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.
Pure polyvinyl alcohol (PVA) capped ZnS semiconductor nanocrystals were prepared by microwave-assisted method, and the optical and structural properties of the as-prepared materials were ...characterized by x-ray diffraction (XRD) and Ultraviolet–visible (UV-Vis) techniques. The XRD pattern shows the formation of ZnS nanocrystals, and the UV–Vis spectroscopy results show a blue shift of about 1.2 eV in its band gap due to the confinement of very small nanostructures. The concentration of donor atoms (
N
D
), diffusion potential (
V
D
), Fermi energy level (
E
F
), and barrier height (Φ
B
(
C
–
V
)) values were obtained from the reverse bias
C
−2
–
V
plots for each frequency. The voltage dependent profile of series resistance (
R
s
) and surface states (
N
ss
) were also obtained using admittance and low–high frequency methods, respectively.
R
s
–
V
and
N
ss
–
V
plots both have distinctive peaks in the depletion region due to the spatial distribution charge at the surface states. The effect of
R
s
and interfacial layer on the
C
–
V
and
G
/
ω
–
V
characteristics was found remarkable at high frequencies. Therefore, the high frequency
C
–
V
and
G
/
ω
–
V plots
were corrected to eliminate the effect of
R
s
. The real and imaginary parts of dielectric constant (
ε
′ and
ε
″) and electric modulus (
M
′ and
M
″), loss tangent (tan
δ
), and ac electrical conductivity (
σ
ac
) were also obtained using
C
and
G
/
ω
data and it was found that these parameters are indeed strong functions of frequency and applied bias voltage. Experimental results confirmed that the
N
ss
,
R
s
, and interfacial layer of the MPS structure are important parameters that strongly influence both the electrical and dielectric properties. The low values of
N
ss
(~10
9
eV
−1
cm
−2
) and the value of dielectric constant (
ε
′ = 1.3) of ZnS-PVA interfacial layer even at 10 kHz are very suitable for electronic devices when compared with the SiO
2
. These results confirmed that the ZnS-PVA considerably improves the performance of Au/n-Si (MS) structure and also allow it to work as a capacitor, which stores electric charges or energy.
In this study, we have purposed to combine both polystyrene (PS) and 3,4-ethylenedioxythiophene (EDOT) groups as a gate dielectric and to fabricate a transparent organic field effect transistor ...(OFET) device with polymeric gate electrode using this novel organic dielectric material. The focus point of this work is to obtain a transparent OFET and to minimize the interface states between gate insulator and gate electrode. Firstly, we have synthesized EDOT functional polystyrene (PS-EDOT) copolymer as gate insulator via “click” chemistry between azide-functional styrene copolymer and propargyl-functionalized EDOT. We used the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) conductive polymer mixture as a suitable alternative gate electrode instead of inorganic contacts, which is a new topic in the organic electronics. The contact resistance value was measured as 1/600 (S/cm)
-1
. At the end of the process transparent OFETs with different channel length were fabricated using spin coating method by which poly(3-hexylthiophene) (P3HT), novel PS-EDOT copolymer insulator and PEDOT:PSS were coated on prepatterned OFET substrate. Electrical characterizations of OFET devices were held in total darkness and in air ambient in order to achieve output and transfer current-voltage (
I
-
V
) characteristics. The main parameters such as the threshold voltage (
V
Th
), field effect mobility (
μFET
) and current on/off ratio (
I
on
/
off
) of the devices were extracted from capacitance-frequency (
C
-
f
) plot. It was found that fabricated PS-EDOT OFETs exhibit good device performances such as low
V
Th
, remarkable mobility, and
I
on
/
off
values.
Au/PPy/n-Si (MPS) type Schottky barrier diodes (SBDs) were produced and their current–voltage (
I–V)
characteristics were measured in the positive and negative bias regions at 300 K. The basic ...electronic quantities such as reverse-saturation current (
I
o
), ideality factor (
n
), zero-bias barrier height (
Ф
B0
), series (
R
s
)
and shunt resistances (
R
sh
) were obtained by using
I–V
data in total darkness and illumination (100 W/m
2
). The values of these parameters were found as 7.79 × 10
−9
A, 5.41, 0.75 eV, 1 kΩ and 130 MΩ in dark) and 4 × 10
−9
A, 4.89, 0.77 eV, 0.9 kΩ and 1.02 MΩ under illumination), respectively. Also the energy density distribution behaviors of surface states (
N
ss
) have been acquired by calculation of effective barrier height (
Ф
e
) and ideality factor
n (V)
depending on voltage in total darkness and illumination. The values of
N
ss
show an exponentially increase from the mid-gap of Si to the lower part of conduction band (
E
c
) for two conditions. The possible current conduction mechanisms were determined by plotting of the double logarithmic
I–V
plots in the positive voltage zone and the value of current was found proportional to voltage (
I∼V
m
). The high values of
n
and
R
s
were ascribed to the certain density distribution of
N
ss
localized at semiconductor/PPy interface, surface conditions, barrier inequality, the thickness of PPy interlayer and its roughness. The open-circuit voltage of the photodiode was found as 0.36 V under 100 W/m
2
illumination level. This is evidence that the fabricated sample is very sensitive to illumination. Therefore, it can be put into practice in optoelectronic industries as a photodiode or solar cells.
The dielectric properties of Au/PPy/n-Si metal-polymer-semiconductor (MPS)-type Schottky barrier diodes (SBDs) were investigated by using capacitance-voltage (
C-V
) and conductancevoltage (
G/ω-V
) ...measurements at various temperatures and voltages at frequencies of 100 kHz and 500 kHz. Both the real and the imaginary parts of the complex dielectric constant and dielectric loss (
ε
′,
ε
″) and of the electric modulus (
M
′,
M
″), as well as the conductivity (σ
ac
), were found to depend strongly on the temperature and the voltage. Both the
C
and
G/ω
values increased with increasing applied voltage and had inversion, depletion, and accumulation regions as with a metal-insulator-semiconductor (MIS) type behavior. Both the dielectric constant (
ε′
) and the dielectric loss (
ε
″) increased with increasing temperature and decreased with increasing frequency. The loss tangent (tan
δ
)
vs
. temperature curve had a peak at about 200 K for both frequencies. The
M
′ and the
M
″ values decreased with increasing temperature and became independent of the frequency at high temperatures. The series resistance (
R
s
) of the diode decreased with increasing temperature for the two frequencies while the σ
ac
increased. Such behaviors of the dielectric properties with temperature were attributed to the restructuring and reordering of charges at interface states/traps due to the varying temperature, the interfacial polarization, and the interfacial polymer layer. ln(σ
ac
)
vs
. q/kT plots had two distinct linear regions with different slopes for the two frequencies. Such behaviors of these plots confirmed the existence of two different conduction mechanisms corresponding to low and high temperatures. The values of the activation energy (
E
a
) were obtained from the slopes of these plots, and its value at low temperatures was considerably lower than that at high temperatures.
In this study, (CuO doped PVA) composite material was deposited using spin coating technique on n-Si and the Au/CuO-PVA/n-Si Metal/Polymer/Semiconductor type Schottky Barrier Diodes (MPS type SBDs) ...were fabricated. The electrical measurements of Au/CuO-PVA/n-Si SBDs were realized in the dark and under various UV (365 nm) light intensities ranging from 50 to 250 mW/cm2. The basic parameters of the MPS type SBDs such as leakage current (I0), zero bias barrier height (ΦB0), barrier height (ΦB), ideality factor (n), series resistance (Rs), shunt resistance (Rsh), rectification rate (RR), photocurrent (Ipc) and surface states (Nss) were obtained Current-Voltage (I–V) plot based on Thermionic Emission (TE) theory, and Norde function depending on the UV light intensity. As the light intensity increases, RR, Rsh, ΦB0, and ΦB decreased but the n and I0 increased. In addition, the increase of UV light intensity caused the increase of photocurrent in MPS type SBDs and thus MPS type SBDs exhibited more ohmic behavior.
In the present study, cadmium sulphide (CdS) nanopowders were prepared by using a simple physical ball milling technique, and their x-ray diffraction (XRD) analysis confirmed the formation of ...hexagonal wurtzite structure of CdS. The morphology of CdS nanopowders was characterized by scanning electron microscope (SEM). Dielectric and electrical properties of the manufactured Al/(CdS-PVA)/p-Si (MPS) type structures were investigated by capacitance–voltage (
C
–
V
) and conductance–voltage (
G
/
ω
–
V
) measurements as functions of temperature and applied bias voltage at 500 kHz. Some main parameters of the structure such as real and imaginary parts of complex dielectric constants,
ε′
(=
ε′
–
jε″
), loss tangent (tan
δ
), a.c. electrical conductivity (
σ
ac
), and real and imaginary parts of complex electric modulus,
M*
(=
M′
+
jM″
) of the structure were investigated in the temperature range between 230 K and 340 K. Ln(
σ
ac
)–
q
/
kT
curve showed a linear behavior. The value of activation energy (
E
a
) was obtained as 0.0601 eV at 5.0 V from the slope of this curve. Moreover, argand diagrams of complex modulus were studied to determine relaxation process of these structures.
•The Al/(CdS-PVA)/P-Si (MPS) structures were prepared using the ball milling technique.•The frequency and voltage dependent of electrical and dielectric properties were obtained using C-V and G/ω-V ...dates.•Real and imaginary permittivity (ε' and ε''), dissipation factor (tanδ), ac electrical conduction mechanism (σac), real and imaginary part of electric modulus (M' and M'') were obtained at frequency between 5kHz - 5MHz and at voltage between (-1V) - (+1V).
In this study, the effect of frequency and voltage on the dielectric properties of Al/(CdS-PVA)/p-Si structures prepared using cadmium sulfide (CdS)-polivinyl alcohol (PVA) interface material was investigated. For this purpose, real and imaginary permittivity (ε' and ε''), dissipation factor (tanδ), ac electrical conduction mechanism (σac), real and imaginary part of electric modulus (M' and M'') were obtained by using capacitance-conductance (C-G/ω) measurements at frequency between 5kHz - 5MHz and at voltage between (-1V) - (+1V). All parameters were found to depend considerably on the frequency and voltage. ε' and ε'' reach higher values at low frequencies due to surface states (Nss) which can easily monitor ac signal, dipolar polarization and interfacial polarization. Short-range mobility of charge carriers caused the increase of both electrical modulus and σac with increasing frequency. Moreover, M'' exhibited a peak behavior which shifts to higher frequency with increasing voltage. Peak behavior could be ascribed to both decrease in polarization and surface states.
In order to improve and detailedly investigate the dielectric properties of polymer interfaces of Metal–Polymer–Semiconductor (MPS) structures, three types of MPS were fabricated by doping 1, 3 and ...5% graphene (Gr) into the polyvinyl alcohol (PVA) interface material. Capacitance–Voltage (
C-V
) and Conductance–Voltage (
G/ω-V
) measurements were used to analyze the dielectric properties of three types of MPS. Using
C-V
and G/ω-V data, series resistance (
R
s
) affecting device performance and interface properties besides basic dielectric parameters of each structure such as both the real and imaginary components of complex dielectric constant (
ε'
and
ε''
), complex electrical modulus (M' and M''), loss tangent (tanδ), and ac electrical conductivity (
σ
ac
) were also calculated. The effect of graphene doping was examined for each parameter and obtained results were compared at both low (0.1 MHz) and high (1 MHz) frequencies. It was observed that ε and ε'' decreased with increasing graphene doping at both 0.1 and 1 MHz, while M' and M'' increased under same conditions. Moreover, both the M' and M'' vs V plots have two distinctive peaks between −2.0 V and 0.0 V due to a special density distribution of surface states between (Gr-PVA) and p-Si. The tanδ gradually increased with increasing graphene doping at only 0.1 MHz. As the doping ratio of graphene increases, the charge carriers in the structure generate more dipoles and create an earlier relaxation process. In other words, increasing the doping ratio helps to improve the series resistance effects in MPS structures. As a result, it was seen that the interfacial properties of MPS structures were improved by increasing the rate of graphene doping.
