The temperature dependent analysis of Au/TiO2 (rutile)/n-Si (MIS) SBDs using current–voltage–temperature (I–V–T) characteristics

In this study, the main electrical parameters of Au/TiO₂(rutile)/n-Si Schottky barrier diodes (SBDs) were analyzed by using current–voltage–temperature (I–V–T) characteristics in the temperature range 200–380 K. Titanium dioxide (TiO₂) thin film was deposited on a polycrystalline n-type Silicon (Si) substrate using the DC magnetron sputtering system at 200 °C. In order to improve the crystal quality deposited film was annealed at 900 °C in air atmosphere for phase transition from amorphous to rutile phase. The barrier height (Φ_b) and ideality factor (n) were calculated from I–V characteristics. An increase in the value of Φ_b and a decrease in n with increasing temperature were observed. The values of Φ_b and n for Au/TiO₂(rutile)/n-Si SBDs ranged from 0.57 eV and 3.50 (at 200 K) to 0.82 eV and 1.90 (at 380 K), respectively. In addition, series resistance (R_s) and Φ_b values of MIS SBDs were determined by using Cheung's and Norde's functions. Cheung's plots are obtained from the donward concave curvature region in the forward bias semi-logarithmic I–V curves originated from series resistance. Norde's function is easily used to obtain series resistance as a function of temperature due to current counduction mechanism which is dominated by thermionic emission (TE). The obtained results have been compared with each other and experimental results show that R_s values exhibit an unusual behavior that it increases with increasing temperature.     

A detailed comparative study on the main electrical parameters of Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes

We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s), and shunt resistance (R_sh) with values of 1.38, 0.75 eV, 97.64 Ω, and 203 MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62 eV, 164.15 Ω and 0.597 MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (N_ss). The values of N_ss range from 1.36×10¹² at E_c—0.569 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.387 eV for Au/PVA:Zn/n-Si SBD and 3.34×10¹² at E_c—0.560 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.424 eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.     

The effects of surface states and series resistance on the performance of Au/SnO2/n-Si and Al/SnO2/p-Si (MIS) Schottky barrier diodes

We have fabricated two types of Schottky barrier(SBDs),Au/SnO₂/n-Si (MIS1) and Al/SnO₂/p-Si (MIS2), to investigate the surface (N_ss) and series resistance (R_s) effect on main electrical parameters such as zero-bias barrier height (Φ_Bo) and ideality factor (n) for these SBDs. The forward and reverse bias current–voltage (I–V) characteristics of them were measured at 200 and 295 K, and experimental results were compared with each other. At temperatures of 200 and 295 K, Φ_Bo, n, N_ss and R_s for MIS1 Schottky diodes (SDs) ranged from 0.393 to 0.585 eV, 5.70 to 4.75, 5.42×10¹³ to 4.27×10¹³ eV^?1 cm^?2 and 514 to 388 Ω, respectively, whereas for MIS2 they ranged from 0.377 to 0.556 eV, 3.58 to 2.1, 1.25×10¹⁴ to 3.30×10¹⁴ eV^?1 cm^?2 and 312 to 290 Ω, respectively. The values of n for two types of SBDs are rather than unity and this behavior has been attributed to the particular distribution of N_ss and interfacial insulator layer at the metal/semiconductor interface. In addition, the temperature dependence energy density distribution profiles of N_ss for both MIS1 and MIS2 SBDs were obtained from the forward bias I–V characteristics by taking into account the bias dependence of effective barrier height (Φ_e) and R_s. Experimental results show that both N_ss and R_s values should be taken into account in the forward bias I–V characteristics. It has been concluded that the p-type SBD (MIS2) shows a lower barrier height (BH), lower R_s, n and N_ss compared to n-type SBD (MIS1), which results in higher current at both 200 and 295 K.     

Evaluation of lateral barrier height of inhomogeneous photolithography-fabricated Au/n-GaAs Schottky barrier diodes from 80 K to 320 K

In order to evaluate current conduction mechanism in the Au/n-GaAs Schottky barrier diode (SBD) some electrical parameters such as the zero-bias barrier height (BH) Φ_bo(I–V) and ideality factor (n) were obtained from the forward bias current–voltage (I–V) characteristics in wide temperature range of 80–320 K by steps of 10 K. By using the thermionic emission (TE) theory, the Φ_bo(I–V) and n were found to depend strongly on temperature, and the n decreases with increasing temperature while the Φ_bo(I–V) increases. The values of Φ_bo and n ranged from 0.600 eV and 1.51(80 K) to 0.816 eV and 1.087 (320 K), respectively. Such behavior of Φ_bo and n is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of BHs at Au/n-GaAs interface. In the calculations, the electrical parameters of the experimental forward bias I–V characteristics of the Au/n-GaAs SBD with the homogeneity in the 80–320 K range have been explained by means of the TE, considering GD of BH with linear bias dependence.     

Ultraviolet photodetectors based on low temperature processed ZnO/PEDOT:PSS Schottky barrier diodes

In this work, vertical Schottky barrier diodes (SBDs) were fabricated using a thin film of ZnO (50 nm) and PEDOT:PSS deposited by RF Sputtering and micro-drop casting, respectively. ITO and Au were used as ohmic contacts to ZnO and PEDOT:PSS films, respectively. The final structure consisted on Glass/ITO/ZnO/PEDOT:PSS/Au. The SBDs performance was characterized under dark and four different wavelengths conditions. From current–voltage characteristics, under dark and ambient conditions, a diode ideality factor of 1.4; a saturation current density of 1×10⁻⁹ A/cm²; a Schottky barrier height of 0.9 eV and a rectification ratio of 5 orders of magnitude at ±1 V were obtained. A carrier density of 5×10¹⁷ cm⁻³ for the ZnO film was estimated from capacitance–voltage measurements. For their characterization as photodiodes, the SBDs were illuminated with an ultra-bright UV (~380 nm) LED. A maximum UV responsivity of 0.013 A/W was obtained. The transient response of the SBDs was also analyzed with the UV LED connected to a pulsed signal of 0.5 Hz, demonstrating rise and fall times in the order of 200 ms. With a low temperature processing (<80 °C), visible-blind and UV photon-detection characteristics, the fabricated SBDs are candidates for flexible optoelectronics devices such as optical receivers for digital signal processing and measurement of light intensity.     

High-performing transparent photodetectors based on Schottky contacts

Transparent UV-photodetectors exhibiting very high responsivity and fast operation are discussed. Schottky contact photoelectric devices utilizing wide band gap TiO₂ absorber layer were evaluated for their performances as UV-photodetectors. Three different work function metals Cu, Mo and Ni were used to realize Schottky barrier with TiO₂. Ni Schottky contacts were found to be most suitable to fabricate high responsivity (2.034 A/W) photodetector with faster rise time (0.14 ms) and wide linear dynamic range (128 dB) operating at small applied reverse bias of −1 V. However, higher barrier height in the case of Mo/TiO₂ interface resulted in lowest dark current density of the value 2.21×10⁻⁸ A/cm² with quick fall time of 0.52 ms. The modulation of the barrier height would provide a route for designing fast and high responsive Schottky photodetector with broad linear dynamic range performance.     

Determination of contact parameters of Ni/n-GaP Schottky contacts

The electrical analysis of Ni/n-GaP structure has been investigated by means of current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) measurements in the temperature range of 120–320 K in dark conditions. The forward bias I–V characteristics have been analyzed on the basis of standard thermionic emission (TE) theory and the characteristic parameters of the Schottky contacts (SCs) such as Schottky barrier height (SBH), ideality factor (n) and series resistance (R_s) have been determined from the I–V measurements. The experimental values of SBH and n for the device ranged from 1.01 eV and 1.27 (at 320 K) to 0.38 eV and 5.93 (at 120 K) for Ni/n-GaP diode, respectively. The interface states in the semiconductor bandgap and their relaxation time have been determined from the C–f characteristics. The interface state density N_ss has ranged from 2.08 × 10¹⁵ (eV^?1 m^?2) at 120 K to 2.7 × 10¹⁵ (eV^?1 m^?2) at 320 K. C_ss has increased with increasing temperature. The relaxation time has ranged from 4.7 × 10^?7 s at 120 K to 5.15 × 10^?7 s at 320 K.     

Transport properties of Gallium Phosphide based Schottky contact with thin insulating layer

The current-voltage (I-V) characteristics of Au/n-GaP Schottky barrier diode was analyzed in wide temperature range of 220–400 K. The conduction mechanism in the low bias region, except for 220 K and 240 K, was identified as tunneling (TN). Nevertheless, thermionic emission (TE) becomes dominant as the voltage increases. The diode parameters were evaluated in this region by TE model incorporating the concept of thin insulating layer. The series resistance (R_s) of the device was found to decrease with increase in temperature. In the 220–320 K temperature range, as reported for most of the Schottky diodes, the zero-bias barrier height (ϕ_b0) decreases and the ideality factor (η) increases with the decrease of temperature. The value of modified Richardson constant (A**) obtained agrees well with the theoretical value. However, in the 320–400 K range, the variation of η and ϕ_b0 with temperature shows opposite trend, which is speculated as due to the change in conduction pattern by the temperature induced modifications at the interface.     

Current–voltage and capacitance–voltage characteristics of Al Schottky contacts to strained Si-on-insulator in the wide temperature range

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm⁻² K⁻² at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm⁻² K⁻²).     

Investigations on the annealing behavior of high-energy carbon irradiated Au/n-GaAs Schottky barrier diodes

Au Schottky barrier diodes (SBDs) have been irradiated using high-energy carbon ion fluences of 1×10¹¹, 1×10¹² and 1×10¹³ cm⁻². Current–voltage characteristics of unirradiated and irradiated diodes have been analyzed. The change in reverse leakage current increases with increasing ion fluence due to the irradiation-induced defects at the interface. The diodes were annealed at 523 and 623 K to study the effect of annealing. The rectifying behavior of the irradiated SBDs improves at 523 K. But at 623 K, the diode behavior deteriorates irrespective of the fluences. Better enhancement in the barrier height and also improvement in the ideality factor of the diodes has been observed at the annealing temperature of 523 K. Scanning Electron Microscopic analysis was carried out on the irradiated samples to delineate the projected range of the defects by high-energy carbon ion irradiation.     

The effect of annealing temperature on the electronic parameters and carrier transport mechanism of Pt/n-type Ge Schottky diode

The Pt nano-film Schottky diodes on Ge substrate have been fabricated to investigate the effect of annealing temperature on the characteristics of the device. The germanide phase between Pt nano-films and Ge substrate changed and generated interface layer PtGe at 573 K and 673 K, Pt₂Ge₃ at 773 K. The current–voltage(I - V) characteristics of Pt/n-Ge Schottky diodes were measured in the temperature range of 183–303 K. Evaluation of the I - V data has revealed an increase of zero-bias barrier height Φ_B0 but the decrease of ideality factor n with the increase in temperature. Such behaviors have been successfully modeled on the basis of the thermionic emission mechanism by assuming the presence of Gaussian distributions. The variation of electronic transport properties of these Schottky diodes has been inferred to be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. Therefore, the control of Schottky barrier height at metal/Ge interface is important to realize high performance Ge-based CMOS devices.     

Electrical and optical properties of Cu2ZnSnS4 grown by a thermal co-evaporation method and its diode application

Cu₂ZnSnS₄ (CZTS) is low cost and constitutes non-toxic materials abundant in the earth crust. Environment friendly solar cell absorber layers were fabricated by a thermal co-evaporation technique. Elemental composition of the film was stated by energy dispersive spectroscopy (EDS). Some optical and electrical properties such as absorption of light, absorption coefficient, optical band gap charge carrier density, sheet resistance and mobility were extracted. Optical band gap was found to be as 1.44 eV, besides, charge carrier density, resistivity and mobility were found as 2.14×10¹⁹ cm⁻³, 8.41×10⁻⁴ Ω cm and 3.45×10² cm² V⁻¹ s⁻¹, respectively. In this study Ag/CZTS/n-Si Schottky diode was fabricated and basic diode parameters including barrier height, ideality factor, and series resistance were concluded using current–voltage and capacitance–voltage measurements. Barrier height and ideality factor values were found from the measurements as 0.81 eV and 4.76, respectively, for Ag/CZTS/n-Si contact.     

Characteristics of RF reactive sputter-deposited Pt/SiO2/n-InGaN MOS Schottky diodes

All RF sputtering-deposited Pt/SiO₂/n-type indium gallium nitride (n-InGaN) metal–oxide–semiconductor (MOS) diodes were investigated before and after annealing at 400 °C. By scanning electron microscopy (SEM), the thickness of Pt, SiO_2, n-InGaN layer was measured to be ~250, 70, and 800 nm, respectively. AFM results also show that the grains become a little bigger after annealing, the surface topography of the as-deposited film was smoother with the rms roughness of 1.67 nm and had the slight increase of 1.92 nm for annealed sample. Electrical properties of MOS diodes have been determined by using the current–voltage (I–V) and capacitance–voltage (C–V) measurements. The results showed that Schottky barrier height (SBH) increased slightly to 0.69 eV (I–V) and 0.82 eV (C–V) after annealing at 400 °C for 15 min in N₂ ambient, compared to that of 0.67 eV (I–V) and 0.79 eV (C–V) for the as-deposited sample. There was the considerable improvement in the leakage current, dropped from 6.5×10⁻⁷ A for the as-deposited to 1.4×10⁻⁷ A for the 400 °C-annealed one. The annealed MOS Schottky diode had shown the higher SBH, lower leakage current, smaller ideality factor (n), and denser microstructure. In addition to the SBH, n, and series resistance (R_s) determined by Cheungs׳ and Norde methods, other parameters for MOS diodes tested at room temperature were also calculated by C–V measurement.     

Electrical properties of Π-conjugated Fe-TPP molecular solar cell device

A heterojunction device of Au/Fe-TPP/n-Si/Al was assembled by thermally evaporated deposition. The dark current density–voltage characteristics of device were investigated. Results showed a rectification behavior. Measurements of thermo electric power confirm that Fe-TPP thin film behaves as p-type semiconductors. Electronic parameters such as barrier height, diode ideality factor, series resistance, shunt resistance were found to be 0.83 eV, 1.5, 7 × 10⁵ Ω and 2 × 10¹⁰ Ω, respectively. The Au/Fe-TPP/n-Si/Al device indicates a photovoltaic behavior with an open circuit voltage V_oc of 0.52 V, short circuit current I_sc of 2.22 × 10^?6 A, fill factor FF of 0.49 and conversion efficiency 1.13% under white light illumination power 50 W/m².     

Characterization of an Au/n-Si photovoltaic structure with an organic thin film

We demonstrate that a copper(II) organic complex can control the electrical characteristics of conventional Au/n-Si metal–semiconductor (MS) contacts. We investigated the electronic and photovoltaic properties of a Cu(II) complex/n-Si heterojunction diode. The ideality factor n and barrier height Φ_b of the diode were 2.22 and 0.736 eV, respectively. An ideality factor greater than unity indicates that the diode exhibits non-ideal current–voltage behavior. This behavior results from the effect of series resistance and the presence of an interfacial layer. The series resistance and barrier height determined using Norde’s method were 6.7 kΩ and 0.77 eV, respectively. The device showed photovoltaic behavior, with a maximum open-circuit voltage of 0.24 V and a short circuit current of 1.7 μA under light of 8 mW/cm².     

Low-operating-voltage polymeric transistor with solution-processed low-k polymer/high-k metal-oxide bilayer insulators

We have successfully demonstrated a polymeric semiconductor-based transistor with low-k polymer/high-k metal-oxide (TiO₂) bilayer as gate dielectric. The TiO₂ layers are readily processable from solution and cured at low temperature, instead of traditionally sputtering or high temperature sintering process, thus may suitable for a low-cost organic field effect transistors (FETs) manufacture. The low-k polymer capped on TiO₂ layer could further smooth the TiO₂ dielectric surface and suppress the leakage current from grain boundary of TiO₂ films. The resulting unpatented P3HT-OFETs could operate with supply voltage less than 10 V and the mobility and threshold voltage were 0.0140 cm²/V s and 1.14 V, respectively. The on/off ratio was 1.0 × 10³.     

Fabrication and electrical characterization of Al/p-ZnIn2Se4 thin film Schottky diode structure

Polycrystalline thin films of ternary ZnIn₂Se₄ compound with p-type conductivity were deposited on a pre-deposited aluminium (Al) film by a flash evaporation technique. A Schottky diode comprising of Al/p-ZnIn₂Se₄ structure was fabricated and characterized in the temperature range 303–323 K in dark condition. The Schottky diode was subjected to current (I)-voltage (V) and capacitance (C)-voltage (V) characterization. The Al/p-ZnIn₂Se₄ Schottky diode showed behaviour typical of a p-n junction diode. The devices showed very good diode behaviour with the rectification ratio of about 10⁵ at 1.0 V in dark. The Schottky diode ideality factor, barrier height, carrier concentration, etc. were derived from I-V and C-V measurements. At lower applied voltages (V≤0.5 V), the electrical conduction was found to take place by thermionic emission (TE) whereas at higher voltages (V>0.5 V), a space charge limited conduction mechanism (SCLC) was observed. An energy band diagram was constructed for fabricated Al/p-ZnIn₂Se₄ Schottky diode.     

Drivability improvement in Schottky barrier source/drain MOSFETs with strained-Si channel by Schottky barrier height reduction

Due to an extra barrier between source and channel, the drivability of Schottky barrier source/drain MOSFETs (SBMOSFETs) is smaller than that of conventional transistors. To reach the drivability comparable to the conventional MOSFET, the Schottky barrier height (SBH) should be lower than a critical value. It is expected that SBH can be effectively reduced by a bi-axially strain on Si. In this letter, p-channel MOSFETs with PtSi Schottky barrier source/drain, HfAlO gate dielectric, HfN/TaN metal gate and strained-Si channel are demonstrated for the first time using a simplified low temperature process. Devices with the channel length of 4 μm have the drain current of 9.5 μA/μm and the transconductance of 14 μS/μm at V_gs − V_th = V_ds = −1 V. Compared to the cubic Si counterpart, the drain current and the transconductance are improved up to 2.7 and 3.1 times respectively. The improvement is believed to arising from the reduced barrier height of the PtSi/strained-Si contact and the enhanced hole mobility in the strained-Si channel.     

Electrical and photovoltaic properties of SnSe/Si heterojunction

Thin film of SnSe is deposited on n-Si single crystal to fabricate a p-SnSe/n-Si heterojunction photovoltaic cell. Electrical and photoelectrical properties have been studied by the current density–voltage (J–V) and capacitance–voltage (C–V) measurements at different temperatures. The fabricated cell exhibited rectifying characteristics with a rectification ratio of 131 at ±1 V. At low voltages (V<0.55 V), the dark forward current density is controlled by the multi-step tunneling mechanism. While at a relatively high voltage (V>0.55 V), a space charge-limited-conduction mechanism is observed with trap concentration of 2.3×10²¹ cm⁻³. The C–V measurements showed that the junction is of abrupt nature with built-in voltage of 0.62 V which decreases with temperature by a gradient of 2.83×10⁻³ V/K. The cell also exhibited strong photovoltaic characteristics with an open-circuit voltage of 425 mV, a short-circuit current density of 17.23 mA cm⁻² and a power conversion efficiency of 6.44%. These parameters have been estimated at room temperature and under light illumination provided by a halogen lamp with an input power density of 50 mW cm⁻².     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.