Anomalous current transport in Au/low-doped n-GaAs Schottky barrier diodes at low temperatures

0 effect, the zero-bias barrier height was found to exhibit two different trends in the temperature ranges of 77–160 K and 160–300 K. The variation in the flat-band barrier height with temperature was found to be -(4.7±0.2)×10⁴ eVK^-1, approximately equal to that of the energy band gap. The value of the Richardson constant, A^**, was found to be 0.27 A cm^-2K^-2 after considering the temperature dependence of the barrier height. The estimated value of this constant suggested the possibility of an interfacial oxide between the metal and the semiconductor. Investigations suggested the possibility of a thermionic field-emission-dominated current transport with a higher characteristic energy than that predicted by the theory. The observed variation in the zero-bias barrier height and the ideality factor could be explained in terms of barrier height inhomogenities in the Schottky diode. Received: 4 December 1997/Accepted: 28 July 1998     

Current transport mechanism in Al/Si3N4/p-Si (MIS) Schottky barrier diodes at low temperatures

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-insulator-semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80-300 K. By using the thermionic emission (TE) theory, the zero-bias barrier height Φ_B0 calculated from I-V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C-V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a Φ_B0 versus q/2kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ_Bo = 0.826 eV and α_o = 0.091 V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln(I_o/T²) − q²σ_o²/2(kT)² versus q/kT plot gives Φ_B0 and Richardson constant A^* as 0.820 eV and 30.273 A/cm² K², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm² K² is very close to the theoretical value of 32 A/cm² K² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/Si₃N₄/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density (N_SS) profiles was determined from the forward I-V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.     

Current conduction mechanism in Al/p-Si Schottky barrier diodes with native insulator layer at low temperatures

The forward bias current-voltage (I-V) characteristics of Al/p-Si (MS) Schottky diodes with native insulator layer were measured in the temperature range of 80-300 K. The obtained zero bias barrier height Φ_B0(I-V), ideality factor (n) and series resistance (R_s) determined by using thermionic emission (TE) mechanism show strong temperature dependence. There is a linear correlation between the Φ_B0(I-V) and n because of the inhomogeneties in the barrier heights (BHs). Calculated values from temperature dependent I-V data reveal an unusual behaviour such that the Φ_B0 decreases, as the n and R_s values are increasing with decreasing absolute temperature, and these changes are more pronounced especially at low temperatures. Such temperature dependence of BH is contradictory with the reported negative temperature coefficient of the barrier height. In order to explain this behaviour we have reported a modification in the expression reverse saturation current I_o including the n and the tunnelling factor (αΧ^1/2δ) estimated to be 15.5. Therefore, corrected effective barrier height Φ_bef.(I-V) versus temperature has a negative temperature coefficients (α = −2.66 × 10⁻⁴ eV/K) and it is in good agreement with negative temperature coefficients (α = −4.73 × 10⁻⁴ eV/K) of Si band gap. In addition, the temperature dependent energy distribution of interface states density N_ss profiles was obtained from the forward bias I-V measurements by taking into account the bias dependence of the Φ_e and n. The forward bias I-V characteristics confirm that the distribution of N_ss, R_s and interfacial insulator layer are important parameters that the current conduction mechanism of MS Schottky diodes.     

Electron transport and barrier inhomogeneities in palladium silicide Schottky diodes

+ silicon wafer held at 573 K, are measured over a temperature range 37–307 K and analyzed in terms of thermionic emission–diffusion (TED) theory by incorporating the concept of barrier inhomogeneities through a Gaussian distribution function. The process adopted is shown to yield an ideal Schottky diode with a near constant barrier height of 0.734 V and ideality factor 1.05 in the temperature interval 215–307 K. Below 215 K, both the barrier height (φ_bo) and the ideality factor (η) exhibit abnormal temperature dependence and are explained by invoking two sets of Gaussian distributions of barrier heights at 84–215 K and 37–84 K. Further, it is demonstrated that the forward bias makes the Gaussian distribution dynamic so that the mean fluctuates (i.e., increases or decreases depending on whether its voltage coefficient is positive or negative) and the standard deviation decreases progressively, i.e., the barrier homogenizes temporarily. The changes occur in such a way that the apparent barrier height at any bias is always higher than at zero-bias. Finally, it is pointed out that the presence of single/multiple distributions can be ascertained and the values of respective parameters deduced from the φ_ap vs. 1/T plot itself. Also, the inverse ideality factor versus inverse temperature plot provides bias coefficients of the mean barrier height and standard deviation of the distribution function. Received: 6 January 1997/Accepted: 29 April 1997     

Correlation between barrier heights and ideality factors of Cd/n-Si and Cd/p-Si Schottky barrier diodes

Our goal is to experimentally investigate whether or not the effective Schottky barrier heights (SBHs) and ideality factors obtained from the current-voltage (I-V) and capacitance-voltage (C-V) characteristics differ from diode to diode even if the samples were identically prepared. For this purpose, we prepared Cd/n-Si (33 dots) and Cd/p-Si (15 dots) diodes. The SBH for the Cd/n-Si diodes ranged from 0.701 to 0.605 eV, and ideality factor n from 1.913 to 1.213. Φ_b value for the Cd/p-Si diodes ranged from 0.688 to 0.730 eV, and ideality factor n value from 1.473 to 1.040. The experimental SBH distributions obtained from the C⁻²-V and I-V characteristics were fitted by a Gaussian function and their mean SBH values were calculated. Furthermore, the laterally homogeneous barrier heights were also computed from the extrapolation of the linear plot of experimental barrier heights versus ideality factors.     

Analysis of current-voltage characteristics of inhomogeneous Schottky diodes at low temperatures

Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current-voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current-voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current-voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.     

The barrier height inhomogeneity in Al/p-Si Schottky barrier diodes with native insulator layer

The current-voltage (I-V) characteristics of Al/p-Si Schottky barrier diodes (SBDs) with native insulator layer were measured in the temperature range of 150-375 K. The estimated zero-bias barrier height Φ_B0 and the ideality factor n assuming thermionic emission (TE) theory show strong temperature dependence. Evaluation of the forward I-V data reveals an increase of zero-bias barrier height Φ_B0 but decrease of ideality factor n with increase in temperature. The conventional Richardson plot exhibits non-linearity below 250 K with the linear portion corresponding to activation energy of 0.41 eV and Richardson constant (A^*) value of 1.3 × 10⁻⁴ A cm⁻² K⁻² is determined from intercept at the ordinate of this experimental plot, which is much lower than the known value of 32 A cm² K² for holes in p-type Si. Such behavior is attributed to Schottky barrier inhomogene ties by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Also, Φ_B0 versus q/2kT plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of Φ_B0 = 1.055 eV and σ₀ = 0.13 V for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Thus, the modified versus q/kT plot gives Φ_B0 and A^* as 1.050 eV and 40.08 A cm⁻² K⁻², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 40.03 A cm⁻² K⁻² is very close to the theoretical value of 32 A K⁻² cm⁻² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/p-Si Schottky barrier diodes with native insulator layer can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights.     

Tunneling current-voltage characteristics of Ti-silicide/p− Si/p+ Si Schottky diodes

The tunneling current-voltage characteristics of Ti-silicide/p^– Si/p⁺ Si Schottky diodes are analyzed to study the Ti/Si interface properties. By using an MBE-grown 7 nm p^– Si spacer layer, well-defined tunneling structures are obtained. The sharply peaked density of states in a Ga-impurity band is used as a tunneling probe. A state density gap 100 meV around the Fermi energy is observed for a rapidly (20s) annealed (T=550°C) reacted sample. The gap is interpreted by a Ti-rich interfacial silicide film of about 1 nm.     

The effect of series resistance on capacitance-voltage characteristics of Schottky barrier diodes

The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the Ti/p-Si Schottky barrier diodes (SBDs) have been investigated taking into account the effect of the interface states and series resistance of the device. The forward C-V measurements have been carried out in the range frequency of 0.3-2 MHz (at six different frequencies). It is seen that the forward C-V plots exhibit anomalous peaks in the presence of a series resistance. It has been experimentally determined that the peak positions in the C-V plot shift towards lower voltages and the peak value of the capacitance decreases with increasing frequency. In addition to, the effect of series resistance on the capacitance is found appreciable at higher frequencies due to the capacitance decreases with increasing frequency.     

Electrical Characteristics of Co/n-Si Schottky Barrier Diodes Using I-V and C-V Measurements

Electrical characteristics of Co/n-Si Schottky barrier diodes are analysed by current- voltage （I- V） and capacitancevoltage （C- V） techniques at room temperature. The electronic parameters such as ideality factor, barrier height and average series resistance are determined. The barrier height 0. 76 eV obtained from the C - V measurements is higher than that of the value 0. 70 eV obtained from the I - V measurements. The series resistance Rs and the ideality factor n are determined from the d ln（ I） /dV plot and are found to be 193.62 Ω and 1.34, respectively. The barrier height and the Rs value are calculated from the H（I） - I plot and are found to be 0.71 eV and 205.95Ω. Furthermore, the energy distribution of the interface state density is determined from the forward bias I - V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density Nss ranges from 6.484×10^11 cm^-2eV^-1 in （Ec - 0.446） eV to 2.801×10^10 cm^-2eV^-1 in （Ec - 0.631） eV, of the Co/n-Si Schottky barrier diode. The results show the presence of a thin interracial layer between the metal and the semiconductor.     

Determination of the laterally homogeneous barrier height of thermally annealed and unannealed Au/p-InP/Zn-Au Schottky barrier diodes

We have identically prepared Au/p-InP Schottky barrier diodes (SBDs). The diodes were annealed up to 400 °C thermally. The barrier height (BH) for the as-deposited Au/p-InP/Zn-Au SBDs from the current-voltage characteristics have varied from 0.58 to 0.72 eV, and ideality factor n from 1.14 to 1.47. The BH for the annealed SBDs from the current-voltage characteristics have varied from 0.76 to 0.82 eV, and ideality factor n from 1.17 to 1.39. As a result of the thermal annealing, it has been seen that the BH values of the annealed SBDs are larger than those of the as-deposited SBDs. We have determined a lateral homogeneous BH value of 0.72 eV for the as-deposited Au/p-InP SBD from the experimental linear relationship between barrier heights and ideality factors, and a value of 0.85 eV for the annealed Au/p-InP SBD. The increase of 0.13 eV in the BH value by means of 400 °C annealing has been ascribed to the formation of the excess charges that electrically actives on the semiconductor surface.     

Barrier-height non-uniformities of PtSi/Si(111) Schottky diodes

The forward current-voltage characteristics of PtSi Schottky contacts on epitaxial n-type Si (111) is studied in the temperature range from 100 to 300 K. A current contribution in excess to that predicted by thermionic emission diffusion theory is caused by a few thousand patches of reduced Schottky barrier height in a device area of 3.14 mm². The typical lateral extent of these patches is 70–250 nm. It correlates with the size of surface bumps observed. The number of patches is reduced upon increasing the silicidation temperature up toT _siI=550°C. Possible non-uniformities of the typical crystallite grain size of 20 nm are not resolved due to effective pinch-off.     

The effect of interface states, excess capacitance and series resistance in the Al/SiO2/p-Si Schottky diodes

The current-voltage (I-V) characteristics of Al/SiO₂/p-Si metal-insulator-semiconductor (MIS) Schottky diodes were measured at room temperature. In addition the capacitance-voltage (C-V) and conductance-voltage (G-V) measurements are studied at frequency range of 10 kHz-1 MHz. The higher value of ideality factor of 3.25 was attributed to the presence of an interfacial insulator layer between metal and semiconductor and the high density of interface states localized at Si/SiO₂ interface. The density of interface states (N_ss) distribution profile as a function of (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_e) at room temperature for the Schottky diode on the order of ≅4 × 10¹³ eV⁻¹ cm⁻²_. These high values of N_ss were responsible for the non-ideal behaviour of I-V and C-V characteristics. Frequency dispersion in C-V and G-V can be interpreted only in terms of interface states. The N_ss can follow the ac signal especially at low frequencies and yield an excess capacitance. Experimental results show that the I-V, C-V and G-V characteristics of SD are affected not only in N_ss but also in series resistance (R_s), and the location of N_ss and R_s has a significant on electrical characteristics of Schottky diodes.     

Schottky barrier and pn-junctionI/V plots — Small signal evaluation

This paper proposes and examines three different plots for the determination of the saturation current, the ideality factor, and the series resistance of Schottky diodes and solar cells from the measurement of a single current (I)/voltage(V) curve. All three plots utilize the small signal conductance and avoid the traditional Norde plot completely. A test reveals that the series resistance and the barrier height of a test diode can be determined with an accuracy of better than 1%. Finally it is shown that a numerical agreement between measured and fittedI/V curves is generally insufficient to prove the physical validity of current transport models.     

Intersecting behaviour of nanoscale Schottky diodes I-V curves

We describe a new feature connected with Schottky barriers with nanosize dimensions. We found out by theoretical analysis that the I-V curves of such small diodes measured at different temperatures should intersect and consecutively at higher voltages larger current flows through the diode at lower temperatures. This effect which is at first glance in contradiction with the thermionic theory is caused by the series resistance influence. We show that the presence of the series resistance is a necessary condition of its observation. However, the intersection voltage—minimum voltage at which the intersection may occur—increases with the value of the series resistance and the diode dimensions for which the effect could be observable in Si diodes and the common series resistance values must be in submicrometer range. Diodes with several hundreds nanometers dimension have the intersection voltage ∼1 V. Analytical expression for the intersection voltage values was also derived.     

Carrier recombination and high-barrier Schottky diodes on silicon

Small-area high-barrier Schottky diodes have a very high dynamic resistance. Consequently, special care is needed when measuring the current-voltage characteristic of such diodes. The reported observation of carrier recombination in the depletion layer of high-barrier IrSi/Si Schottky diodes at room temperature is shown to be due to instrumental loading of the diodes. Careful measurements show that carrier recombination is observed only below 200 K and is dependent on the dimension of the diode.     

Numerical analysis of gate leakage current in AlGaN Schottky diodes

We studied theoretically the influence of the tunneling current on the leakage current in AlGaN Schottky diodes. It is shown that the most important conductance mechanism in these structures is the tunneling. The thermionic emission has lower influence on the total current practically throughout the whole reverse bias range and doping concentrations studied. For high doping concentrations we found very slow temperature dependence of the diode current.     

Inhomogeneities in 130 MeV Au ion irradiated Au/n-Si (1 0 0) Schottky structure

The electrical characteristics of Au/n-Si (1 0 0) Schottky rectifier have been studied in a wide irradiation fluence range using conventional current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V characteristics showed an abnormal increase in forward current at low voltage. The device shows a bend in forward I-V and reverses bias C-V characteristics due to extra current, suggesting that there are two independent contributions to thermionic current, corresponding to two levels of the Schottky barrier. It is shown that the excess current at low voltage can be explained by taking into account the role of heavy ion irradiation induced defects at the metal semiconductor interface.     

Photovoltaic characteristics of Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) at various temperatures

The charge conduction properties of the Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) were investigated using current–voltage–temperature (I–V–T) measurements in dark and under various illumination levels. For this purpose, the main diode parameters such as reverse-saturation current (I_o), zero-bias barrier height (Φ_Bo), ideality factor (n), series resistance (R_s) and shunt resistance (R_sh) of diode were obtained as function of temperature and illumination level. Experimental results show that all of these electrical parameters are strong functions of illumination and temperature. The change in all electrical parameters becomes more important at low temperatures and illumination levels. While the n value decreases with increasing temperature and illumination level, Φ_Bo value increases. The fill factor (FF = V_m·I_m/V_oc·I_sc) values were obtained as 0.34 at 80 K and 0.40 at 320 K under 50 W and these values are near to a photodiode. Therefore, the fabricated diode can be used as a photodiode in optoelectronic applications. The forward bias I–V characteristics of the diode have also been explained by the space charge limited current (SCLC) model.     

Temperature-dependent optical absorption measurements and Schottky contact behavior in layered semiconductor n-type InSe(:Sn)

The layered n-InSe(:Sn) single crystal samples have been cleaved from a large crystal ingot grown from non-stoichiometric melt by the Bridgman-Stockbarger method. It has been made the absorption measurements of these samples without Schottky contact under electric fields of 0.0 and 6000 V cm⁻¹. The band gap energy value of the InSe:Sn has been calculated as 1.36 ± 0.01 eV (at 10 K) and 1.28 ± 0.01 eV (at 300 K) under zero electrical field, and 1.31 ± 0.01 eV (at 10 K) and 1.26 ± 0.01 eV (at 300 K) under 6000 Vcm⁻¹. The current-voltage (I-V) characteristics of Au-Ge/InSe(:Sn)/In Schottky diodes have been measured in the temperature range 80-320 K with a temperature step of 20 K. An experimental barrier height (BH) Φ_ap value of about 0.70 ± 0.01 eV was obtained for the Au-Ge/InSe(:Sn)/In Schottky diode at the room temperature (300 K). An abnormal decrease in the experimental BH Φ_b and an increase in the ideality factor n with a decrease in temperature have been explained by the barrier inhomogeneities at the metal-semiconductor interface. From the temperature-dependent I-V characteristics of the Au-Ge/InSe(:Sn)/In contact, that is, and A^* as 0.94 ± 0.02 and 0.58 ± 0.02 eV, and 27 ± 2 and 21 ± 1 (A/cm² K²), respectively, have been calculated from a modified versus 1/T plot for the two temperature regions. The Richardson constant values are about two times larger than the known value of 14.4 (A/cm² K²) known for n-type InSe. Moreover, in the temperature range 80-320 K, we have also discussed whether or not the current through the junction has been connected with TFE.