A. Kaya

Capacitance/Conductance–Voltage–Frequency Characteristics of

The energy dependence of the interface states (N_ss) and relaxation time (τ) and capture cross section (σp) of N_ss in (Au/PVC+TCNQ/p-Si) heterojunction were investigated using high-low frequency capacitance (C_HF-C_LF) and conductance method, which contains many capacitance/conductance [C/(G/ω)-V] plots. The C value of the heterojunction increases with decreasing frequency as almost exponentially due to the existence of N_ss between metal and semiconductor. The N_ss and τ values have been obtained in the (0.053- E_v)-(0.785- E_v)-eV energy range by considering the voltage-dependent surface potential obtained from the lowest measurable frequency C-V curve at 1 kHz. The magnitude of N_ss ranges from 3.88×10¹² eV^-1cm^-2 to 3.24×10¹² eV^-1cm^-2. In the same energy range, the value of τ ranges from 5.73×10^-5 to 1.58×10^-4 s and shows almost an exponential increase with increasing bias from the top of the valence band edge toward the midgap of semiconductor. The obtained N_ss values from C_HF-C_LF and conductance methods are in good agreement with each other for the heterojunction. As a result, the mean value of N_ss was found on the order of 10¹² eV^-1cm^-2 and this value is very suitable for an electronic device.

{\rm Au}/{\rm PVC}+{\rm TCNQ}/{\rm p}\hbox{-}{\rm Si}

The dielectric properties, electric modulus and ac electrical conductivity (σac) of Al/Co-doped (PVC+TCNQ)/p-Si structures have been investigated in the wide frequency and voltage range of 0.5 kHz–3 MHz and (-4 V)–(9 V), respectively, using the capacitance-voltage (C–V) and conductance-voltage (G/ω–V) measurements at room temperature. The real and imaginary parts of dielectric constant (e′, e″), loss tangent (tan δ), σac and the real and imaginary parts of electric modulus (M′, M″) were found strongly function of frequency and applied voltage especially at low frequencies. The e′–V plot shows an anomalous peak in the forward bias region due to the series resistance (Rs), surface states (Nss) and interfacial layer (PVC+TCNQ) effects for each frequency and then it goes to negative values known as negative dielectric constant (NDC) at low frequencies (f ≤ 70 kHz). Such observation of NDC is important result because it implies that an increment of bias voltage produces a decrease in the charge on the electrodes. The amount of negativity e′ value increases with decreasing frequency and this decrement in the NDC corresponds to the increment in the e″.

Structures in Wide Frequency Range

In order to compare the main electrical parameters such as ideality factor (n), barrier height (BH) (ΦI–V), series (Rs) and shunt (Rsh) resistances and energy density distribution profile of surface states (Nss), the Au/n-Si (MS) Schotthy diodes (SDs), with and without interfacial (Ca1.9Pr0.1Co4Ox) layer were obtained from the current–voltage (I–V) measurements at room temperature. The other few electrical parameters such as Fermi energy level (EF), BH (ΦC–V), Rs and voltage dependence of Nss profile were also obtained from the capacitance–voltage (C–V) measurements. The voltage dependence of Nss profile has two distinctive peaks in the depletion region for two diodes and they were attributed to a particular distribution of Nss located at metal–semiconductor (MS) interface. All of these results have been investigated at room temperature and results have been compared with each other. Experimental results confirmed that interfacial (Ca1.9Pr0.1Co4Ox) layer enhanced diode performance in terms of rectifier rate (RR=IF/IR at ±3.4 V), Nss (at 0.5 eV) and Rsh ( − 3.4 V) with values of 265, 5.38 × 1013eV−1⋅cm−2 and 7.87 × 104Ω for MS type Schottky barrier diode and 2.56 × 106, 1.15 × 1013 eV−1⋅cm−2 and 7.50 × 108Ω for metal–insulator–semiconductor (MIS) type SBD, respectively. It is clear that the rectifying ratio of MIS type SBD is about 9660 times greater than MS type SBD. The value of barrier height (BH) obtained from C–V data is higher than the forward bias I–V data and it was attributed to the nature of measurements. These results confirmed that the interfacial (Ca1.9Pr0.1Co4Ox) layer has considerably improved the performance of SD.

On the frequency dependent negative dielectric constant behavior in Al/Co-doped (PVC+TCNQ)/p-Si structures

The barrier height (BH) of the Au/(Ca1.9Pr0.1Co4Ox)/n-Si structure was evaluated in the temperature range of 120–360 K using current–voltage (I–V) measurements. The zero-bias BH (ΦBo) and ideality factor (n) values deduced from standard thermionic emission theory were found to be 0.35 eV and 6.30 at 120 K and 0.83 eV and 5.1 at 360 K, respectively. Because such changes in ΦBo were not in agreement with the negative temperature coefficient (α) of the Si band gap, effects of tunnelling and BH inhomogeneity were added to the analysis of junction current. With this modification, the value of ΦBef. was found to decrease with temperature at a rate of −2.4 × 10−4 eVK−1 in approximate agreement with the known α of the Si band gap. Attempts to model the inhomogeneous BH with a single Gaussian distribution were also successful, rendering a mean value of BH () of 0.997 eV and a standard deviation (σo) of 0.12 eV. Similar conclusions were drawn from additional analyses, employing the modified Richardson plots. Our results suggest that the analysis of electronic transport at this and possibly other MIS junctions should include both the effect of tunnelling and that of BH inhomogeneity.

A comparative study on the electrical parameters of Au/n-Si Schottky diodes with and without interfacial (Ca1.9Pr0.1Co4Ox) layer

Current transport mechanisms (CTMs) of Au/Ca3Co4Ga0.001Ox/n-Si/Au (MIS) type structures were investigated using current–voltage (I–V) characteristics in the temperature range of 80–340 K. Semilogarithmic I–V plots show two linear regions corresponding to low (0.075–0.250 V) and moderate (0.27–0.70 V) biases, respectively. Zero-bias barrier height (ΦB0) was observed to increase with increase in the temperature, whereas opposite behaviour was observed for ideality factor (n). ΦB0 and (n−1–1) vesus q/2kT and ΦB0 versus n plots were drawn to get an evidence of Gaussian distribution (GD) of the barrier heights. These plots, too, show two linear regions corresponding to low (80–160 K) and high (200–340 K) temperature ranges (LTR and HTR), respectively. Mean value of barrier height (B0) and standard deviation (σs) were extracted from the intercept and slope of ΦB0 versus q/2kT plots for two linear regions as 0.382 eV, 0.0060 V for LTR and 0.850 eV, 0.135 V for HTR at low biases and 0.364 eV, 0.0059 V for LTR and 0.806 eV, 0.132 V for HTR at high biases, respectively. B0 and Richardson constant (A*) values were also obtained from the intercept and slope of the modified Richardson (Ln(Io/T2)−(q2σs2/2k2T2) versus q/kT) plots as 131.81 Acm−2 K−2, 0.381 eV for LTR and 129.35 Acm−2 K−2, 0. 854 eV for HTR at low biases and 148.01 Acm−2 K−2, 0.377 eV for LTR and 143.77 Acm−2 K−2, 0.812 eV for HTR at high biases, respectively. In conclusion, CTM in the structure can be successfully explained in terms of thermionic emission theory with the double GD of barrier heights.

Electronic transport of Au/(Ca1.9Pr0.1Co4Ox)/n-Si structures analysed over a wide temperature range

The temperature and voltage dependence profile of the surface states (Nss), series resistance (Rs) and electrical conductivity (σac) have been investigated in temperature and voltage ranges of 140–400 K and (-5 V)-(6 V), respectively. The value of barrier height (BH) decreases with increasing temperature as ΦB(T) = (1.02 - 4×10-4⋅T) eV. These values of negative temperature coefficient (-4×10-4eV⋅K-1) is in good agreement with the α of band gap of SiC (-3.1×10-4 eV⋅K-1). Capacitance-voltage (C–V) plots for all temperatures show an anomalous peak in the accumulation region because of the effect of series resistance (Rs) and Nss. The effect of Rs and Nss on the C and conductance (G) are found noticeable high especially at low temperatures. The decrease in C values also corresponds to an increase in G/ω values in the accumulation region. In addition, Ln(σac) versus q/kT plots have two straight lines with different slopes which are corresponding to below and above room temperatures for various forward biases which are an evident two valid possible conduction mechanisms. The values of activation energy (Ea) were obtained from the slope of these plots and they changed from 6.3 meV to 4.7 meV below room temperatures and 42.5 meV to 34.4 meV for above room temperatures, respectively.

On double exponential forward bias current-voltage (I–V) characteristics of Au/Ca3Co4Ga0.001Ox/n-Si/Au (MIS) type structures in temperature range of 80–340 K

The forward and reverse bias current–voltage (I–V) characteristics of Au/V-doped polyvinyl chloride+Tetracyanoquino dimethane/porous silicon (PVC+TCNQ/p-Si) structures have been investigated in the temperature range of 160–340 K. The zero bias or apparent barrier height (BH) (Φap = ΦBo) and ideality factor (nap = n) were found strongly temperature dependent and the value of nap decreases, while the Φap increases with the increasing temperature. Also, the Φap versus T plot shows almost a straight line which has positive temperature coefficient and it is not in agreement with the negative temperature coefficient of ideal diode or forbidden bandgap of Si (αSi = -4.73×10-4eV/K). The high value of n cannot be explained only with respect to interfacial insulator layer and interface traps. In order to explain such behavior of Φap and nap with temperature, Φap Versus q/2kT plot was drawn and the mean value of (ΦBo) and standard deviation (σs) values found from the slope and intercept of this plot as 1.176 eV and 0.152 V, respectively. Thus, the modified (ln(Io/T2)-(qσs)2/2(kT)2 versus (q/kT) plot gives the ΦBo and effective Richardson constant A* as 1.115 eV and 31.94 A⋅(cm⋅K)-2, respectively. This value of A*( = 31.94 A⋅(cm⋅K)-2) is very close to the theoretical value of 32 A⋅(cm⋅K)-2 for p-Si. Therefore, the forward bias I–V–T characteristics confirmed that the current-transport mechanism (CTM) in Au/V-doped PVC+TCNQ/p-Si structures can be successfully explained in terms of the thermionic emission (TE) mechanism with a Gaussian distribution (GD) of BHs at around mean BH.