Semsettin Altindal

Investigation of Electrical Characteristics in Al/CdS-PVA/p-Si (MPS) Structures Using Impedance Spectroscopy Method

The cadmium sulfide (CdS) nanopowders have been prepared by ball-milling method, and CdS-polyvinyl alcohol (PVA) nanocompound in the form of film has been deposited on a p-Si wafer as an interfacial layer by spin-coating method. The impedance characteristics of the fabricated Al/CdS-PVA/ p-Si (metal-polymer-semiconductor)-type structures were studied in the frequency and voltage range of 5 kHz-5 MHz and ±1 V, respectively, by considering interface states (D_it), series resistance (R_s), and interfacial layer effects at 300 K. While the voltage and frequency dependence profiles of D_it were evaluated from the low-high frequency capacitance (C_LF-C_HF) and Hill-Coleman methods, R_s profiles were evaluated from the Nicollian and Brews method. Doping concentration atoms (N_A) and barrier height [Φ_B(capacitance-voltage (C-V))] values were also obtained from the reverse bias C-2 versus V plots for each frequency. While D_it and R_s values decrease with increasing frequency almost exponentially, Φ_B(C-V) increases linearly. Therefore, both the measured capacitance (C_m) and conductance (G_m/w) values were corrected to eliminate the R_s effect. The experimental results show that R_s value is more effective on the impedance measurements at high frequencies in the accumulation region, but D_it is effective at low frequencies in the depletion region.

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}

In this paper, an Al-TiW-Pd₂ Si/n-Si Schottky diode with an area of 6 × 10^-6 cm² was fabricated using the photolithographic technique. The electrical and dielectric properties of the TiW-Pd₂Si/n-Si structure have been studied in detail by using experimental capacitance-voltage-temperature (<i>C</i>-<i>V</i> -<i>T</i>) and conductance-voltage-temperature (<i>G</i>/<i>w</i>-<i>V</i> -<i>T</i>) characteristics in the temperature range of 300-400 K comparing at two frequencies. It has been found that the forward-bias <i>C</i>-<i>V</i>- <i>T</i> and <i>G</i>/<i>w</i> -<i>V</i>-<i>T</i> plots exhibit a peak at 50 kHz, particularly at high temperatures. However, the peaks of <i>C</i>-<i>V</i> -<i>T</i> and <i>G</i>/<i>w</i> -<i>T</i> plots seen clearly at low frequency tend to disappear at 500 kHz, at which only the free carriers within the majority bands are able to respond to the small excitation alternating-current signal. The effect of the series resistance <i>Rs</i> of TiW-Pd₂Si/n-Si structures on the abnormal behaviors of <i>C</i>- <i>V</i>-<i>T</i> and <i>G</i>/<i>w</i>-<i>V</i> -<i>T</i> profiles was investigated. It was found that <i>Rs</i> decreases with increasing temperature at the range of 310-360 K. The dielectric properties were found to be a strong function of temperature at two frequencies. The results indicate that the interfacial polarization can be more easily occurred at 50 kHz and high temperatures.

Structures in Wide Frequency Range

Electrical and interfacial properties of ITO/PEDOT:PSS/poly((9,9-dioctylfluorene)-2,7-diyl(2-dodecyl-benzo[1,2,3]triazole)) (PFTBT)/Au devices were investigated using current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/w-V) measurements at room temperature. The forward and reverse C-V and G/w-V measurements were carried out in the frequency range of 10 kHz-1MHz. The electrical parameters, barrier height (ΦBo ) and ideality factor (n) obtained from the forward bias LnI-V plot were found as 0.711 eV and 3.8, respectively. In addition, the series resistance (Rs ) was obtained using Norde and Cheungs methods; Rs were found as 19.052kΩ and 19.267kΩ, respectively. The experimental C-V and G/w-V characteristics of these structures at various gate biases show fairly large frequency dispersion especially at low frequencies and applied voltage due to interface states (Nss) in equilibrium with the conjugated copolymer, interfacial polymer and Rs . These observations indicate that at low frequencies, the charges at interface states can easily follow an AC signal and yield an excess capacitance and conductance. On the other hand, the values of Nss were determined using high-low frequency capacitance (CLF -CHF ) method and Nss are of order 1011 eV-1 cm−2 which is closer to the values obtained by Hill-Coleman method. Experimental results show that both Nss and Rs values should be taken into account in determining frequency and voltage dependent I-V, C-V and G/w-V characteristics for an organic structure.