Silicon Schottky Barrier Research Articles

A computer-aided simulation model for the I–V characteristic of M- n- p silicon Schottky-barrier diodes produced by use of low-energy arsenic-ion implantation

Current-transport properties of Al-n-p silicon Schottky-barrier diodes have been studied both experimentally and theoretically. An analytical model for the I-V characteristic of a metal- n- p Schottky barrier diode has been developed by using an interfacial layer-thermionic-diffusion model. Assuming a Gaussian distribution for the implanted profile, the barrier-height enhancement and ideality factor have been derived analytically. Using low energy (25 KeV) arsenic implantation with the dose ranged form 8 × 10 10/cm 2 to 10 12/cm 2, Al- n- p silicon Schottky barrier diodes have been fabricated and characterized. Comparisons between the experimental measurements and the results of computer simulations have been performed and satisfactory agreements between these comparisons have been obtained. The reverse I–V characteristics of the fabricated Al- n- p silicon Schottky barrier diodes can also be well simulated by the developed model.

A theory of the admittance of an amorphous silicon Schottky barrier

A theory of the admittance of an amorphous silicon Schottky barrier

Theoretical Interpretation of Capacitance-Voltage Characteristics of Metal-a-Si:H Schottky Barriers

The capacitance-voltage characteristics of hydrogenated amorphous silicon Schottky barriers were calculated for typical cases of the gap-state density distributions in this material. It is demonstrated that the slope of a C-2 vs V plot provides the ionized state density associated with the gap-state distribution near the midgap and that the built-in potential in the barrier can be determined from the characteristic energy of gap states and the intercept voltage defined by extrapolating the straight line of the C-2 vs V plot at large reverse bias voltages.

On the mechanism of light-induced effects in hydrogenated amorphous silicon alloys

We have investigated the effects of both forward bias current soaking in the dark and prolonged light exposure on the photovoltaic properties of lightly doped, n- and p-type hydrogenated amorphous silicon Schottky barrier diodes. The results show that recombination rather than single carrier trapping is responsible for the light-induced changes.

The determination of absorption coefficients from the photo-response of silicon Schottky barriers

A novel approach to the measurement of the absorption coefficient was made through the use of differential photo-currents of Schottky barriers in order to eliminate the influence of unknown surface conditions. By varying the reverse bias on Schottky barriers created by semitransparent Au on Si wafers, the depth of the barrier layer was varied and the resulting photocurrents were used to evaluate the absorption coefficient of the substrate at room temperature. The results are in good agreement with values published in the recent literature.

An analytic model for barrier height enhancement of the Schottky barrier diode using low-energy ion implantation

This paper describes an analytic model for the barrier height enhancement of the Schottky barrier diode where the metal-np semiconductor (or metal-pn semiconductor) has been derived by considering the implanted profile of the Gaussian type in the surface-doped layer and the surface properties of the metal-semiconductor system. Experiments have also been carried out by fabricating the Al-p silicon Schottky barrier diodes with low-energy (25 keV) arsenic implantation. It is shown that the barrier height enhancement of the fabricated Schottky barrier diodes as a function of ion dose is in good agreement with the developed model.

Minority-carrier diffusion lengths in amorphous silicon-based alloys

In this paper, we present results of collection efficiency versus wavelength measurements on thick (⩾1 μm) amorphous silicon Schottky barrier photovoltaic devices illuminated through both the ohmic and Schottky contacts. These results enable us to infer the zero-field minority carrier diffusion length in amorphous silicon-based alloys by using an appropriate theoretical model. For intrinsic a-Si:H (hydrogen) films produced by the glow discharge of silane this was found to be ∼2,100 Å. Our novel approach of illuminating the devices through the ohmic contact ensures that the collection efficiency results are extremely sensitive to the minority carrier diffusion length, and we also compare this approach to surface photovoltage type experiments which we show can lead to overestimation of this quantity.

On the current-voltage characteristics of amorphous hydrogenated silicon Schottky diodes

First principle calculations of amorphous hydrogenated silicon Schottky barrier and p-i-n diodes’ current-voltage characteristics have revealed an interesting relation between the observed quality factor and the composition of the diode current. The diode current consists of two components: (1) The drift/diffusion current, JD, which is virtually independent of carrier recombination mechanism, and (2) the recombination current JR. Each component has a characteristic value of the quality factor, β (inverse slope of semilog J-V plot): β<1.1 for JD and β⩾1.6 for JR. In addition, the relative magnitudes of the two components vary with the device thickness, the density of localized states, and the surface barrier potential. The difference in the quality factors observed in Schottky barriers and in p-i-n diodes can be interpreted as an indication of change in the dominant component from JD to JR, due to a larger surface potential in the latter device.

A theory of capacitance-voltage measurements on amorphous silicon Schottky barriers

Abstract The frequency-dependent differential capacitance of an amorphous silicon Schottky barrier is calculated as a function of d.c. bias using a simple model of the Schottky barrier and an assumed form for the density of electronic states, n(E), of the silicon. The results show that at frequencies as low as 1 Hz the capacitance of the Schottky barrier can be considerably different from the static capacitance because of the slow response of the electron occupancy of localized states. A detailed development of the theory is presented to demonstrate the way in which information on n(E) is contained within the capacitance-voltage (CV) results. The deduction of n(E) from the CV results is possible if the static capacitance is known but, when relaxation effects are significant, there appears to be no simple way of obtaining n(E) directly.

Observation of two modes of current transport through phosphorus-doped amorphous hydrogenated silicon Schottky barriers

The influence of phosphorus impurities in the active layer of amorphous hydrogenated silicon Schottky barriers is investigated by experimentally studying the current-voltage characteristics of the structure and the physical and electronic properties of the material. With increasing phosphorus concentration excess diode currents develop. Numerical analysis shows that (1) these currents are due to hopping within an impurity band produced by the impurities and (2) a two-channel conduction mechanism is in quantitative agreement with the data.

Effect of hydrogen on the diode properties of reactively sputtered amorphous silicon Schottky barrier structures

The diode properties of reactively sputtered hydrogenated amorphous silicon Schottky barrier structures (a-SiHx /Pt) have been investigated. We find a systematic relation between the changes in the open circuit voltage, the barrier height, and the diode quality factor. These results are accounted for by assuming that hydrogen incorporation into the amorphous silicon network removes states from the top of the valence band and sharpens the valence-band tail. Interfacial oxide layers play a significant role in the low hydrogen content, and low band-gap regime.

Response of Schottky barrier solar cells at higher temperatures

The responses of Cu/Cr-p-type silicon and Au-n-type silicon Schottky barrier solar cells at higher temperatures have been studied. The variations of different factors, such as intrinsic carrier density, energy gap, absorption coefficient, barrier height, effective number of photons etc., have been taken into account. The results show that in the temperature range 300-450K, except for the short-circuit current, all other factors (e.g. open-circuit voltage, fill-factor and conversion efficiency) decrease with increase in temperature.

Effects of the undoped layer on characteristics of amorphous silicon Schottky diodes

The effects of undoped layer thickness on the dark and illuminated I-V characteristics of hydrogenated amorphous silicon Schottky barrier solar cells are investigated. Schottky barrier (S.B.) metals having different work function (Cr and Pd) were deposited on the 0.22 µm - 1.45 µm thick a-Si:H films. Photovoltaic performance, J sc , V oc , FF and efficiency, are independent of thickness of the undoped layer if film thickness is larger than the depletion region width. J sc and V oc are controlled by S.B. metal and FF is independent of S.B. metal. Dark I-V characteristics depend on both S.B. metal and device thickness suggesting a barrier controlled space charge limited phenomena. Variation of turn-on (threshold) voltage with undoped layer thickness can be applied to the design of switching and memory devices.

Current Transport Mechanism of Hydrogenated Amorphous Silicon Schottky Barrier Diodes

We report detailed studies on the forward current-voltage characteristics of Pd/a-Si:H Schottky barrier diodes. Exact values of the barrier height and its temperature coefficient have been determined by the internal photoemission technique. Based upon this result, the current transport mechanism through the a-Si:H Schottky barrier has been quantitatively examined. The fundamental characteristics of the Schottky barrier are considered to be dominated by diffusion theory rather than by thermionic emission theory.

An AES/XPS Study of the Chemistry of Palladium on Hydrogenated Amorphous Silicon Schottky Barrier Solar Cells

Thin layers of palladium (∼100Å thick) on hydrogenated amorphous silicon have been used as diodes and photovoltaic devices (solar cells). Auger electron spectroscopy (AES) and x‐ray photoelectron spectroscopy (XPS) in conjunction with ion‐milling were used to characterize the interface region. At the interface, a thin oxide layer is observed along with possible palladium silicides. Palladium and palladium silicides extend well into the silicon substrate. Palladium silicide is due in part to ion‐mixing. Heating device structures in caused considerable electrical degradation. Data indicate that the degradation is due to oxide formation at the Pd/a‐Si:H interface.

Image force effects on the short wavelength (UV) photoresponse of silicon Schottky barriers

An experimental study has been made of the short wavelength λ response of near-ideal silicon Schottky barrier photodetectors. It is shown that the major cause of reduced quantum efficiency (Q.E.) in this range of λ is the collection by the metal of majority carriers photogenerated within the image force maximum, in agreement with the theoretical predictions of Green. The bias-voltage dependence of the photocurrent in the near ultraviolet region is in good quantitative agreement with the image force model, with a Q.E. near unity for large reverse bias decreasing by approx. 15% at zero bias for λ = 0.37 μm, for example. The Q.E. under short-circuit conditions is relatively independent of λ for λ ≳ 0.45 μm, falling rapidly with decreasing λ from 95% at 0.45 μm to approx. 80% at 0.35 μm, again in good quantitative agreement with the above theory.

Evidence of space-charge-limited current in amorphous silicon Schottky diodes

Palladium/amorphous silicon (a-SiH x ) Schottky barrier diodes have been found to exhibit superlinear dark forward current-voltage (I-V) characteristics over the temperature range 30 to 130°C. The results are consistent with expected behavior for space-charge-limited current in the presence of distributed traps. The trap parameters are deduced from I-V data.

Photon-induced degradation in crystalline silicon Schottky barrier solar cells

Firstly a brief mention is made of the rationale behind the development of silicon Schottky barrier solar cells (SBSCs) for terrestrial photovoltaic solar energy conversion and the consequent requirement for their stability.For aluminium-thin oxide-p-type silicon SBSCs we describe a variety of photon-induced degradation effects which we observed. The effects on the illuminated and the dark current-voltage characteristics arise from changes in the interface region. Sputter Auger measurements on multilayer structures similarly produced suggest that the effects are perhaps associated with chemical bonding changes and atomic migration in the aluminium and thin oxide layers.

Interpretation of the conductance and capacitance frequency dependence of hydrogenated amorphous silicon Schottky barrier diodes

We present a general model of the frequency dependence of conductance and capacitance in a-Si:H Schottky diodes. In order to circumvent several questionable assumptions required in the analysis of capacitance voltage characteristics, the frequency dependence of sputtered a-Si:H devices is measured with no applied dc voltage. We obtain independent, consistent values of the depletion width and of the density of states at the Fermi level and below from both conductance and capacitance at both low and high modulation frequencies. We show that the linear frequency dependence of conductance cannot be attributed to hopping conductance, but rather to the interaction of gap states with free carriers. Our study shows that the interaction kinetics of the states around the Fermi level with the conduction-band carriers is so fast that the response of the diode is limited by the band transport of these carriers, which rapidly thermalize and distribute themselves through the continuum of states from the conduction band to the Fermi level.

A MESFET model for circuit analysis

A model for silicon Schottky barrier field-effect transistors (Si MESFETs) with micron and submicron dimensions has been implemented in the integrated circuit simulation program SPICE2. A description of the model and its implementation is given, together with a discussion of the physical effects that are important in submicron channel length Si MESFETs. The model is compared with d.c. experimental data with an emphasis on temperature dependence.