Interface state density in Au-nGaAs Schottky diodes

A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au-nGaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10¹⁵ and 8 × 10¹⁶ cm^?3. These diodes exhibited ideality (n) factors of approximately 1.02 and room temperature saturation current densities ～10^?8 A/cm². This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10¹³ cm^?2 eV^?1. The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.     

Effect of series resistance on the electrical characteristics and interface state energy distributions of Sn/p-Si (MS) Schottky diodes

In this study, electrical characteristics of the Sn/p-type Si (MS) Schottky diodes have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The barrier height obtained from C-V measurement is higher than obtained from I-V measurement and this discrepancy can be explained by introducing a spatial distribution of barrier heights due to barrier height inhomogeneities, which are available at the nanostructure Sn/p-Si interface. A modified Norde’s function combined with conventional forward I-V method was used to extract the parameters including barrier height (Φ_b) and the series resistance (R_S). The barrier height and series resistance obtained from Norde’s function was compared with those from Cheung functions. In addition, the interface-state density (N_SS) as a function of energy distribution (E_SS-E_V) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_b) and series resistance (R_S) for the Schottky diodes. While the interface-state density (N_SS) calculated without taking into account series resistance (R_S) has increased exponentially with bias from 4.235 × 10¹² cm⁻²eV⁻¹ in (E_SS - 0.62) eV to 2.371 × 10¹³ cm⁻²eV⁻¹ in (E_SS - 0.39) eV of p-Si, the N_SS obtained taking into account the series resistance has increased exponentially with bias from of 4.235 × 10¹² to 1.671 × 10¹³ cm⁻²eV⁻¹ in the same interval. This behaviour is attributed to the passivation of the p-doped Si surface with the presence of thin interfacial insulator layer between the metal and semiconductor.     

Inversion layer at the interface of Schottky diodes

An inversion layer can be present at the metal-semiconductor inteface of Schottky diodes with a high barrier and a lightly doped semiconductor. Its influence on the potential distribution and on the electric field distribution (especially on its maximum) is quite important and may be analyzed by means of an analytical model. The current characteristics calculated by the usual models are modified if one takes the inversion layer into account. In particular, the theoretical n of the Schottky diode is smaller than the value obtained from the usual depletion hypothesis, while the barrier height deduced from the experimental saturation current becomes larger. Excellent agreement between the experimental current characteristics of an PtSiSi diode and the combined model of thermionic emission-diffusion is obtained if the inversion layer is considered.     

Pump power calculation for parametric diodes with variable series resistance

Relations are given for the pump power lost in a parametric diode with voltage-dependent series resistance. It is shown that in the case of voltage pumping, unlike current pumping, the effective resistance for the pump power calculation is different from the average value.     

Analysis of interface states and series resistance of MIS Schottky diodes using the current-voltage (I-V) characteristics

The purpose of this paper is to analyze interface states in Al/SiO₂/p-Si (MIS) Schottky diodes and determine the effect of SiO₂ surface preparation on the interface state energy distribution. The current-voltage (I-V) characteristics of MIS Schottky diodes were measured at room temperature. From the I-V characteristics of the MIS Schottky diode, ideality factor (n) and barrier height (Φ_B) values of 1.537 and 0.763 eV, respectively, were obtained from a forward bias I-V plot. In addition, the density of interface states (N_ss) as a function of (E_ss-E_v) was extracted from the forward bias I-V measurements by taking into account both the bias dependence of the effective barrier height (Φ_e), n and R_s for the MIS Schottky diode. The diode shows non-ideal I-V behaviour with ideality factor greater than unity. In addition, the values of series resistance (R_s) were determined using Cheung’s method. The I-V characteristics confirmed that the distribution of N_ss, R_s and interfacial insulator layer are important parameters that influence the electrical characteristics of MIS Schottky diodes.     

An improved forward I-V method for nonideal Schottky diodes with high series resistance

Two methods are described to obtain the value of the series resistance(R)of a Schottky diode from its forward I-V characteristic. The value ofRis then used to plot the curve ln (I) versusV_{D} (= V - IR)which becomes a straight line even if ln(I)versusVdoes not. The ideality factornand the Schottky-barrier heightPhi_{B0}of the diode then follow from the standard procedure. The main advantages of the methods are: 1) a linear regression can be used to calculate the value ofR, 2) many data points are used over the whole data range which raises the accuracy of the results, and 3) the validity of constantRassumption can be checked by the linearity of the ln(I)versus VDcurve. The methods are illustrated on the experimental data of a real diode.     

On the temperature dependence of series resistance and interface states in Al/SiO2/p-Si (MIS) Schottky diodes

The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/w-V-T) characteristics of metal-semiconductor (Al/p-Si) Schottky diodes with thermal growth interfacial layer were investigated by considering series resistance effect in the wide temperature range (80-400 K). It is found that in the presence of series resistance, the forward bias C-V plots exhibit a peak, and experimentally shows that the peak positions shift towards higher positive voltages with increasing temperature, and the peak value of the capacitance has a maximum at 80 K. The C-V and (G/w-V) characteristics confirm that the N_ss and R_s of the diode are important parameters that strongly influence the electric parameters in (Al/SiO₂/p-Si) MIS Schottky diodes. The crossing of the G/w-V curves appears as an abnormality when seen with respect to the conventional behaviour of the ideal MS or MIS Schottky diode. It is thought that the presence of a series resistance keeps this intersection hidden and unobservable in homogeneous Schottky diodes, but it appears in the case of inhomogeneous Schottky diode. In addition, the high frequency (C_m) and conductance (G_m/w) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance.     

The role of the interface insulator layer and interface states on the current-transport mechanism of Schottky diodes in wide temperature range

In order to interpret in detail the experimentally observed current-voltage-temperature (I-V-T) and capacitance-voltage-temperature (C-V-T) results of Al/p-Si metal-semiconductor Schottky barrier diodes (SBDs) we have been examined the samples in the temperature range of 150-375 K. In the calculation method, to confirm the relationship between the I-V-T and C-V-T results, we have reported a modification which includes the ideality factor, n, and tunnelling parameter δχ^1/2 in the forward bias current characteristics. In the intermediate bias voltage region (0.1 < V < 0.6 V), the semi-logarithmic plots of the forward I-V-T curves were found to be linear. From the reverse saturation currents I₀ obtained by extrapolating the linear region of curves to zero applied voltage, the values of zero bias barrier heights ?_B0 were calculated at each temperature. The values of ideality factor calculated from the slope of each curves were plotted as a function of temperature. The values of n are 3.41-1.40 indicating that the Al/p-Si diode does obey the thermionic field emission (TFE) mechanism rather than the other transport mechanism, particularly at low temperature. The high value of ideality factors is attributed to high density of interface states in the SBDs. The temperature dependence energy density distribution profile of interface state was obtained from the forward bias I-V-T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density N_ss decreasing with increasing temperature was interpreted by the result of atomic restructuring and reordering at the metal-semiconductor interface. After the modification was made to the forward current expression, we obtained a good agreement between the values of barrier height obtained from both methods over a wide temperature.     

The analysis of the electrical characteristics and interface state densities of Re/n-type Si Schottky barrier diodes at room temperature

The main electrical characteristics of current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature of the Re/n-type Si Schottky barrier diodes prepared by pulsed laser deposition (PLD) method have been examined. The values of the basic electrical properties such as forward saturation current (I_o), ideality factors (n), barrier heights (Ф_bo), rectification ratio (RR) and series resistances (R_S) were obtained from I-V and C-V measurements using different calculation methods. At low voltages (V ≤ 0.3 V), the electrical conduction was formed to take place by thermionic emission, whereas at high voltages (V > 0.3 V), a space charge limited conduction mechanism was shown. Furthermore, the interface state densities (N_SS) as a function of energy distribution (E_SS- E_V) was obtained from the I-V data by taking into account the bias dependence of the effective barrier height (Φ_b) for the Re/n-type Si Schottky barrier diodes.     

Measurement of series resistance in IMPATT diodes

A new method is given for determining the electrical series resistance of an IMPATT diode. The measurement is based on observation of the oscillation threshold bias current for a diode in a standard circuit. The method is applied to GaAs diodes near 40 GHz. The values obtained are used to quantitatively explain other performance characteristics of the diodes.     

Flicker noise by random walk of electrons at the interface in nonideal Schottky diodes

An explanation of low frequency 1/f noise in nonideal Schottky barrier diodes is presented where the current fluctuation is attributed to the random walk of electrons at the metal-semiconductor interface via modulation of the barrier height. The experimental results on TiN/n-Si Schottky diodes have been successfully analysed to give useful information on the interface states.     

Study the effect of distribution of density of states on the depletion width of organic Schottky contacts

Organic semiconductor to metal Schottky contacts have been widely used in electronic devices and to investigate the properties of organic semiconductors. In designing and characterizing these devices the full depletion approximation is used. The analytical and numerical simulations presented in this paper suggest that this approximation is not generally valid. Simulations of a Schottky contact between regioregular-poly 3 hexylthiophene (rr-P3HT) and aluminum show that this approximation becomes worse as molecular order decreases, with the potential profile increasingly deviating from the expected quadratic function of position. Also the depletion width decreasing well below that predicted using the approximation. In this work the slope of the band tail is used as a measure of disorder.     

Current-voltage characteristics of Schottky barrier diodes withdynamic interfacial defect state occupancy

Schottky barrier diode theory conventionally assumes that the barrier height remains constant with the applied bias. However, high ideality factors and certain anomalous capacitance-voltage characteristics can only be explained by letting the barrier height vary with the applied voltage. Changes in the occupation of surface states have been inferred to be the cause of this change in barrier height, although the precise nature of these surface states has not yet been determined. This article examines the role of monoenergetic interfacial defect states whose occupancy is dynamically controlled by the local carrier densities, rather than by equilibrium conditions. Certain types of surface donor and acceptor states are shown to have a strong influence on the resulting current-voltage characteristics. The Al/GaAs(100) system is discussed in detail and experimental results are compared to this analytic model     

The effect of an interfacial layer on minority carrier injection in forward-biased silicon Schottky diodes

It is shown that the degree of minority carrier injection in Au-Si junctions can be substantially increased by the inclusion of a thin interfacial layer between the metal and the semiconductor. When a forward voltage is applied to the junction, a part of this voltage is developed across the interfacial layer. This favours the reduction of the barrier height to minority carriers, which tunnel from the metal into the semiconductor. The minority carrier injection current increases at the expense of the majority carrier current.For a given oxide thickness, γ(= J_minority/J_tot) increases with forward bias, approaching a saturation value for a few volts applied to the junction. For a given voltage, γ also shows a variation with interfacial layer thickness, δ, and the present results indicate that an oxide thickness can be chosen to optimise γ. In the case of a gold-silicon junction with an insulating layer of thermally-grown oxide, as δ is increased to 40 Å, the saturation value of γ increased from $\text{10}{}^{\mathrm{?4}}\text{for δ = 10}\text{A}\text{?}$ through a maximum of 2 × 10^?1 for δ ? 30 Å. For oxides prepared by r.f. sputtering, the maximum value of γ is 10^?1 and occurs for δ ? 80 Å.These results are of considerable importance in the improvement of injection luminescence in metal-semiconductor diodes.     

The breakdown voltage of planar Schottky diodes

The breakdown-voltage-limiting edge effects of Schottky diodes are analysed, with special emphasis on the planar Schottky-diode structure. The numerical two-dimensional calculation of the field distribution in this structure shows that the breakdown voltage can be increased by appropriate design ; the breakdown voltage cannot, however, reach its bulk value because it is limited by and dependent on the shape of the oxide cut resulting from the photolithographic processes. Computer-calculated normalized plots are given which can be used in the design of planar Schottky diodes.     

The effect of Ti:W barrier metal on characteristics of palladium-silicide Schottky barrier diodes

The values of diode-quality factor and reverse-current leakage of Au/Pd/Ti:W/Pd₂Si/nSi unguarded Schottky barrier diodes are much higher than expected from silicide/silicon junction-radius induced highfield effects. Experimental Ti-, W-, and Ti:W-MIS structures were built and tested to show that Ti is responsible for the formation of a parasitic Ti-MIS structure around the unguarded-diode perimeter. This parasitic structure is responsible for excessive current leakage and also for an additional unguarded-diode degradation induced by annealing at 400 °C.     

The performance of Schottky diodes as far-infrared modulators

We analyze the performance as a terahertz-frequency modulator of a small-area Schottky diode mounted in a corner-cube antenna. The analysis includes the effects of carrier inertia and dielectric relaxation as modeled by Champlin and Eisenstein (1978). It also includes the effect of the vanishing of the depletion region above the flat-band potential, as modeled by Crowe and Mattauch (1986). Our baseline calculation refers to a 1.4 μm diameter diode (Univ. of Virginia batch no. 1E12) operated at a carrier frequency of 2.52 THz and a modulation frequency of 8 GHz, as was used in the experiments of Watson, Grossman, and Phillips (1988). The effects on reflectivity modulation, and therefore on sideband-generation efficiency, of varying the diode parameters are investigated. Our conclusions are: A) For all realistic diode parameters, the phase modulation completely dominates the amplitude modulation. B) Performance is degraded well below the plasma frequency in the undepleted epilayer due to the presence of a second resonance, caused by the interaction of the barrier capacitance and the effective inductance due to carrier inertia, C) The effects of varying the antenna impedance, temperature, diode substrate size, and Schottky barrier height over realistic ranges are small. D) An improvement in single-sideband conversion efficiency of approximately 20 db may be obtained by increasing the epilayer doping and simultaneously reducing the diode radius.     

The origins of leaky characteristics of Schottky diodes on p-GaN

The possible origins of the leaky characteristics of a Schottky barrier on p-GaN have been investigated. The as-grown samples did not show any electrical activity using Hall measurements. Ni diodes made on as-activated samples, either at 950/spl deg/C for 5 s or at 750/spl deg/C for 5 min exhibited quasiohmic behavior. Upon sequential etching of the sample to remove a surface layer of 150 /spl Aring/, 1200 /spl Aring/, and 5000 /spl Aring/ from the sample, the I-V behavior became rectifying. I-V-T measurements showed that the slopes of the lnI-V curves were independent of the temperature, indicative of a prominent component of carrier tunneling across the Schottky junction. C-V measurements at each etch-depth indicated a decreasing acceptor concentration from the surface. The highly doped (>1.7 /spl times/ 10/sup 19/ cm/sup -3/) and defective surface region (within the top 150 /spl Aring/ from surface) rendered the as-activated Schottky diodes quasiohmic in their I-V characteristics. The leaky I-V characteristics, often reported in the literature, were likely to originated from the surface layer, which gives rise to carrier tunneling across the Schottky barrier. This highly doped/defective surface region, however, can play an important role in ohmic contact formation on p-GaN.