Influence of Annealing on Electrical Properties of an Organic Thin Layer-Based n-Type InP Schottky Barrier Diode

The electrical properties of a fabricated Au/polymethylmethacrylate (PMMA)/n-InP Schottky barrier diode have been analyzed for different annealing temperatures using current–voltage (I–V) and capacitance–voltage (C–V) techniques. It is observed that the Au/PMMA/n-InP structure shows excellent rectifying behavior. The extracted barrier height and ideality factor of the as-deposited Au/PMMA/n-InP Schottky contact are 0.68 eV (J–V)/0.82 eV (C–V) and 1.57, respectively. However, the barrier height (BH) of the Au/PMMA/n-InP Schottky contact increases to 0.78 eV (J–V)/0.99 eV (C–V) when the contact is annealed at 150°C for 1 min in nitrogen atmosphere. Upon annealing at 200°C, the BH value decreases to 0.72 eV (J–V)/0.90 eV (C–V) and the ideality factor increases to 1.48. The PMMA layer increases the effective barrier height of the structure by creating a physical barrier between the Au metal and the n-InP. Cheung’s functions are also used to calculate the series resistance of the Au/PMMA/n-InP structure. The interface state density (N _ss) is found to be 6.380 × 10¹² cm^?2 eV^?1 and 1.916 × 10¹² cm^?2 eV^?1 for the as-deposited and 150°C-annealed Au/PMMA/n-InP Schottky contacts, respectively. These results indicate that the interface state density and series resistance have a significant effect on the electrical characteristics of Au/PMMA/n-InP Schottky barrier devices. Finally, it is noted that the diode parameters change with increasing annealing temperature.     

Numerical simulation study of current–voltage characteristics of a Schottky diode with inverse doped surface layer

The Poisson’s equation and drift–diffusion equations are used to simulate the current–voltage characteristics of Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and current as a function of bias through the Schottky diode is calculated for various inverse layer thicknesses and doping concentrations. The Schottky diode parameters are then extracted by fitting of simulated current–voltage data into thermionic emission diffusion equation. The obtained diode parameters are analyzed to study the effect of inverse layer thickness and doping concentration on the Schottky diode parameters and its behavior at low temperatures. It is shown that increase in inverse layer thickness and its doping concentration give rise to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of Schottky barrier height and ideality factor are studied. The effect of temperature dependence of carrier mobility on the Schottky diode characteristics is also discussed.     

Electrical parameters of a DC sputtered Mo/n-type 6H-SiC Schottky barrier diode

A Mo/n-type 6H-SiC/Ni Schottky barrier diode (SBD) was fabricated by sputtering Mo metal on n-type 6H-SiC semiconductor. Before the formation of Mo/n-type 6H-SiC SBD, an ohmic contact was formed by thermal evaporation of Ni on n-type 6H-SiC and annealing at 950 °C for 10 min. It was seen that the structure had excellent rectification. The electrical parameters were extracted using its current–voltage (I–V) and capacitance–voltage (C–V) measurements carried out at room temperature. Very high (1.10 eV) barrier height and 1.635 ideality factor values were reported for Mo/n-type 6H-SiC using ln I–V plot. The barrier height and series resistance values of the diode were also calculated as 1.413 eV and 69 Ω from Norde׳s functions, respectively. Furthermore, 1.938 eV barrier height value of Mo/n-type 6H-SiC SBD calculated from C–V measurements was larger than the one obtained from I–V data.     

Numerical analysis of inhomogeneous Schottky diode with discrete barrier height patches

The potential profile inside the semiconductor at the metal–semiconductor contact is simulated by numerically solving the Poisson equation and the drift diffusion equations for inhomogeneous Schottky diode. From the simulated potential and the electron and hole concentrations, the drift-diffusion current as a function of bias is calculated. The simulation is carried out for various distribution patterns of barrier height patches at the metal–semiconductor contact to study the effect of barrier inhomogeneities on the Schottky diode parameters, namely barrier height and ideality factor and their temperature dependence. It is found that barrier height decreases and ideality factor increases with increase in the deviation of discrete barrier height patches in the distribution. The resulting barrier parameters are studied to understand the effect of barrier inhomogeneities on the current–voltage characteristics of inhomogeneous Schottky contact.     

Effect of Inverse Doped Surface Layer in Schottky Barrier Modification: A Numerical Study

Poisson’s equation and the drift–diffusion equations are used to simulate the current–voltage characteristics of a Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and then current as a function of bias through the Schottky diode is calculated. The Schottky diode parameters are extracted by fitting of simulated data to the thermionic emission diffusion equation. The simulation is carried out for various inverse layer thicknesses and doping concentrations. The obtained diode parameters are analyzed to study the effect of the inverse layer thickness and doping concentration on Schottky diode modification and its behavior at low temperatures. It is shown that an increase in the inverse layer thickness and doping concentration leads to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of the Schottky barrier height and ideality factor are also studied.     

Enhancement of effective barrier height in Ti-silicon Schottky diode using low-energy ion implantation

Increasing the effective barrier height in a Ti-p-type silicon Schottky diode has been achieved by means of low-energy ion implantation to introduce a thin inversion layer on silicon substrate. It is shown theoretically that effective barrier height equal to the energy bandgap can be obtained in such structure if the thickness and dopant density of the implanted layer are properly chosen. Experimental results for several titanium (Ti) on phosphorus implanted p-type silicon Schottky diodes show that effective barrier heights were increased from 0.6 eV for the Ti-p Si Schottky diode to 0.96 eV for a Ti-n-p-Si Schottky diode with a phosphorus-implanted layer thickness of 400 Å and dose of 1.26 × 10¹²cm^-2. Good agreement is obtained between the calculated and the measured barrier height for several Ti-n-p silicon Schottky diodes.     

Current-voltage characteristics of electric contacts on p-type ZnSe

The current-voltage characteristics of electric contacts made of different materials on p-type ZnSe that form Schottky barriers from 0.3 to 1.2 eV are studied theoretically using the formula $$J = \frac{{A^* T}}{k}\int_0^\infty {T(E)[F(E) - F(E - eV)]dE,} $$ where T(E) is the energy-dependent quantum tunneling probability and F(E) is the Fermi distribution function. The contribution to the total current of both the thermionic emission and the tunneling are therefore included. The net doping concentrations under study range from 1.0×10¹⁷ cm^?3 to 1.0×10¹⁹ cm^?3. The reverse bias voltage across the barrier at a current density of 200 A/cm² is used to assess whether the barrier is reduced to an ohmic contact. A barrier of 0.3 eV is already an ohmic contact at doping concentration p=1.0×10¹⁷ cm^?3, while a barrier of 1.2 eV still behaves like a diode event at p=1.0×10¹⁹ cm^?3.     

a-Si:H Schottky gate on n-GaInAs

The metal Schottky contact leads to low barrier heights on small-gap (<1 eV) semiconductors. This is the case of the n-type GaInAs material matched to InP where this barrier does not exceed 0.3 eV. We have found an original method to improve this result considerably by using a deposition of an amorphous semiconductor a-Si or a-Si: H. A Pt metal acts as the Schottky contact on the amorphous layer. The device behaves like a heterostructure of a high-gap (amorphous layer: Eg?1.8 eV) on a small-gap (GaInAs:0.75 eV) material. The Schottky-barrier height (0.8 eV) is greater than the GaInAs bandgap (0.75 eV). The reverse current is very low: 20 nA at 1 V reverse voltage for a 0.6 mm diode diameter. An FET using a-Si: H as a gate realised on a GaInAs layer shows a good electrical characteristic.     

Large‐Area Schottky Barrier Transistors Based on Vertically Stacked Graphene–Metal Oxide Heterostructures

The fabrication of all‐transparent flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene–metal oxide–metal heterostructures and ion gel gate dielectrics is demonstrated. The vertical SB transistor structure is formed by (i) vertically sandwiching a solution‐processed indium‐gallium‐zinc‐oxide (IGZO) semiconductor layer between graphene (source) and metallic (drain) electrodes and (ii) employing a separate coplanar gate electrode bridged with a vertical channel through an ion gel. The channel current is modulated by tuning the Schottky barrier height across the graphene–IGZO junction under an applied external gate bias. The ion gel gate dielectric with high specific capacitance enables modulation of the Schottky barrier height at the graphene–IGZO junction over 0.87 eV using a voltage below 2 V. The resulting vertical devices show high current densities (18.9 A cm^?2) and on–off current ratios (>10⁴) at low voltages. The simple structure of the unit transistor enables the successful fabrication of low‐power logic gates based on device assemblies, such as the NOT, NAND, and NOR gates, prepared on a flexible substrate. The facile, large‐area, and room‐temperature deposition of both semiconducting metal oxide and gate insulators integrates with transparent and flexible graphene opens up new opportunities for realizing graphene‐based future electronics.     

Specific contact resistance of the Ni/AuGe/nGaP system

This work studies the specific contact resistance for Ni/Au-Ge/nGaP system at the rectifying regime, i.e. for which the heat-treatment temperature is below 400°C and the I–V characteristics exhibit a rectifying behavior. The specific contact resistance is first computed by using the generalized majority carrier transport theory derived by Chang and Sze [1]. The computed theoretical results are then used to interpret the experimental data which are obtained by measuring the specific contact resistance, at zero bias, as a function of the temperature for as-deposited and heat-treated Ni/Au-Ge/nGaP Schottky diodes. Au/nGaP Schottky diodes are also fabricated to verify the theoretical results. It is found that the barrier height for the Ni/Au-Ge/nGaP system rises from the as-deposited value, 1.10±0.04 eV, to the value of the Ni/nGaP system, 1.27?0.02 eV, as the contact is heat-treated at various temperatures up to 360°C, the eutectic point of the Au-Ge system, and drops rapidly as the contact is heat-treated above 360°C. The barrier height rise is believed to be caused by the Ni in-diffusion toward the Au-Ge/nGaP interface during the heat-treatment. The smaller temperature dependence of the specific contact resistance for Schottky diode samples heat-treated above 360°C indicates that after heat-treatment above this temperature, an n⁺ layer is formed on the GaP surface. The theoretically computed results are used to fit the experimentally measured data to obtain the effective n⁺ doping concentrations and barrier heights.     

The effect of composition on the barrier height and contact resistance of Tixw1-x/si contacts

Barrier height is an important parameter for metal/silicon rectifying contacts. In this paper the barrier heights of Ti_xW{1-x}/Si contacts have been studied and found to range from 0.54 eV for high Ti content to 0.66 eV for pureW. Interpretation is made in terms of the parallel Schottky diode model of Tu. Ohmic contact measurements of Ti_xW_1-x/ Si metallization after heat treatment at 500° C have also been made and specific contact resistances of less than 10⁻⁶ ohm-cm² obtained in shallow implanted junction devices.     

Current–voltage characteristics of Schottky diode simulated using semiconductor device equations

The Poisson's equation and the drift diffusion equations have been used to simulate the current–voltage characteristics of Schottky diode. The potential variation inside the bulk semiconductor near the metal–semiconductor contact was estimated first and then the current as a function of bias through the Schottky diode using silicon parameters were calculated over a wide temperature range. From the simulated current–voltage characteristics the diode parameters were extracted by fitting of current–voltage data into thermionic emission diffusion current equation. The derived barrier parameters are analysed to study the effect of various parameters, e.g. semiconductor thickness, doping concentration, temperature dependence of carrier mobility and energy band gap, on the current–voltage characteristics of Schottky diode in view of the thermionic emission diffusion current equations.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

Numerical simulation of the inhomogeneous barrier height of an Au/n-InP Schottky diodeKamel Zeghdar1, Lakhdar Dehimi1, 2, Achour Saadoune1, Nouredine Sengouga1,*

We report the current-voltage(I-V) characteristics of the Schottky diode(Au/n-InP) as a function of temperature. The SILVACO-TCAD numerical simulator is used to calculate the I-V characteristic in the temperature range of 280-400 K. This is to study the effect of temperature on the I-V curves and assess the main parameters that characterize the Schottky diode such as the ideality factor, the height of the barrier and the series resistance. The I-V characteristics are analyzed on the basis of standard thermionic emission(TE) theory and the inhomogeneous barrier heights(BHs) assuming a Gaussian distribution. It is shown that the ideality factor decreases while the barrier height increases with increasing temperature, on the basis of TE theory. Furthermore, the homogeneous BH value of approximately 0.524 eV for the device has been obtained from the linear relationship between the temperature-dependent experimentally effective BHs and ideality factors. The modified Richardson plot, according to the inhomogeneity of the BHs, has a good linearity over the temperature range. The evaluated Richardson constant A^* was 10.32 A·cm^-2·K^-2, which is close to the theoretical value of 9.4 A·cm^-2·K^-2 for n-InP. The temperature dependence of the I-V characteristics of the Au/n-InP Schottky diode have been successfully explained on the basis of the thermionic emission(TE) mechanism with a Gaussian distribution of the Schottky barrier heights(SBHs). Simulated I-V characteristics are in good agreement with the measurements[Korucu D, Mammadov T S. J Optoelectronics Advanced Materials, 2012, 14:41]. The barrier height obtained using Gaussian Schottky barrier distribution is 0.52 eV, which is about half the band gap of InP.     

Controlling of electronic parameters of GaAs Schottky diode by poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic interlayer

The electronic properties of metal-organic semiconductor-inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current-voltage and capacitance-voltage methods. The Au/PEDOT/n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/n-GaAs/In (0.85 eV) and Au/n-GaAs/In Schottky diodes. The decrease in barrier height of Au/n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol).     

Electrical and Optical Characterization of Ni/Al0.3Ga0.7N/GaN Schottky Barrier Diodes

Ni/AlGaN/GaN Schottky barrier diodes were characterized by electrical and optical measurements. Analysis of temperature-dependent (80?K to 550?K) current–voltage characteristics considering various transport mechanisms shows that the tunneling current dominates in the samples investigated. Thermionic emission current, extracted from the total current by a fitting procedure, yielded an effective barrier height of 1.36?eV to 1.39?eV at 300?K, and its slight decrease with increased temperature. This result shows that significantly lower barrier heights reported before (0.73?eV to 0.96?eV) follow from an assumption that the measured and thermionic currents are equal. The barrier height of 1.66?eV extracted from photoemission measurements confirms that electrically evaluated barrier heights are underestimated. The tunneling current contribution is considered to be dislocation governed, and a dislocation density of about 2?×?10⁸?cm^?2 is calculated.     

6H-SiC Schottky二极管的正向特性

提出了一种考虑Schottky结势垒不均匀性和界面层作用的Si C Schottky二极管( SBD)正向特性模型,势垒的不均匀性来自于Si C外延层上的各种缺陷,而界面层上的压降会使正向Schottky结的有效势垒增高.该模型能够对不同温度下Si C Schottky结正向特性很好地进行模拟,模拟结果和测量数据相符.它更适用于考虑器件温度变化的场合,从机理上说明了理想因子、有效势垒和温度的关系.     

Barrier height diminution in Schottky diodes due to electrostatic screening

Electrostatic screening in the metal contact of a Schottky (metal-semiconductor) diode is shown to influence the calculated electrical characteristics of the diode. A thin space-charge layer is formed at the surface of the metal contact by capacitively induced free charges, This results in a voltage dependent diminution of the barrier height of the diode that increases in magnitude with increasing semiconductor dielectric constant and carrier concentration. Predicted values of the barrier height diminution exceed those attributed to image forces or tunneling effects for materials with dielectric constants greater than about 20. In diodes using semiconducting ferroelectric or piezoelectric materials, an additional diminution of the barrier height results from free charges induced in the metal contact by a remanent polarization field or an externally applied mechanical stress. Current-voltage characteristics of a metal-semiconductor diode are shown to be significantly influenced by the electrostatic screening effect. A soft breakdown current as opposed to saturation current is predicted for reverse biases while an exponential forward current with an η coefficient exceeding unity is predicted for forward biases. Photoemission characteristics are also affected. A voltage-dependent diminution of the threshold energy for photoresponse is predicted. Capacitance-voltage characteristics, on the other hand, differ only slightly from those of an ideal Schottky diode except in the case of a ferroelectric diode where excessively large screening effects are possible.     

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.     

Barrier height engineering on GaAs THz Schottky diodes by means ofhigh-low doping, InGaAs- and InGaP-layers

Barrier height engineering of n-GaAs-based millimeter-wave Schottky diodes using strained InGaAs/GaAs and InGaP/GaAs heterostructures and a high doping surface layer is presented. The Schottky barrier height can be varied between Φ_fb=0.52 eV and Φ_fb=1.0 eV. The use of a pseudomorphic InGaAs layer and/or a thin high doping layer at the surface significantly reduces the Schottky barrier height. This is advantageous for low-drive zero bias mixing applications, A full quantum mechanical numerical calculation is presented to simulate the influence of different high doping layer thicknesses on the diode's dc characteristic. The theoretical results are compared with experimental results, For reverse bias applications (e.g., varactors) a barrier height and breakdown voltage enhancement is realized with a lattice matched InGaP/GaAs heterostructure. The barrier height value is determined by temperature dependent dc-measurements. The epitaxial layered structures are grown by molecular beam epitaxy. The diode devices are fabricated in a fully planar technology using selective oxygen implantation for lateral isolation. The diode's cut-off frequencies are in the THz-range