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.     

Observation of electron traps in electrochemically deposited CdTe films

The I–V and C-V data of Schottky devices formed on electrodeposited n-CdTe films are interpreted to determine the principle trap energy and density. The observed trap is an electron trap located at 0.55 eV below the conduction band with a density of ～7 × 10¹⁵/cm³. This correlates well with the values reported for CdTe prepared by different methods. Nickel is found to be an injecting contact to electrodeposited CdTe films. Au/n-CdTe barrier height is determined to be 0.75–0.85 eV for Schottky devices.     

A computer-aided simulation model for the I–V characteristic of M-n-p silicon Schottky-barrier diodes produced by use of low-energy arsenic-ion implantation

Current-transport properties of Al-n-p silicon Schottky-barrier diodes have been studied both experimentally and theoretically. An analytical model for the I-V characteristic of a metal-n-p Schottky barrier diode has been developed by using an interfacial layer-thermionic-diffusion model. Assuming a Gaussian distribution for the implanted profile, the barrier-height enhancement and ideality factor have been derived analytically. Using low energy (25 KeV) arsenic implantation with the dose ranged form 8 × 10¹⁰/cm² to 10¹²/cm², Al-n-p silicon Schottky barrier diodes have been fabricated and characterized. Comparisons between the experimental measurements and the results of computer simulations have been performed and satisfactory agreements between these comparisons have been obtained. The reverse I–V characteristics of the fabricated Al-n-p silicon Schottky barrier diodes can also be well simulated by the developed model.     

Analysis of contact effects in fully printed p-channel organic thin film transistors

Contact effects have been analyzed in fully printed p-channel OTFTs based on a pentacene derivative as organic semiconductor and with Au source–drain contacts. In these devices, contact effects lead to an apparent decrease of the field effect mobility with decreasing L and to a failure of the gradual channel approximation (GCA) in reproducing the output characteristics. Experimental data have been reproduced by two-dimensional numerical simulations that included a Schottky barrier (Φ_b = 0.46 eV) at both source and drain contacts and the effects of field-induced barrier lowering. The barrier lowering was found to be controlled by the Schottky effect for an electric field E < 10⁵ V/cm, while for higher electric fields we found a stronger barrier lowering presumably due to other field-enhanced mechanisms. The analysis of numerical simulation results showed that three different operating regimes of the device can be identified: (1) low |V_ds|, where the channel and the Schottky diodes at both source and drain behave as gate voltage dependent resistors and the partition between channel resistance and contact resistance depends upon the gate bias; (2) intermediate V_ds, where the device characteristics are dominated by the reverse biased diode at the source contact, and (3) high |V_ds|, where pinch-off of the channel occurs at the drain end and the transistor takes control of the current. We show that these three regimes are a general feature of the device characteristics when Schottky source and drain contacts are present, and therefore the same analysis could be extended to TFTs with different semiconductor active layers.     

Schottky contacts to high-resistivity epitaxial GaAs layers for detectors of particles and X- or γ-ray photons

The electrical characteristics of Ti and Pt Schottky contacts to epitaxial n-GaAs layers with the charge-carrier concentration <10¹² cm^?3 for detectors of particles and X- or ??-ray photons are studied. It is shown that it is preferable to use a diffusion-based theory of charge transport in calculations of the parameters of Schottky contacts to thick high-resistivity lightly compensated GaAs layers. The calculated barrier heights were 0.84 and 0.87 eV for the Ti and Pt contacts, respectively. The fabricated samples of the surface-barrier detectors featured a linear response in the studied range of energies from 6 to 140 keV for ??-ray photons and from 4 to 8 MeV for ?? particles; the efficiency of charge collection was close to 100% and the energy resolution was high at room temperature.     

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.     

Electrical characteristics of laser-contacted diodes

We have fabricated p⁺-n and Schottky diodes with contacts made of laser-formed palladium-silicide. The electrical characteristics of these diodes are presented. The reverse currents and breakdown voltages are comparable to conventionally contacted p⁺-n diodes. The barrier height of laser-formed Schottky diodes agrees well with published values for Pd₂Si. The promising results point out the potential applications of contact formation by laser irradiation in device manufacture.     

Analysis of Schottky Barrier Height in Small Contacts Using a Thermionic‐Field Emission Model

This paper reports on estimating the Schottky barrier height of small contacts using a thermionic‐field emission model. Our results indicate that the logarithmic plot of the current as a function of bias voltage across the Schottky diode gives a linear relationship, while the plot as a function of the total applied voltage across a metal‐silicon contact gives a parabolic relationship. The Schottky barrier height is extracted from the slope of the linear line resulting from the logarithmic plot of current versus bias voltage across the Schottky diode. The result reveals that the barrier height decreases from 0.6 eV to 0.49 eV when the thickness of the barrier metal is increased from 500 Å to 900 Å. The extracted impurity concentration at the contact interface changes slightly with different Ti thicknesses with its maximum value at about 2.9×10²⁰ cm^?3, which agrees well with the results from secondary ion mass spectroscopy (SIMS) measurements.     

Hafnium-ntype silicon Schottky barriers

This paper describes the electrical properties of hafnium-/n-type/silicon contacts. These contacts were found to be Schottky barriers with a low barrier height. Polished and chemically cleaned 〈111〉 silicon wafers with a donor concentration N_d = 7 × 10²² m^?3 were used to fabricate experimental Schottky barrier structures. For the Schottky barrier height φ_bn and the ideality factor n values were found of 0.47 V and 1.07–1.11, respectively. It is concluded that due to their low forward voltage drop and good rectifying properties, Hf-nSi contacts can be applied in microwave Schottky barrier diodes.     

Characteristics of an aluminum-germanium photovoltaic cell

Aluminum n-type germanium Schottky barrier photovoltaic cells with response in the medium IR range have been developed. Using a low temperature process, Al is sputtered onto Ge to form a barrier contact; a special arrangement of the top electrode has been used for enhancement the long wavelength photon absorptio. I–V characteristics, spectral response and ⁴He ion backscattering data of the device are presented.     

Al contacts to nanoroughened p-GaN

Nanoroughening of a p-GaN surface using nanoscale Ni islands as an etch mask was utilized to investigate the feasibility for the flip-chip configuration light-emitting diodes (LEDs) using an Al-based reflector. Improved ohmic characteristics were found for the nanoroughened sample. A specific contact resistivity of 8.9×10⁻² Ω cm² and a reflectance of 82% at 460 nm were measured for the nanoroughened Al contact. The Schottky barrier heights were decreased from 0.81 eV (I-V) and 0.84 eV (Norde) for the Al contact to 0.70 eV (I-V) and 0.69 eV (Norde) for the nanoroughened Al contact. The barrier height reduction may be attributed to enhanced tunneling and the increased contact area due to the nanoroughening. This work suggests that the ohmic contact characteristics and the light extraction efficiency may be improved further with a well-defined nanopatterned p-GaN layer.     

Schottky barrier heights of contact metals to p-type ZnSe

Schottky barrier heights (SBHs) of a variety of metals (In, Cd, Nb, Ti, W, Cu, Ag, Au, Ni, Pt, and Se) contacting to p-ZnSe grown by a molecular beam epitaxy method were determined by analyzing capacitance-voltage (C-V) and/or current density-voltage (J-V) curves. The SBH values of the Au and Ni contacts were determined from intersections of straight lines of the C⁻²-V curves to be 1.23 and 1.13 eV, respectively. The J-V calculations provided a large SBH value of 1.2 ± 0.1 eV for a variety of metals, indicating that the Fermi-level could be pinned at the contact interface. Reduction of the SBH values to a level lower than 0.4 eV and/or increase of doping concentrations to a level higher than 10²⁰ cm⁻³ are essential to obtain an ohmic contact with contact resistivity of around 10⁻³ Ω·cm².     

Two dimensional Schottky contact structure based on in-plane zigzag phosphorene nanoribbon

We investigate the transport properties of Schottky contact structure based on zigzag phosphorene nanoribbon (ZPNR) by using the non-equilibrium Green's function formalism with density functional theory. The calculated band structures show the unpassivated ZPNR is metal and the H-passivated ZPNR is semiconductor. The in-plane contact structure of unpassivated ZPNR and H-passivated ZPNR leads to the formation of a Schottky barrier, which results in rectifying current-voltage characteristics. The rectification ratio (RR) can reach to 10³ in the bias region from 0.3 V to 0.5 V. By extending the length of H-passivated ZPNR in Schottky contact structure, the currents of the Schottky contact structure are decreased, but the RR can be enlarged obviously. When the length of H-passivated ZPNR is four times than that of the unpassivated ZPNR, the average RR increases to 10⁶ in the bias region from 0.3 V to 0.5 V and the maximal RR is boosted up to 10⁷ at 0.45 V.     

Technological Fabrication Features of Microwave Device with Schottky Barriers

At present, research and development of heterojunctions are conducted in the directions of searching for new compositions and technological regimes for the creation of ohmic and barrier transitions for gallium arsenide. The transition to silver-based metallization, which has large thermal and electrical conductivity comparing with gold and a relatively low diffusion coefficient to gallium arsenide, should improve the technical characteristics of the devices. One of the most important technological operations in the formation of Schottky ohmic contacts and barriers is thermal annealing. Silver to gallium arsenide contacts are made in vacuum by the method of thermal evaporation. The deposition and thermal treatment regimes for creating ohmic contacts of Ag–Ge–In/n–n⁺ GaAs with specific contact resistance ρ_c = (5...7)+10^–5 Ω.cm² are developed. The influence of the substrate temperature during the silver deposition and the annealing temperature on the height of the Schottky barrier Ag/n–n⁺ GaAs, the injection coefficient γ and the nonideality factor η is established.     

Influence of metal sheet resistivity on the IV-characteristics of metal-semiconductor diodes

Thin metal films used as Schottky contacts to semiconductors are sometimes connected in one spot only. The change of the forward IV-characteristics then caused by the finite sheet conductivity of the metal film is considered, using a model which is solved by computer techniques. The results are plotted as the deviations from the usual ln I_fvvs V_fv linear plots, for different ratios of the radii R and r₀ of the C circular metal contact and the connecting wire, and with the sheet resistivity of the metal film as a parameter. The calculations are performed for the barrier height φ_Bn = 0.79 eV. The effective series resistance of the contact wire-sheet-platelet system varies with current, but is of the order of the sheet resistivity of the film, for R/r₀ ratios region of ～20–100.     

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.     

Theoretical analysis of a novel MPN gallium arsenide Schottky barrier solar cell

Theoretical analysis for a novel Au-p-n GaAs Schottky barrier solar cell has been made in this note. It is shown that barrier height equal to the energy band gap of GaAs can be obtained in the proposed cell structure if the thickness and dopant density of the p-GaAs layer are properly chosen. Calculations of the barrier height as function of the thickness and dopant density of the p-layer have been carried out for a Au-p-n GaAs Schottky barrier cell. It is shown that AMO efficiency around 22% can be achieved in the proposed solar cell when N_D = 10¹⁶ cm^?3, N_A = 8 × 10¹⁸ cm^?3 and $\text{W}{}_{\mathrm{p}}\text{= 100}\text{A}\text{?}$ are chosen.     

Influence of inhomogeneous contact in electrical properties of 4H–SiC based Schottky diode

Schottky diodes realized on 4H–SiC n-type wafers with an epitaxial layer and a metal-oxide overlap for electric field termination were studied. The oxide was grown by plasma enhanced chemical vapor deposition (PECVD) and the Schottky barriers were formed by thermal evaporation of titanium or nickel. Diodes, with voltage breakdown as high as 700 V and ideality factor as low as 1.05, were obtained and characterized after packaging in standard commercial package (TO220).The electrical properties such as ideality factor, hight barrier, the series resistance R_s were deduced by current/voltage (I–V) analysis using the least mean square (LMS) method. The temperature effect on break voltage, R_s and saturation current was studied. A model based on two parallel Schottky diodes with two barrier heights is presented for some devices having an inhomogeneous contact. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. We use the two series RC components electrical model in order to study the dynamic behaviour of the Schottky diode in low frequency and to improve the effect of barrier inhomogeneities in electrical properties.     

InP Schottky contacts with increased barrier height

We present an analysis of Schottky barriers in n-InP made by incorporating a thin native oxide. An oxidation technique using nitric acid under illumination produces an oxide layer with uniform composition distribution within the layer. The growth rate is interpreted as being partially limited by diffusion presumably of oxygen through oxide. The Au Schottky barrier formed on a 40–80 Å thick oxide layer exhibits little degradation of the ideality factor n (1.04 < n < 1.10) and an increase of the barrier height by greater than 0.3 eV, resulting in at least a 10^?4 times smaller reverse leakage current density, compared with conventional Au-InP barriers. The barrier height increase is analysed by a generalised model, and is found to be produced by the existence of fixed negative charges in the oxide layer. From the present analysis, a surface state density of 6.0 × 10¹² cm^?2 eV^?1 and an equivalent surface density of negative charges of 2.8 × 10¹² cm^?2 are determined independently. The origins of these, particularly of the surface states, are considered in relation to the P vacancies at the oxide-InP interface.     

Role of Schottky barrier height at source/drain contact for electrical improvement in high carrier concentration amorphous InGaZnO thin film transistors

We report the fabrication of bottom-gate thin film transistors (TFTs) at various carrier concentrations of an amorphous InGaZnO (a-IGZO) active layer from ~10¹⁶ to ~10¹⁹ cm⁻³, which exceeds the limit of the concentration range for a conventional active layer in a TFT. Using the Schottky TFTs configuration yielded high TFT performance with saturation mobility (μ_sat), threshold voltage (V_TH), and on off current ratio (I_ON/I_OFF) of 16.1 cm²/V s, −1.22 V, and 1.3×10⁸, respectively, at the highest carrier concentration active layer of 10¹⁹ cm⁻³. Other carrier concentrations (<10¹⁹ cm⁻³) of IGZO resulted in a decrease of its work function and increase in activation energy, which changes the source/drain (S/D) contact with the active layer behavior from Schottky to quasi Ohmic, resulting in achieving conventional TFT. Hence, we successfully manipulate the barrier height between the active layer and the S/D contact by changing the carrier concentration of the active layer. Since the performance of this Schottky type TFT yielded favorable results, it is feasible to explore other high carrier concentration ternary and quaternary materials as active layers.