P-doped Silicon Research Articles

Thermal emissivity of carbon coated p-doped silicon stencil masks for ion projection lithography

The determination and optimization of the thermal emissivity is an essential topic for ion projection lithography (IPL), one of the most promising candidates for the next generation lithography. In order to determine the thermal emissivity of stencil masks, infrared transmittance and reflectance spectra have been measured in the spectral region 100–6000 cm−1. The infrared absorption could be mainly described by a simple Drude model. The high quality of the silicon masks became evident in a Fano resonance of the optical phonons with the intervalence-band absorption and the free-carrier continuum. The obtained values of 0.5 to 0.6 for the emissivities have been used to model the thermomechanical response of the IPL exposure station. Radiation cooling is sufficient to cool the stencil mask to room temperature at the desired ion fluxes which cause heat generation rates of 8.5–10 mW cm−2. At high irradiation intensities, the membrane distortions have to be minimized instead of optimizing the uniformity of the temperature distribution. For 7 mW cm−2, temperature variations of 3.5 K are needed to keep mask distortions below 10 nm.

Formation and passivation kinetics of gold-hydrogen complexes in n-type silicon

Reverse- and zero-bias annealing kinetics of Au-related deep levels in Au diffused P-doped silicon hydrogenated by wet chemical etching, have been determined. The dynamic behavior of these deep levels can enable an estimation of the number of hydrogen atoms in the defects. Differences in the dynamic behavior during both reverse- and zero-bias annealing supports the suggestion that gold and hydrogen form at least two different electrically active complexes (AuH and AuH2) in n-type silicon.

Photoelectron emission microscopy of ultrathin oxide covered devices

Photoelectron emission microscopy (PEEM) has been used to investigate simple device structures buried under ultrathin oxides. In particular, we have imaged Au–SiO2 and p-type Si–SiO2 structures and have demonstrated that PEEM is sensitive to these buried structures. Oxide overlayers ranging up to 15.3 nm were grown by systematically varying the exposure time of the structures to a plasma-enhanced chemical-vapor deposition process. The change in image contrast as the oxide thickness increases was used to quantify the inelastic mean-free path of low-energy photoelectrons (∼1 eV) in amorphous silicon dioxide. For Au structures we find that the dominant mean-free path for photoelectrons in the overlying oxide is about 1.18±0.2 nm. Yet, we find a residual observable signal from the buried Au structure through roughly 13 oxide attenuation lengths. The signal attenuation from the Au can be explained by the spread of the photoelectron energies and the energy dependence of the electron–phonon interaction. Similar intensity attenuation behavior is also seen from heavily p-doped silicon (1020 cm−3) regions, but the signal is only observable through roughly 3.0 nm of oxide, and the signal from the 1018 cm−3 regions is not detectable through the thinnest oxide layer of approximately 2.5 nm. Here, the energy spread (∼2.0 eV) is more narrowly distributed about the phonon loss energies, leading to the observed attenuation behavior from heavily p-doped silicon.

Electrochemical etch-stop technique for silicon membranes with p- and n-type regions and its application to neural sieve electrodes

In this study the field effects on electrochemically controlled silicon etching in KOH during three- and four-electrode pn etch-stop have been investigated. When a p-doped bulk area is surrounded by n-doped silicon and the n-doped silicon is electrochemically passivated, small lines of bulk silicon in between the n-doped silicon would not etch. The size of the bulk silicon that did not etch could be moderated by the applied potential on the n-doped silicon during pn etching. For the three-electrode system the size of the electric field passivated bulk silicon could be controlled for line widths ranging between 60 and 100 μm. When a four-electrode system was used and the p-doped bulk silicon was forced to a more negative potential, it was possible to etch lines of bulk silicon down to 40 μm widths. This field-restricted pn etch-stop can be used for fabricating thin membrane structures with densely spaced n-doped regions that can be individually addressed by electronics. One application is the fabrication of neural sieve electrodes which comprise a pn etch-stopped membrane containing several phosphorous-doped individually addressable recording electrodes.

Scanning impedance microscopy of an active Schottky barrier diode

Electrostatic force sensitive scanning probe microscopy is used to quantify dc and ac transport properties of an active Schottky barrier diode. Scanning surface potential microscopy (SSPM) of the laterally biased device is used to quantify the potential drop at the metal–semiconductor interface. Ramping the lateral bias allows the local voltage and I–V characteristics of the diode to be reconstructed. Scanning impedance microscopy (SIM) demonstrates the phase and amplitude change of voltage oscillations across the interface. The frequency dependence of voltage phase shifts across the interface defines the appropriate equivalent circuit for the reverse biased junction. Excellent agreement between junction capacitance obtained from SIM measurements and impedance spectroscopy is demonstrated. Variation of the dc component of lateral bias in SIM yields the local capacitance–voltage characteristics of the junction. SIM contrast of grain boundaries in p-doped silicon was interpreted in terms of minority carrier generation in the interface region. The combination of SSPM and SIM provides an approach for the quantitative analysis of local dc and ac transport properties which were demonstrated for a Schottky diode but can be applied to any semiconductor device.

Morphology and structure of nanocrystalline p-doped silicon films produced by hot wire technique

In this paper we report results of nanocrystalline p-doped silicon films produced by hot wire chemical vapour deposition technique with Ta filaments, using a pre-mixed gas containing silane, diborane, methane, helium and hydrogen. The data obtained show that the films produced exhibit good optoelectronic properties and show a surface morphology dependent on the filament temperature and hydrogen dilution. The increase in the filament temperature, keeping constant the hydrogen dilution (87%), promotes the preferential growth of the crystals in the {2 2 0} direction, giving rise to a pyramidal-like surface structure. This behaviour is observed by the SEM micrographs as well as by the micro-Raman and X-ray diffraction analyses. On the other hand, using a constant filament temperature, the increase in the hydrogen dilution contributes to an increase in both {1 1 1} and {2 2 0} diffraction peaks. Thus, by combining both filament temperature and hydrogen dilution the film surface can be controlled from a smooth to a pyramidal-like structure, without decreasing the crystalline fraction of the films. The structure and morphology is also reflected in the stability of the electrical dark conductivity. We observe that this property depends on the temperature range of the measurements and on the exposition time of films to the atmospheric conditions.

Photoelectrochemical characterization of p- and n-doped single crystalline silicon carbide and photoinduced reductive dehalogenation of organic pollutants at p-doped silicon carbide

In this work, the photoelectrochemical properties of single crystalline p- and n-SiC, now available from Cree Research, Inc., will be presented. 4H- and 6H-SiC were investigated by electrochemical impedance spectroscopy and cyclic voltammetry. Flatband potentials of p-SiC determined by application of the Mott–Schottky-relation varied from 1.8 to 2.5 V versus NHE depending on the C or Si face and the doping concentration of the single crystalline samples. The flatband potential of n-SiC was found to be −1.3 V vs. NHE. A nearly Nernstian dependence on the pH was found for both the n-SiC and the p-SiC-types. The onset of the cathodic photocurrent at p-SiC occurred with a large overpotential in aqueous solution. P-SiC was used as photocathode for the reductive dehalogenation of halogenated acetic acids due to its chemical stability, its highly energetic conduction band and the overvoltage for the hydrogen evolution. It was especially suitable for the reduction of less reducible chlorinated acetic acids in the aqueous phase. The dehalogenation of brominated acetic acids resulted in the complete release of bromine in form of bromide. The bromide yields were about 98%. In case of chlorinated acetic acids, the dehalogenation stopped at the level of monochloroacetic acid, since this halide was very slowly reduced.

Temperature dependence of optical and electronic properties of moderately doped silicon at terahertz frequencies

Complex conductivity of moderately P-doped silicon wafers (1.1±0.2 Ω cm at room temperature) has been measured by using a terahertz (THz) time-domain spectroscopy for the temperature and frequency ranges of 20–300 K and 0.2–1.1 THz, respectively. The strong frequency dependence of the complex conductivity due to the free carriers in the THz region is observed and it changes rapidly with temperature, which is interpreted in terms of the increase in mobility and freezing of the free carrier as analyzed by using the simple Drude model. The experimental data deviate slightly from the simple Drude model at low temperatures and becomes apparent with decreasing temperature.

Emission properties of an amorphous AlN:Cr3+ thin-film phosphor

Chromium-doped aluminum nitride (AlN:Cr) films were grown on p-doped silicon (111) by rf magnetron sputtering in a nitrogen atmosphere at a pressure of 10−4 Torr. Film thickness was typically 200 nm. After growth, the films were “activated” at ∼1300 K for 30 min in a nitrogen atmosphere. Films activated in this manner exhibit intense cathodoluminescence and photoluminescence emission. Spectral evidence demonstrates conclusively that the luminescent centers are Cr3+ ions.

Scanning Impedance Microscopy: From Impedance Spectra to Impedance Images

Abstract:Impedance spectroscopy has long been recognized as one of the major techniques for the characterization of ac transport in materials. The primary limitation of this technique is the lack of spatial resolution that precludes the equivalent circuit elements from being unambiguously associated with individual microstructural features. Here we present a scanning probe microscopy technique for quantitative imaging of ac and dc transport properties of electrically inhomogeneous materials. This technique, referred to as Scanning Impedance Microscopy (SIM), maps the phase and amplitude of local potential with respect to an electric field applied across the sample. Amplitude and phase behavior of individual defects can be correlated with their transport properties. The frequency dependence of the voltage phase shift across an interface yields capacitance and resistance. SIM of single interfaces is demonstrated on a model metal-semiconductor junction. The local interface capacitance and resistance obtained from SIM measurements agrees quantitatively with macroscopic impedance spectroscopy. Superposition of a dc sample bias during SIM probes the C-V characteristics of the interface. When combined with Scanning Surface Potential Microscopy (SSPM), which can be used to determine interface I-V characteristic, local transport properties are completely determined. SIM and SSPM of polycrystalline materials are demonstrated on BiFeO3 and p-doped silicon. An excellent agreement between the properties of a single interface determined by SIM and traditional impedance spectra is demonstrated. Finally, the applicability of this technique for imaging transport behavior in nanoelectronic devices is illustrated with carbon nanotube circuit.

Amorphous Nitride Alloys as Hosts for Rare-Earth Luminescent Ions.

ABSTRACTAmorphous alloys of aluminum-gallium nitride doped with erbium (Er) were deposited at 300 K. The compositions ranged from 19% Al to 86% Al with optical band gaps varying linearly with composition from 3.4 eV (GaN) to 6.2 eV (AlN). The films were deposited on p-doped silicon (111) by a dc/rf dual gun system in a nitrogen/argon atmosphere at a pressure of 4.8 milli-Torr. After growth the films were thermally “activated” at 1070 K for 10 minutes in a nitrogen atmosphere. The cathodoluminescence emission intensities decreased linearly with Ga composition. This dependence suggests that the higher energy transitions in the Er ion are quenched by transitions to the conduction band of the alloys.

A Device for Sublimation Molecular-Beam Deposition of Silicon Films

A device for sublimation molecular-beam deposition of P-doped silicon films on standard silicon wafers with diameters of up to 76 mm is described. Uniform deposition was performed through asymmetric arrangement of the sublimation source relative to the wafer, which was rotated about its axis.

In situ monitoring of the deposition of a-Si : H/c-Si heterojunctions by transient photoconductivity measurements

To investigate the relation between interface passivation and the performance of an a-Si:H/c-Si solar cell, we monitored the glow discharge deposition process of n-doped a-Si:H films on p-doped crystalline silicon in situ by transient photoconductivity measurements in the microwave frequency range (TRMC measurements). After the end of the deposition process, we also performed ex situ TRMC measurements of the heterojunctions. From three representative samples, we prepared solar cells and their performances were compared to the TRMC measurements.

Amorphous carbon films deposited by direct current-magnetron sputtering: Void distribution investigated by gas effusion and small angle x-ray scattering experiments

Amorphous carbon films were deposited by direct current-magnetron sputtering onto p-doped (100) silicon crystals and onto ultrapure aluminum foils at different argon pressures, ranging from 0.17 to 1.4 Pa. The film density was determined by the combination of the areal density, obtained from ion beam analysis, and the film thickness measured by a stylus profilometer. Film density decreased when the argon pressure used during deposition was increased. Gas effusion measurements indicated that the films deposited at low pressures are more compact than the films deposited at higher pressures. In the case of the latter, C2Hn effusion at temperatures as low as 250 °C indicated that they have an open structure that allows the evolution of large molecules. Small angle x-ray scattering results revealed an increase of the void density with increasing plasma pressure. Guinier plots show that these voids have a broad distribution of sizes, ranged from 7 to 26 Å, which is nearly independent of the plasma pressure. A direct correlation between film density and the open volume fraction in the films was found. These different film microstructures could be explained by the existence of different bombardment regimes during film growth: films deposited at lower plasma pressures are hard and dense, while soft films grown at higher pressures have an open microstructure.

Pyroelectric properties of Pb0.9La0.1TiO3 (PLT(10)) thin films on p-doped poly silicon

Pyroelectric properties of the PLT(10) thin film deposited on a p-doped poly-Si electrode have been studied by using the static measurement method. Measurement of the dielectric constant as a function of temperature shows the typical characteristics of a ferroelectric. The dielectric constant reaches a maximum at 295°C, which can be thought of as the Curie temperature. The PLT(10) thin film on p-doped poly-Si fabricated in this research shows excellent pyroelectric properties. The pyroelectric coefficient and the figures of merit, FV and FD at room temperature are measured as 5.76×10-4C/m2K, 1.17×10-10C.cm/J and 0.93×10-8C.cm/J, respectively.

THE TRANSPORT MECHANISM IN NANOCRYSTALLINE SILICON FILMS AT LOW TEMPERATURE

In a wide temperature range (500—20 K), we studied the electrical transport mechanism in intrinsic and P-doped nanocrystalline silicon films. We find that the HQD model successfully explains the conductivity at high temperatures (500—200K ), but fails at temperature below 200K. Single activation energy W was found in the low temperature range (100—20K), which is approximately equal to the value of kBT(W～1—3kBT).It is in good agreement with the charac teristics of hopping conduction in amorphous semiconductor, In this paper we mod ified the HQD model. We consider two distinct transport mechanisms, thermal-assi sted tunneling and electrons hopping through the local states near the Fermi lev el exist simultaneously. At high temperature tunneling transport is the main pro cess. At low temperature transport is governed by electron hopping. On this basi s, a complete analytic function of the conductivity is proposed. The function su ccessfully explains the conductivity of intrinsic and P-doped nanocrystalline si licon films in the whole temperature range.

Visible Emission from Thin-Film Phosphors of Amorphous AlN:Cu, Mn, and Cr

ABSTRACTLuminescence studies of amorphous AlN doped with Cu, Mn, or Cr were performed at 300 K. Thin films of Cu, Mn, and Cr doped amorphous AlN, ∼200 nm thick, were grown on p-doped silicon (111) substrates using RF magnetron sputtering in a nitrogen atmosphere. Cathodoluminescence (CL) showed that pure Cu doped amorphous AlN has strong emission in the blue (∼420 nm) and Mn and Cr doped films luminesce in the red (∼690 nm). Cr+3 emission is more intense than Mn+4 because chromium does not suffer from incomplete charge compensation in the III-V semiconductor. Luminescence studies of crystalline and amorphous AlN:Mn thin films showed a red shift in the emission peak by almost 100 nm and is believed to be caused by the different crystal field of the amorphous host compared to the crystalline host material. Secondary ion mass spectrometry (SIMS) depth profiling was conducted to confirm the presence of the Cu and Cr in the films and to show the amount of dopant in relation to the Si substrate.

"Ab initio" studies of hydrogen-enhanced oxygen diffusion in silicon

A novel microscopic mechanism for hydrogen-enhanced oxygen diffusion in p-doped silicon is proposed. A path for joint diffusion of O and H is obtained from an ab-initio molecular dynamics "kick" simulation. The migration pathway consists of a two-step mechanism, with a maximum energy of 1.46 eV. This path represents a 0.54 eV reduction in the static barrier when compared with the diffusion of isolated O in Si, in excellent agreement with experiments.

Role of the hot wire filament temperature on the structure and morphology of the nanocrystalline silicon p-doped films

Nanocrystalline p-doped silicon films were deposited at low substrate temperatures (around 200°C) in a hot wire reactor. In this paper we present the results on the role of the hydrogen dilution and filament temperature on the film's structure, composition, morphology and transport properties. The film's structure changes from honeycomb-like to a granular needle shape as the filament temperature changes from about 2000°C and hydrogen dilution 87%, to values above 2100°C and hydrogen dilution 90%, respectively. The nanocrystalline silicon-based films produced have optical gaps varying from 1.6 to 1.95 eV, with conductivities up to 0.2 S cm −1 and grain sizes (obtained by X-ray diffraction) in the range of 10–30 nm.

Mechanism for hydrogen-enhanced oxygen diffusion in silicon

Oxygen diffuses in silicon with an activation energy of 2.53--2.56 eV. In hydrogenated samples, this activation energy is found to decrease to 1.6--2.0 eV. In this paper, a microscopic mechanism for hydrogen-enhanced oxygen diffusion in p-doped silicon is proposed. A path for joint diffusion of O and H is obtained from an ab initio molecular-dynamics simulation in which the O atom is ``kicked'' away from its equilibrium position with a given initial kinetic energy. After reaching a maximum potential energy of 1.46 eV above the ground state, the system relaxes to a metastable state on which a Si-Si bond is broken and the H atom saturates one of the dangling bonds. With an extra 0.16 eV, the Si-H bond is broken and the system relaxes to an equivalent ground-state configuration. Therefore, the migration pathway is an intriguing two-step mechanism. This path represents a 0.54-eV reduction in the static barrier when compared with the diffusion of isolated O in Si, in excellent agreement with experiments. This mechanism elucidates the role played by the H atom in the process: it not only serves to ``open up'' a Si-Si bond to be attacked by the oxygen, but it also helps in reducing the energy of an important intermediate state in the diffusion pathway.