Subhash Chand

Current-voltage characteristics and barrier parameters of Pd2Si/p-Si(111) Schottky diodes in a wide temperature range

Current-voltage characteristics of Pd2Si/p-Si(111) Schottky barrier diodes studied over a wide temperature range (60-201 K) are shown to follow a thermionic emission-diffusion mechanism under both the forward and the reverse bias conditions. The barrier parameters as evaluated from the forward I-V data reveal a decrease of zero-bias barrier height ( phi b0) but an increase of ideality factor ( eta ) and series resistance (Rs) with decrease in temperature. Moreover, the changes in phi b0, eta and Rs become quite significant below ~100 K. An In(Is/T2) versus 1/T plot is found to fit well with two straight lines in different temperatures regimes giving an activation energy of 0.33 eV (201-107 K) and 0.24 eV (below 107 K) and an effective Richardson constant of 33 A cm-2 K-2. However, the activation energy of 0.33 eV corresponds to the zero-bias barrier height at absolute zero. An In(Isf/T2) versus 1/ eta T plot is suggested to obtain the flat-band barrier height and the effective Richardson constant; the corresponding values obtained are 0.401 eV and 32.2 A cm-2 K-2 respectively. It is shown that the `T0 effect` cannot account for the apparent increase in ideality factor and decrease of barrier height at low temperatures. Finally, the decrease of barrier height with voltage under the reverse bias condition is attributed mainly to interfacial layer effects with a small contribution due to image force lowering.

Evidence for the double distribution of barrier heights in Schottky diodes from I - V - T measurements

The current - voltage (I - V) characteristics of palladium silicide-based Schottky diodes on n-type silicon have been measured over a wide temperature range (66 - 300 K). Their analysis on the basis of the thermionic emission - diffusion (TED) mechanism reveals an abnormal decrease of zero-bias barrier height and increase of ideality factor with decrease in temperature (T) and nonlinearity in the activation energy plot. Such behaviour is attributed to barrier inhomogeneities by assuming a Gaussian distribution of barrier heights at the silicide/silicon interface. Evidence is given for the existence of a double Gaussian distribution having mean barrier heights of 0.79 V and 0.64 V and standard deviations of 0.081 V and 0.057 V with ideality factors 1.064 and 1.363, and remain effective in the temperature range 134 - 300 K and 66 - 120 K respectively. Further, the effect of forward bias on the distribution parameters is discussed. A simple method, involving the use of a zero-bias barrier height versus inverse temperature plot, is suggested to deduce the presence of single/multiple distribution(s) of barrier heights and to determine the respective parameters.

On the existence of a distribution of barrier heights in Pd2Si/Si Schottky diodes

The current–voltage characteristics of Pd2Si based Schottky diodes on both n‐ and p‐type silicon measured over a wide temperature range (52–295 K) have been interpreted on the basis of thermionic emission‐diffusion mechanism and the assumption of a Gaussian distribution of barrier heights. It is shown that while the occurrence of a distribution of barrier heights is responsible for the apparent decrease of the zero‐bias barrier height (φb0) and nonlinearity in the activation energy plot, the voltage dependence of the standard deviation causes the unusual increase of ideality factor (η) at low temperatures. Also, it is demonstrated that the forward bias shifts the mean barrier height towards the higher side and causes narrowing of the distribution as well. A simple method, involving the use of φb0 vs 1/T data, is suggested to gather evidence for the occurrence of a Gaussian distribution of barrier heights and obtain values of mean barrier height and standard deviation. The experimental results correspond t...

Effects of barrier height distribution on the behavior of a Schottky diode

The current–voltage characteristics of a Schottky diode are simulated numerically using the thermionic emission-diffusion mechanism and considering a Gaussian distribution of barrier heights, with a linear bias dependence of both the mean and standard deviation. The resulting data are analyzed to get insight into the effects of distribution parameters on the barrier height, activation energy plots and the ideality factor over a temperature range 50–300 K. It is shown that with a Gaussian distribution of the barrier heights the system continues to behave like a single Schottky diode of apparently low zero-bias barrier height and a high ideality factor. Its barrier height decreases, activation energy plot becomes non-linear and ideality factor increases with a decrease in temperature. While the distribution parameters are responsible for the abnormal decrease of barrier height, their bias dependences account for the higher ideality factor at low temperatures. Also, the pivotal role played by series resistan...

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

The forward current-voltage (I–V) characteristics of Pd2Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height (ϕb0) and an increase of the ideality factor (η) with decreasing temperature. Further, the changes in ϕb0 and η become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and “T0-effect” fail to account for the temperature dependence of the barrier parameters. The 1n(Is/T2) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd2Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 104 A m−2 K−2 against the theoretical value of 1.12 × 106 A m−2 K−2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.

On the intersecting behaviour of current?voltage characteristics of inhomogeneous Schottky diodes at low temperatures

This paper explains the phenomenon of intersection of current–voltage (I–V) curves observed recently in inhomogeneous Schottky diodes at low temperatures, generated using an analytical equation. The crossing of the ln(I)–V curves appears as an abnormality when seen with respect to the conventional behaviour of ideal Schottky diodes. Here it is shown that this crossing of ln(I)–V curves is an inherent property of any Schottky diode. For a homogeneous Schottky diode, it can be observed by plotting ln(I)–V curves with zero series resistance at various temperatures. It is the presence of series resistance that keeps this intersection hidden and unobservable in homogeneous Schottky diodes. In inhomogeneous Schottky diodes with Gaussian distribution of barrier heights, this crossing is observable in the usual range of ln(I)–V curves at low temperatures even with finite (non-zero) series resistance. The analytical model of the Gaussian distribution of barrier heights thus favours crossing. However, the calculations based on the numerical integration method do not show such intersection. The detailed aspects of this intersecting behaviour of ln(I)–V curves in inhomogeneous Schottky diodes are discussed in this paper.

An accurate approach for analysing an inhomogeneous Schottky diode with a Gaussian distribution of barrier heights

An unexpected observation in the current–voltage curves of Schottky diodes, containing barrier inhomogeneities generated using the analytical results based on a Gaussian distribution model of barrier heights is reported. Calculations based on these results show that, at very low temperatures, Schottky diodes exhibit higher currents than at higher temperatures. This is an unusual observation, indicating a high current through the Schottky diodes at lower temperatures, which is inconsistent with the thermionic emission diffusion theory. The effects causing this unusual behaviour are explored by analysing a conventional model. A more accurate approach is presented which explains this unusual behaviour and yields results consistent with the theoretical behaviour of the Schottky diodes.

Simulation and analysis of the I - V characteristics of a Schottky diode containing barrier inhomogeneities

The current - voltage (I - V) characteristics of Schottky diodes containing barrier inhomogeneities have been simulated using thermionic emission - diffusion (TED) theory and assuming a Gaussian distribution of barrier heights. The system is considered to have a number of non-interacting parallel diodes with each corresponding to a different barrier height within the distribution limit. The mean and the standard deviation of the Gaussian distribution are taken either as constant or having linear bias dependences. The simulated I - V data are then analysed to study the effects of the distribution parameters and their bias coefficients on the barrier height and the ideality factor over a temperature range of 50 - 300 K. It is shown that the mere existence of a distribution causes a decrease in the zero-bias barrier height and, in turn, leads to nonlinearity in the activation energy plots. Also, the decrease is greater for high values of standard deviation. Further, the abnormal increase of ideality factor with decrease in temperature occurs due to the bias dependence of the standard deviation of the distribution. Finally, it is demonstrated that the decrease in temperature and increase in standard deviation cause similar effects and both lead to a decrease in barrier height and an increase in ideality factor. Also, the role of the series resistance in adversely influencing the linearity of the log(I) - V characteristics of a Schottky diode containing barrier inhomogeneities is discussed.