Si Schottky Barrier Research Articles

Kinetics of formation and properties of epitaxial CoSi2 films on Si (111)

Very thin CoSi2 films, epitaxially grown on silicon (111) surfaces, have been obtained under ultrahigh vacuum conditions by thermal reaction of Co layers deposited onto Si (111) substrates. The morphology and structural properties of the CoSi2 films depend strongly on experimental parameters such as film thickness, annealing temperature to form CoSi2, or substrate temperature during Co deposition. Usually for high-temperature formation (≥700 °C) and large thickness (≥200 Å) CoSi2 islands are observed. Below these limits the CoSi2 films display a rather smooth and homogeneous aspect. The reaction kinetics are also followed in situ monitoring the Co and Si Auger peaks versus annealing temperature. Two interfaces have been examined, namely Co–Si and Co–CoSi2. Plateaus in the Auger peak variation show the evolution of the sampled region from the Co metallic phase to successively Co2Si, CoSi, and CoSi2 phases. Finally, electrical characteristics of some nearly perfect CoSi2–Si Schottky barriers have been checked with intensity and capacitance versus voltage techniques. The deduced barrier ranges around 0.65±0.02 eV and no signal has been detected with deep-level transient spectroscopy.

Effects of interface structure on the electrical characteristics of PtSi-Si Schottky barrier contacts

The properties of PtSiSi Schottky barrier contacts formed by a new technique employing multilayer metallization are compared with those of contacts prepared by the conventional single-layer metallization method. The multilayer technique permits the formation of very shallow contacts without any limitation being placed on the thickness of the PtSi layer. For a PtSi layer of given thickness the PtSi-Si contact interface obtained by this technique is more uniform than the interface formed by annealing a single layer of platinum on silicon. The interfacial uniformity is independent of PtSi thickness for shallow PtSiSi contacts produced by the multilayer technique, while for conventional contacts the uniformity decreases with increasing PtSi thickness. Large-area (9.4 × 10 -3 cm 2) diodes utilizing shallow PtSiSi contacts about 200 Å deep have been fabricated without guard rings. These diodes exhibit near-ideal forward current-voltage characteristics, low reverse leakage currents (less than 5 nA at -10 V) and high breakdown voltages (over -90 V). These characteristics are superior to those of diodes using conventional PtSi-Si contacts.

Model for Localized States Distribution and Light Dependent Effects in Amorphous Silicon Solar Cells

The localized state density for amorphous Si (a·Si) can be reasonably approximated by a U-shaped hyperbolic function for the theoretical analysis of the potential profile in the depletion layer of a·Si Schottky barrier solar cells. The photocurrent dependence on the width of the depletion layer has been theoretically analyzed with emphasis on the effect of minority carrier recombination in the depletion layer and the shrinkage of the depletion width under sunlight due to hole trapping. The detailed analysis shows that the minority carrier diffusion length Lp is about 0.15 µm and the optimum width of the undoped layer in Schottky barrier solar cells is in the range of 0.2–0.44 µm for the minimum density of gap states of 1017–1016 cm-3eV-1, respectively.

Photoelectron injection at metal-semiconductor interfaces

A modelling of the photoinjection process is developed which permits fitting of the spectral photoresponse of Schottky barriers including the electric field dependence of barrier height and photoresponse by means of two adjustable parameters: the zero field barrier qφ BO and λ 0 the zero temperature mean free path for optical phonon scattering of high energy electrons. The model assumes an image force potential barrier with Thomas-Fermi screening in the metal. Effects of optical phonon scattering and quantum mechanical transmission are convoluted on the Fowler photoelectron supply function. The effects of phonon scattering are frequently large because the ranges in energies associated with the transverse momentum and normal momentum are approximately the amount by which the quantum energy hv exceeds the barrier energy qφ B. At high fields, quantum mechanical tunneling dominates the response when hv < qφ B. At low fields, phonon assisted transmission is appreciable for the same quantum energy range. The calculation of the collection probability includes effects of multiple scattering even for electrons that do not lie initially within the cone of acceptance at the barrier maximum. An approach that considers the probability of collection the same as that of reaching the potential maximum without scattering is found to be acceptable only at high fields. Experimental results are reported from oxide-passivated epitaxial Pt x Si-〈111〉 n-type Si Schottky barrier diodes with annular Schottky barrier guard rings measured at temperatures of 90 and 298 K for an electric field range from 5 × 10 3 to 9 × 10 4 V cm . The field, spectral and temperature dependences of the photoresponse data are in excellent agreement with theoretical predictions with λ 0 = 110 Å at both 90 and 298 K. The zero field barrier height obtained from fitting photoresponse curves at a number of electric fields is also in excellent agreement with I-V and C-V measurements.

Influence of preparation conditions on forward-bias currents of amorphous silicon Schottky diodes

We report on the open-circuit voltage Voc and the forward-current–voltage characteristic, J=Js(expqV/nKT−1), of Schottky diodes obtained by evaporation of platinum onto hydrogenated amorphous silicon (a-Si :H) fabricated by glow-discharge decomposition of silane. The diode characteristics were studied as a function of several preparation parameters, namely, silane pressure, substrate temperature, silane flow rate, annealing temperature. Rectifying behavior was obtained only for substrate temperatures between 200 and 300°C. Within this constraint, the preparation parameters have only a small effect on Voc but have large influences on n and Js. The factor n decreases towards ideality (n=1) as the silane pressure decreases, as the substrate temperature increases and with annealing of the Pt contact. The corresponding decrease of the concentration of polyhydride H sites with similar variations in the preparation parameters suggests that the recombination center responsible for nonideal value of n are associated with the polyhydride sites. We argue that the nearly constant value of Voc and therefore of the potential barrier probably originates from the crossing of the Fermi level with deep levels near the interface rather than from a previously proposed interface state. Although we were unable to use a sufficiently low temperature to choose between the thermionic emission and diffusion theories for the forward-current-voltage relationship, we point out that carrier injection in the metal base transistor structure favors a thermionic emission model. Assuming thermionic emission the value deduced for the Richardson constant is of the same order of magnitude as found for crystal Si Schottky barriers.

Efficiency calculations for thin-film polycrystalline semiconductor Schottky barrier solar cells

Numerical calculations have been made of the effect of grain size on the short-circuit current and the AM1 efficiency of polycrystalline thin film InP, GaAs, and Si Schottky barrier solar cells. Si cells 10 µm thick are at best 8 percent efficient for 100-µm grain sizes; 25-µm-thick Si cells can be about 10 percent efficient for this grain size. GaAs cells 2 µm thick can be 12 percent efficient for grain sizes of 3 µm or greater.

Frequency-Conductance Characteristic of the Sputtered Mo-n Si Schottky Barrier

We have studied the frequency-conductance characteristics of the sputtered Mo-n Si Schottky barrier by using an AC small signal equivalent network. As a result, it was found that a damaged layer is formed on the Si surface and a deep level in the damaged layer acts as a trapping center for electrons. The deep level in the damaged layer is localized in the vicinity of the mid band gap and the capture cross-section is of the order of 10-12 cm2. The damaged layer was annealed at a temperature of 500°C and a level like the continuous surface level is left at the Mo–Si interface.The capture cross-section of this level is of the order of 10-16 cm2.

Behavior of various silicon Schottky barrier diodes under heat treatment

Variations of Schottky forward voltage with heat treatment have been observed for AlPd 2Si Si and Si-doped AlPd 2Si Si Schottky barrier diodes. These variations have been reduced to a minimum by the use of a barrier metal such as TiW between Al and the silicided contacts.

An Integrated Photodetector Using the Partially Metal-Clad-Dielectric-Slab Waveguide Structure

A hybrid-type integrated photodetector which uses metal-semiconductor Schottky barrier diode incorporated in the partially metal-clad-dielectric-slab waveguide (PMC line) structure is proposed, analysed and experimentally studied. The PMC line serves not only as electrodes but also as a two-dimensionally confining structure for a guided optical wave. The wave is coupled from the PMC line into the depletion layer of the diode through a coupling layer and a thin metal film; this scheme avoids the reflection loss inherent to conventional detectors. The analysis indicates that the present photodetector using Si-Schottky barrier diode can be designed so that the quantum efficiency of 92% and cut-off frequency of 6.1 GHz are obtainable at 0.63 µm wavelength.

Fabrication of ZnSi Schottky barrier diode by controlling the substrate temperature during evaporation

Fabrication of ZnSi Schottky barrier diode by controlling the substrate temperature during evaporation

Capacitive effects of Au and Cu impurity levels in Pt- N type Si Schottky barriers

Au and Cu impurity effects on the capacitance-voltage ( C– V) relationship of Pt- n type Si Schottky barrier diodes have been investigated over the frequency range of 100 Hz to 500 kHz at 200°K and 300°K. The barrier height of the Pt-Si system measured by C– V, I– V, and photothreshold techniques was 0.83±0.01 eV. Deep level C– V effects previously predicted by Roberts and Crowell were observed. Diodes on phosphorus-doped Si nearly compensated with Au clearly exhibited a non-monotonic low frequency C– V relationship. An inflection point in the C −2- V curve attributable to the Au donor level 0.77 eV from the conduction band edge was observed. The experimental data show that the presence of deep levels makes barrier height measurements appreciably ambiguous and that impurity profiles determined from a C– V relationship using a model which neglects their presence can be shifted appreciably both in apparent magnitude and apparent position.

Behavior of AlSi Schottky barrier diodes under heat treatment

Behavior of AlSi Schottky barrier diodes under heat treatment

Integrated 6-GHz receiver front-end circuits for a radio relay system

A 6-GHz integrated front end was made using microwave integrated circuits and satisfying system specifications. The front end consists of a mixer and a local oscillator made from a 1.5-GHz phase-locked loop and a frequency quadrupler. A noise figure better than 6 dB was achieved using Si Schottky barrier diodes.

Hafnium-Silicon Schottky Barriers: Large Barrier Height on p-Type Silicon and Ohmic Behavior on n-Type Silicon

Schottky-barrier diodes of Hf on p-type Si gave a height φMS = 0.90 eV, which is the largest value of φMS reported to date on Schottky barriers on either p- or n-type Si. Excellent agreement was found between the φMS values determined from current-voltage, activation energy, and capacitance-voltage analyses. This large value of φMS of the Hf-(p)-Si Schottky barrier allows several new applications which were not possible before in the integrated circuit technology, such as clamping of p-n-p transistors and fabrication of enhancement-mode p-channel Schottky gate field-effect transistors. Hafnium deposited on n-type Si (ND≅5×1015 cm−3) gave Ohmic behavior suggesting the validity of the work-function-difference model for the Hf–Si system. Under this assumption, the Schottky-barrier analysis gives the work function of Hf=4.23±0.02 eV.

THERMIONIC-FIELD RESISTANCE MAXIMA IN METAL-SEMICONDUCTOR (SCHOTTKY) BARRIERS

A maximum in the differential resistance versus applied bias relationship of metal-semiconductor contacts is predicted to occur when current flow is predominantly by thermionic-field (thermally excited tunnel) emission. The predicted resistance peaks are generally asymmetrical with respect to voltage and may occur on either side of zero bias. The peak location has only an indirect correlation with the Fermi kinetic energy in the semiconductor. The theoretical approach is generally applicable to any metal-semiconductor system when the dominant carrier flux is associated with the tail of a Fermi-Dirac distribution. The theory is in reasonable agreement with recent experimental resistance measurements on Cr–Si Schottky barrier diodes at 77°K.

FORWARD CURRENT-VOLTAGE CHARACTERISTICS AND DIFFERENTIAL RESISTANCE PEAK OF A SCHOTTKY BARRIER DIODE ON HEAVILY DOPED SILICON

An analysis of the forward current-voltage data for a temperature range of 77.2° to 423°K on a Cr–Si (ND = 7 × 1018 cm−3) Schottky barrier diode is given. The I-V behavior of such a diode, which obviously does not follow the simple Schottky theory, is not explained by the more recent calculations of Padovani and Stratton, and of Crowell and Rideout in which field emission is taken into account. It is observed that the peak in differential resistance and its variation with voltage on such a diode is in reasonable agreement with the theories of Stratton and Padovani, and of Crowell and Rideout.

Conduction properties of the Au-n-type—Si Schottky barrier

Although the theory of the metal-semiconductor Schottky barrier is some twenty years old, it has received little experimental verification. In the present work, diodes consisting of evaporated gold on n-type silicon surfaces have been fabricated. Reproducibility of diode characteristics (± 10 mV at a given forward current) was obtained by suitable chemical treatments of the surfaces. These diodes have been studied with the major emphasis on the current-voltage characteristics as a function of the doping level of the silicon and temperature.For temperatures greater than 0°C and for Si resistivity above 1 ω-cm, the forward current, in the range studied (< 1 A/cm2), increases exponentially with voltage, the slope being very nearly q/kT (within 10 per cent) as predicted by the simple diode theory. At lower Si resistivities, an excess current component appears, which may be accounted for by space-charge recombination. Indeed, at temperatures below −40°C, the slope is close to q/2kT. From the temperature dependence of the reverse current the recombination-generation centers have been located at 0·31 eV from the center of the band gap.The reverse current is dominated by the excess current component at room temperatures and below. The variation with voltage of high-temperature reverse current can be accounted for by the Schottky effect (effective barrier lowering due to electron-image force).The barrier heights determined from the forward and reverse characteristics are consistent with each other, and also in good agreement with those obtained from capacitance-voltage and photoelectric measurements. The diodes fabricated on 0·1 to 10 ω-cm Si may be characterized by a zero-field barrier height of 0·79 ± 0·02 eV, and a Richardson constant in the range of 10–70 A/cm2 °C2.