Electronic properties of Al/DNA/p-Si MIS diode: Application as temperature sensor

The current-voltage (I-V) measurements were performed in the temperature range (200-300 K) on Al/DNA/p-Si Schottky barrier type diodes. The Schottky diode shows non-ideal I-V behaviour with ideality factors n equal to 1.34 ± 0.02 and 1.70 ± 0.02 at 300 K and 200 K, respectively, and is thought to have a metal-interface layer-semiconductor (MIS) configuration. The zero-bias barrier height Φ_b determined from the I-V measurements was 0.75 ± 0.01 eV at 300 K and decreases to 0.61 ± 0.01 eV at 200 K. The forward voltage-temperature (V_F-T) characteristics were obtained from the I-V measurements in the temperature range 200-300 K at different activation currents (I_F) in the range 20 nA-6 μA. The V_F-T characteristics were linear for three activation currents in the diode. From the V_F-T characteristics at 20 nA, 100 nA and 6 μA, the values of the temperature coefficients of the forward bias voltage (dV_F/dT) for the diode were determined as −2.30 mV K⁻¹, −2.60 mV K⁻¹ and −3.26 mV K⁻¹ with a standard error of 0.05 mV K⁻¹, respectively.     

The current–voltage and capacitance–voltage characteristics of molecularly modified β-carotene/n-type Si junction structure with fluorescein sodium salt

β-Carotene–FSS organic semiconductor/n-type Si structure has been characterized by current–voltage and capacitance–voltage methods. A deviation in I–V characteristic of the diode is observed due to effect of series resistance and interfacial layer. Cheung's functions were used to calculate diode parameters. The ideality factor, series resistance and barrier height values of the diode are n = 1.77, R_s = 10.32 (10.39) kΩ and 0.78 eV. The obtained ideality factor suggests that Au/β-carotene–FSS/n-Si Schottky diode has a metal–SiO₂ oxide layer plus organic layer–semiconductor (MIOS) configuration. The capacitance–voltage characterizations of Au/β-carotene–FSS/n-Si diode at different temperatures were performed. The capacitance of the diode changes with temperature. The barrier height and ideality factor obtained from C–V curves are 0.67 eV and 1.68. The interface density properties of the diode are analyzed and the shape of the density distribution of the interface states is in the range of E_c −0.49 to −0.62 eV. It is evaluated that the FSS organic layer controls electrical charge transport properties of Au/β-carotene/n-Si diode by excluding effects of the β-carotene and SiO₂ residual oxides on the hybrid diode.     

Temperature dependent current-voltage and capacitance-voltage characteristics of chromium Schottky contacts formed by electrodeposition technique on n-type Si

The variations in the electrical properties of Cr Schottky contacts formed by electrodeposition technique on n-type Si substrate have been investigated as a function of temperature using current-voltage (I-V) and capacitance-voltage (C-V) measurements in the temperature range of 80-320 K by steps of 20 K. The basic diode parameters such as ideality factor (n) and barrier height (Φ_b) were consequently extracted from the electrical measurements. It has been seen that the ideality factor increased and the barrier height decreased with decreasing temperature, when the I-V characteristics were analyzed on the basis of the thermionic emission (TE) theory. The abnormal temperature dependence of the Φ_b and n and is explained by invoking two sets of Gaussian distribution of barrier heights at 320-200 K, and 180-80 K. The double Gaussian distribution analysis of the temperature-dependent I-V characteristics of the Cr/n-type Si Schottky contacts gave the mean barrier heights of 0.910 and 0.693 eV and standard deviations (σ_s) of 109 mV and 72 mV, respectively. Then, these values of the mean barrier height have been confirmed with the modified ln(I₀/T²) − q²/2k²T² versus 1/T plot which belongs the two temperature regions.     

Effects of illumination on capacitance characteristics of Au/3C-SiC/p-Si/Al diode

Au/3C-SiC/p-Si/Al Schottky barrier diode was prepared using atmospheric pressure chemical vapor deposition technique. The device parameters such as barrier height, ideality factor, and series resistance were calculated using current-voltage characteristics, and were found to be 0.44 eV, 1.55, and 1.02 × 10⁴ Ω, respectively. The photocapacitive properties of the diode were studied under various illumination intensities. The transient photocapacitance measurements indicate that the capacitance of the Au/3C-SiC/p-Si/Al Schottky diode is very sensitive to illumination. The photocapacitance of the diode increases with increase in illumination intensity. The increase in photocapacitance with increase in illumination intensity suggests that these devices could be utilized as a photocapacitive sensor for optical sensors.     

Temperature dependent admittance spectroscopy of GaAs/AlGaAs single-quantum-well laser diodes (SQWLDs)

In this study, the main electrical parameters, such as doping concentration (N_D), barrier height (Φ_CV), depletion layer width (W_D), series resistance (R_s) and Fermi energy level (E_F), of GaAs/Al_xGa_1−xAs single quantum well (SQW) laser diodes were investigated using the admittance spectroscopy (C-V and G/ω-V) method in the temperature range of 80-360 K. The reverse bias C⁻² vs. V plots gives a straight line in a wide voltage region, especially in weak inversion region. The values of Φ_CV at the absolute temperature (T = 0 K) and the temperature coefficient (α) of barrier height were found as 1.22 eV and −8.65 × 10⁻⁴ eV/K, respectively. This value of α is in a close agreement with α of GaAs band gap (−5.45 × 10⁻⁴ eV/K). Experimental results show that the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the diode are affected by not only temperature but also R_s. The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/ω-V-T) characteristics confirmed that temperature and R_s of the diode have effects on the electronic parameters in SQW laser diodes.     

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current-voltage (I-V-T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6-8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100-320 K. The forward bias I-V-T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10¹⁴ eV⁻¹ cm⁻².     

The effect of a novel organic compound chiral macrocyclic tetraamide-I interfacial layer on the calculation of electrical characteristics of an Al/tetraamide-I/p-Si contact

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (I–V) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from I–V characteristics increases exponentially with bias from 5.81 × 10¹² cm⁻² eV⁻¹ at (0.59-E_v) eV to 1.02 × 10¹³ cm⁻² eV⁻¹ at (0.40-E_v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.     

Modification of electrical properties of the Au/1,1′ dimethyl ferrocenecarboxylate/n-Si Schottky diode

The electrical and interface state density properties of the Au/1,1′ dimethyl ferrocenecarboxylate (DMFC)/n-Si structure have been investigated by current–voltage, capacitance–voltage and conductance–frequency methods. The Au/DMFC/n-Si structure exhibits a rectifying behavior with a non-ideal I–V behavior with an ideality factor greater than unity. The ideality factor and barrier height of the Au/DMFC/n-Si Schottky diode is lower than that of Au/n-Si Schottky diode. The interface state density of the diode was determined from G/ω–f plots and was of order of 5.61 × 10¹² eV^?1 cm^?2. It is evaluated that the electrical properties of Au/n-Si diode is controlled using 1′ dimethyl ferrocenecarboxylate organic layer and in turn, Au/DMFC/n-Si structure gives new electronic parameters.     

Effects of post-annealing on Schottky contacts of Pt/ZnO films toward UV photodetector

The Schottky contact of Pt/ZnO was formed by depositing ZnO films oriented along c-axis by pulsed-laser deposition on Pt/Ti buffer layer supported by SiO₂/Si substrate. Effects of the post-annealing on the crystallinity, uniformity and native defects of ZnO film as well as Schottky contacts of Pt/ZnO films were investigated. Results show that the annealing can improve the crystallinity of ZnO film, suppress the native defects, and enhance the performance of Pt/ZnO Schottky contacts dramatically. The best Schottky diode shows the largest barrier height of 0.8 eV with reverse leakage current of 1.5 × 10⁻⁵ A/cm². The zero-biased photodetector based on the best Schottky diode possesses responsivity of 0.265 A/W at 378 nm, fast photo-response component with rise time of 10 ns and fall time of 17 ns. This report demonstrates possibility of ZnO films/Pt hetero-junction with large area Schottky contact, and establishes the potential of this material for use in UV photodetector devices.     

Electrical characterization of Au/Pd/n-GaN/Pd/Au device structure in the radio frequency range by simulation study

GaN based devices are highly promising optoelectronic devices for many years due to their useful applications in photovoltaic energy conversation, fiber optic communication and atmosphere monitoring. GaN based devices such as Schottky barrier, metal–semiconductor–metal and p-i-n structure have been fabricated and characterized so far. A proper understanding of the impedance or admittance spectroscopy result is crucial since it is a powerful tool to calculate the physical and electronic parameters of a device. In this study, temperature dependent dark current–voltage (I–V) and dark impedance spectra of n type GaN based metal–semiconductor–metal device have been studied with current–voltage and impedance spectra by simulation. All current–voltage characteristics exhibited good rectification behavior. The forward and reverse bias capacitance–voltage (C–V) characteristics of the Au/Pd/n-GaN/Pd/Au device were simulated at 2 MHz probing frequency. Nyquist plots of simulated device at 295 K are shown that two-barrier heights can be observable above critical threshold bias point. Frequency depended inverse dielectric loss tangent spectra of Au/Pd/n-GaN/Pd/Au device at different DC bias voltages also shows significant two peaks. This indicates that our simulation is extremely useful for determination of potential barrier numbers.     

Electrical properties of Al/conducting polymer (P2ClAn)/p-Si/Al contacts

Al/P2ClAn/p-Si/Al structure was obtained by the evaporation of the polymer P2ClAn on the front surface of p-type silicon substrate. The P2ClAn emeraldine salt was chemically synthesized by using propionic (C₂H₅COOH) acid. The current–voltage (I–V) characteristic of the structure was measured at room temperature. The capacitance–voltage–frequency (C–V–f) in terms of interface states over the frequency range of 10 kHz to 3 MHz has been investigated. The capacitance has decreased with increasing frequency, due to the interface states distribution. From the forward bias I–V plot for the sample, the ideality factor (n) and zero-bias barrier height (Φ_bp,0) were obtained as 4.84 and 0.787 eV, respectively. Under forward bias, the high value of the ideality factor and the dispersion in capacitance could be due to the interface state distribution, the interfacial insulator layer, the conducting polymer on the interface and inhomogeneity of the barrier height. The energy distributions and the relaxation times of the interface states were determined in the energy range of (0.387 − E_v) to (0.787 − E_v) eV.     

The calculation of electronic properties of an Ag/chitosan/n-Si Schottky barrier diode

In this study, the film of chitosan by adding the solution of chitosan being a polymeric compound on the top of an n-Si substrate and then by evaporating solvent was formed. It was seen that the chitosan/n-Si contact demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. Average barrier height and ideality factor values for this structure were determined as 0.94 eV and 1.81, respectively. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitosan/n-Si substrate in the energy range (E_c−0.785) to (E_c−0.522) eV have been determined from the I–V characteristics. The interface state density N_ss ranges from 5.39 × 10¹² cm⁻² eV⁻¹ in (E_c−0.785) eV to 1.52 × 10¹³ cm⁻² eV⁻¹ in (E_c−0.522) eV. The interface state density has an exponential rise with bias from the midgap towards the bottom of the conduction band.     

Synthesis of the pyrrolo[3,2-b]pyrrole-based copolymer with enhanced open circuit voltage

A new accepter unit, pyrrolo[3,2-b]pyrrole-2,5-dione, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor–acceptor pair for OPVs. Pyrrolo[3,2-b]pyrrole-2,5-dione unit, regioisomer of the known pyrrolo[3,4-c]pyrrole-1,4-dione, is originated from the structure of stable synthetic pigment. The new conjugated polymer with pyrrolo[3,2-b]pyrrole-2,5-dione, thiophene and carbazole was synthesized using Suzuki polymerization to generate P1. The solid thin film of P1 shows absorption band with maximum peaks at 374 and 548 nm, and the absorption onset at 679 nm, corresponding to band gap of 1.83 eV. The field-effect hole mobility of P1 is 2.2 × 10⁻⁵ cm²/Vs. The device based on the polymer:PCBM (1:2) blend without thermal treatment showed a V_OC of 0.82 V, a J_SC of 6.28 mA/cm², and an FF of 0.39, giving a PCE of 2.00%.     

Electrical and optical characteristics of Au/PbS/n-6H-SiC structures prepared by electrodeposition of PbS thin film on n-type 6H-SiC substrate

To realize Schottky barrier height (SBH) modification in the Au/n-6H-SiC Schottky diodes, lead sulfide (PbS) thin films were grown on n-6H-SiC by electrodeposition method. At first, XRD experiments were performed to investigate the crystal structure of the PbS film electrodeposited on n-6H-SiC. It has been deduced from the diffraction profile that the PbS thin film has a crystal structure more strongly oriented along the [2 0 0] direction. An optical energy band gap value of 1.42 eV for the PbS film was obtained from its optical absorption spectra. Then, we have prepared Au/PbS/n-6H-SiC Schottky barrier diodes (SBDs) with interface layer and reference Au/n-6H-SiC/Ni SBDs. The SBH enhancement has been succeeded by the PbS interlayer, influencing the space charge region of the SiC. The SBH values of 1.03 and 0.97 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. The SBH increase in the Au/PbS/n-6H-SiC SBD with the interfacial PbS layer has been attributed to the fact that the interface states contain a net negative interface charge in metal/n-type semiconductor contact due to the presence of the interfacial PbS layer.     

Multiple-barrier distribution behavior of Mo/p-GaTe fabricated with sputtering

A Molybdenum Schottky diode on unintentially doped p-GaTe was fabricated using DC sputtering. I-V characteristics of the fabricated diode were measured as a function of temperature at the range of 50-300 K. The barrier parameters of Mo/p-GaTe are interpreted using thermionic emission theory and inhomogeneities observed in the barrier are characterized with Gaussian distribution approach on the basis of parallel conduction model. The barrier height and the ideality factor values at 300 K and at 80 K of Mo/p-GaTe were calculated to be 0.581 eV, 1.097 and 0.472 eV, 1.349, respectively. The barrier parameters changed resolutely at 140-300 K temperature range and a strong temperature dependence was observed below 130 K. The weighting coefficients, standard deviations and mean barrier heights were calculated for sub distributions. Richardson plot was interpreted with a new approach and Richardson constant was found to be 117.96 AK⁻² cm⁻² for p-GaTe.     

The analysis of lateral distribution of barrier height in identically prepared Co/n-Si Schottky diodes

We have studied the experimental linear relationship between ideality factors and barrier heights (BHs) for Co/n-Si metal–semiconductor (MS) structures with a doping density of about 10¹⁵ cm⁻³. The barrier heights for the Co/n-type Si metal–semiconductor structures from the current–voltage (I–V) characteristics varied from 0.64 to 0.70 eV, the ideality factor n varied from 1.18 to 1.26, and from reverse bias capacitance–voltage (C⁻²–V) characteristics the barrier height varied from 0.68 to 0.81 eV. The experimental barrier height distributions obtained from the I–V and C⁻²–V characteristics were fitted by a Gaussian distribution function, and their mean values were found to be 0.67 and 0.75 eV, respectively. Furthermore, the lateral homogeneous BH value of approximately 0.81 eV for Co/n-Si metal–semiconductor structures was obtained from the linear relationship between experimental effective BHs and ideality factors.     

Conductivity and stability of cobalt pyrovanadate

Cobalt pyrovanadate was successfully synthesised by a solid state route and the conductivity in both oxidising and reducing environments was determined for the first time. Impedance measurements between 300 °C and 700 °C in air determined that Co₂V₂O₇ is an intrinsic semiconductor with activation energy of 1.16(3) eV. The conductivity in air reached a maximum of 4 × 10⁻⁴ S cm⁻¹ at 700 °C. Semiconducting behaviour was also observed in 5% H₂/Ar, albeit with a much smaller activation energy of 0.04(4) eV. Between 300 °C and 700 °C the conductivity ranged from 2.45 S cm⁻¹ to 2.68 S cm⁻¹, which is approaching the magnitude required for SOFC anode materials. Thermogravimetric analysis found a significant weight loss upon reduction of the compound. X-ray diffraction analysis, coupled with data from previous research, suggested compound degradation into Co_2−xV_1+xO₄, CoO and VO. The redox instability and the low conductivity lead us to the conclusion that cobalt pyrovanadate is unsuitable for utilisation as an anode material for SOFCs although the conductivity is reasonable in a reducing atmosphere.     

On the mechanism of current-transport in Cu/CdS/SnO2/In-Ga structures

The structural and optical properties of CdS films deposited by evaporation were investigated. X-ray diffraction study showed that CdS films were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. The study has been made on the behavior of Cu/n-CdS thin film junction on SnO₂ coated glass substrate grown using thermal evaporation method. The forward bias current-voltage (I-V) characteristics of Cu/CdS/SnO₂/In-Ga structures have been investigated in the temperature range of 130-325 K. The semi-logarithmic lnI-V characteristics based on the Thermionic emission (TE) mechanism showed a decrease in the ideality factor (n) and an increase in the zero-bias barrier height (Φ_Bo) with the increasing temperature. The values of n and Φ_Bo change from 8.98 and 0.29 eV (at 130 K) to 3.42 and 0.72 eV (at 325 K), respectively. The conventional Richardson plot of the ln(I_o/T²) vs q/kT shows nonlinear behavior. The forward bias current I is found to be proportional to I_o(T)exp(AV), where A is the slope of ln(I)-V plot and almost independent of the applied bias voltage and temperature, and I_o(T) is relatively a weak function of temperature. These results indicate that the mechanism of charge transport in the SnO₂/CdS/Cu structure in the whole temperature range is performed by tunneling among interface states/traps or dislocations intersecting the space-charge region. In addition, voltage dependent values of resistance (R_i) were obtained from forward and reverse bias I-V characteristics by using Ohm's law for each temperature level.     

Solid-state structure of the naphthalene-based n-type semiconductor,and performance improved with Mo-based source/drain electrodes

The synthesis, single-crystal structures, and device performance of novel naphthalene-diimide are described. The crystal structure has revealed the importance of a withdrawing group on solid-state packing. Metal molybdenum use as source/drain (S/D) electrodes can improve the performance of the bottom-contact device. The bottom-contact device based on a material of N,N′-bis (4-trifluoromethoxybenzyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide has a high mobility of 3.58 × 10⁻² cm² V⁻¹ s⁻¹, a threshold voltage of 1.3 V, and an on/off current ratio of 5.2 × 10⁵.