circuit design.

An empirical fit to minority hole mobilities

Minority hole mobilities in highly-doped n-type silicon are determined by electron-beam-induced current measurements. They are used in conjunction with existing data taken from the literature to derive an empirical expression for the minority hole moblility as a function of majority-carrier density 1014cm-3≤ N D ≤ cm-3. It is anticipated that this empirical fit will be valuable in device modeling.