Series resistance calculation for Ag contacts on single crystal layered p-SnS and p-SnSe compound semiconductors in the wide temperature range

This paper summarizes the first results of characteristics parameters obtained from current-voltage (I-V) measurements for Ag/p-SnS and Ag/p-SnSe structure. The reverse and forward bias current-voltage characteristics of Ag Schottky contacts on a Bridgman-Stockbarger grown p-SnS and p-SnSe layered semiconducting material have been measured at various temperatures. We have tried to determine contact properties such as apparent barrier heights Φ_B0, ideality factor n and series resistance R_s. The apparent barrier height and ideality factor calculated by using thermionic emission theory were found to be strongly temperature dependent. Evaluating forward I-V data reveals a decrease at the apparent barrier height, but an increase at the ideality factor with decrease in temperature. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature dependent and decreased with increasing temperature. It has been found that both contacts are of Schottky type.     

Schottky barrier height variation with metallurgical reactions in aluminum-titanium-gallium arsenide contacts

The behaviour of A1/Ti/n-GaAs Schottky contacts under heat treatment at around 400°C have been studied for their application to GaAs MESFETs. Barrier heights have been determined using both I-V and C-V measurements as a function of heat treatment time. Reaction products due to heat treatment have been studied by X-ray diffraction and Auger electron spectroscopy. The A1/Ti/n-GaAs Schottky contacts barrier height shows an $\text{“N”-}\text{shaped}$ variation in response to heat treatment time. A marked reduction in barrier height follows a slight increase at the initial annealing stage. The barrier height then takes a minimum value. The slight increase in barrier height at the initial stage in the heat treatment is brought about by a Ti and GaAs reaction. The marked barrier height reduction is closely correlated to formation of the compound Al₃Ti. The increase in barrier height observed after the reduction can be explained in terms of GaAlAs formation at the metal-semiconductor interface. This seems to indicate that heat treatment is essential for application of Al/Tin-GaAs Schottky contacts to practical devices.     

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.     

The contact of metal with silicon carbide: Schottky barrier height in relation to SiC polytype

The results obtained in measuring the Schottky barrier height Φ _b ⁿ for a chromium contact with 8H-, 6H-, 15R-, 27R-and 4H-SiC silicon carbide polytypes with n-type conduction are analyzed in terms of a simple model. It is shown that the Φ _b ⁿ value is proportional to the concentration of silicon vacancies in the polytypes. The results of Φ _b ⁿ measurements for palladium and platinum contacts to silicon carbide polytypes are discussed.     

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.     

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.     

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.     

Schottky barrier height of sputtered TiN contacts on silicon

The Schottky barrier height of sputtered TiN on both p- and n-type silicon was determined by I-V and C-V measurements. The barrier height is found to increase on n-Si and to decrease on p-Si, upon thermal annealing. The experimental results are explained in terms of sputtering damage. This damage is modeled by donor-like traps whose concentration decays exponentially from the silicon surface. A characteristic length equal to 45 Å accounts for the observed characteristics. The trap-free values of the barrier height were obtained by I-V measurements after sequential thermal annealing up to 600°C. These values are φ_Bn = 0.55 V on n-type and φ_Bp = 0.57 V on p-type silicon.     

Metallurgical and electrical properties of chromium silicon interfaces

The effect of annealing treatment up to 500°C on CrSi contacts was studied from physico-chemical and electrical view points. The solid-solid reactions between a 1000 Å thick Cr layer and a 〈111〉N single crystal of silicon, were studied by the He⁺ ion backscattering method, X-ray diffraction and transmission electron microscopy. We first observed a growth in the Cr grains and then the nucleation and growth of the disilicide CrSi₂. For annealing temperatures greater than 415°C, the growth is linear in time with an activation energy of 1.5±0.1 eV and for lower temperatures it becomes superlinear. The growth mechanism is discussed in terms of growth limiting phenomena. The variations of the electrical parameters (ideality factor n and barrier height 0_Bn) as a function of 15 min anneals between 300 and 500°C were correlated to the physico chemical observations. We establish, firstly, an optimal temperature annealing range in order to obtain good Schottky CrSi diodes and, secondly, a low limit of Cr thickness which must be deposited to obtain acceptable Schottky CrSi₂  Si diodes after annealing.     

Studies of Ti- and Ni-germanide Schottky contacts on n-Ge(1 0 0) substrates

In this study, we investigated fabrication and characteristics of germanides Schottky contacts on germanium. Ti- and Ni-germanides were fabricated on n-Ge(1 0 0) substrates by sputtering metal Ti or Ni on Ge followed by a furnace annealing. The influence of annealing temperature on the electrical properties of Ti- and Ni-germanide on n-Ge(1 0 0) substrates was investigated. The low temperature ∼300 °C annealing helped to obtain the optimized Schottky contact characteristics in both Ti-germanide/Ge and Ni-germanide/Ge substrates contacts. The well-behaved Ti-germanides/n-Ge Schottky contact with 0.34 eV barrier height was obtained by using a 300 °C annealing process.     

Characteristics of metal-semiconductor contacts fabricated by the electroless deposition method

Metal-semiconductor contacts have been fabricated by electroless deposition of Cu on chemically cleaned n-type silicon and their characteristics studied. The values of barrier height and the ideality factor are found to be comparable to those of vacuum evaporated contacts. A non-linearity in the 1/C² vs V plot has been observed and the same has been satisfactorily explained by taking surface state capacitance into consideration.     

Current diffusion effects in titanium-N silicon schottky diodes

Measurements of the reverse current-voltage characteristics of titanium-n silicon Schottky barrier diodes are presented which demonstrate that diffusion limited currents can occur in these diodes when the internal electric field is low. For the titanium-n silicon diodes, the low barrier height of 0.51 eV and doping concentration of 10¹⁵ cm^?3 result in an electric field of 8 × 10³ V cm^?1 at zero bias. An observed decrease in the reverse saturation current at low bias, previously described as anomalous, is now reconciled with the thermionic-diffusion theory of current flow, whoch predicts a reduction in A⁷, the effective Richardson constant, at internal fields below 10⁵ V cm^?1.     

Control of charge transport mode in the Schottky barrier by δ-doping: Calculation and experiment for Al/GaAs

The possibility of controlling the effective barrier height in Schottky diodes by introducing a δ-doped layer near the metal-semiconductor contact is considered. A decrease in the effective barrier height is caused by the increased role of carrier tunneling through the barrier. A complete quantum-mechanical numerical simulation of the effect of the δ-layer parameters (concentration and depth) on the current-voltage characteristics of modified diodes was carried out for the Schottky barrier contacts to n-GaAs. The simulation results were found to fit well the experimental characteristics of diodes produced by metal-organic chemical vapor epitaxy. The studies carried out made it possible to choose the optimal δ-layer parameters to produce low-barrier (about 0.2 eV) diodes with a reasonable nonideality factor (n≤1.5). Such structures can be employed to fabricate microwave detector diodes without bias.     

Ta/Si Schottky diodes fabricated by magnetron sputtering technique

Electrical properties of Ta/n-Si and Ta/p-Si Schottky barrier diodes obtained by sputtering of tantalum (Ta) metal on semiconductors have been investigated. The characteristic parameters of these contacts like barrier height, ideality factor and series resistance have been calculated using current voltage (I-V) measurements. It has seen that the diodes have ideality factors more than unity and the sum of their barrier heights is 1.21 eV which is higher than the band gap of the silicon (1.12 eV). The results have been attributed the effects of inhomogeneities at the interface of the devices and native oxide layer. In addition, the barrier height values determined using capacitance-voltage (C-V) measurements have been compared the ones obtained from I-V measurements. It has seen that the interface states have strong effects on electrical properties of the diodes such as C-V and R_s-V measurements.     

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.     

Metal-semiconductor contacts to n-ZnS0.07Se0.93

A systematic study was conducted on electrical properties of metal-semiconductor contacts to n-ZnS_0.07Se_0.93 with metals of different metal work functions. A clear relation was found between the Schottky barrier height and the metal work function although the Schottky contact theory could not predict it accurately. Thermionic-emission was found to be the dominant current transport mechanism. A significant Schottky barrier height improvement was achieved by means of a cryogenic process technique for forming the Au/n-ZnS_0.07Se_0.93 contact. A thermal stability study was also conducted on Pd and Au/n-ZnS_0.07Se_0.93 contacts. Thermal annealing tests showed a stable electrical property up to T = 250°C for the Pd contact and T = 150°C for the Au contact, however, a dramatic degradation was observed after higher temperature annealing and this is attributed to the interaction between metals and ZnSSe after annealing as supported by Auger electron spectroscopy.     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

Influence of annealing on the metal/semiconductor contacts deposited on sulfur-treated <Emphasis Type="Italic">n</Emphasis>-GaAs surface

Comparative analysis of the influence of thermal annealing on Ge/Au/Ni-, Ge/Au/Ti/Au-, and Ge/Au/Ni/Ti/Au-based ohmic contacts and Ti/Au-based Schottky contacts deposited on an n-GaAs (100) surface treated and nontreated in (NH₄)₂S aqueous solution have been performed. Annealing conditions for ohmic contacts are found that lead to a decrease in the specific contact resistance of sulfur-treated samples by a factor of 2.5–15 in comparison with the nontreated samples. Optimal annealing conditions are also determined for sulfur-treated GaAs samples with Schottky contacts, which make it possible to reduce the ideality factor and increase the barrier height and the breakdown voltage with respect to the nontreated samples.     

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.     

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.