Structural and electrical properties of Au and Ti/Au contacts to n-type GaN

Au and Ti/Au layers were deposited on n-GaN. The samples were annealed at 400, 700 and 900 °C for 10 min in vacuum. The contacts were rectifying up to 700 °C and the highest Schottky barrier height of 1.07 eV was obtained for an Au single layer by current-voltage measurements. A binary phase of Au₂Ga was identified at the interface of the n-GaN/Ti/Au contact after annealing at 900 °C. The formation of Ti₂N and TiN (twin) phases epitaxially grown on GaN was also observed in the same contact as well as some gold diffusion into the topmost region of the GaN epilayer.     

Effect of annealing temperature on ZnO:Al/p-Si heterojunctions

Al-doped, zinc oxide (ZnO:Al) films with a 1.2 at.% Al concentration were deposited on p-type silicon wafers using a sol-gel dip coating technique to produce a ZnO:Al/p-Si heterojunction. Following deposition and subsequent drying processes, the films were annealed in vacuum at five different temperatures between 550 and 900 °C for 1 h. The resistivity of the films decreased with increasing annealing temperature, and an annealing temperature of 700 °C provided controlled current flow through the ZnO:Al/p-Si heterojunction up to 20 V. The ZnO:Al film deposited on a p-type silicon wafer with 1.2 at.% Al concentration was concluded to have the potential for use in electronic devices as a diode after annealing at 700 °C.     

Junction like behavior in polycrystalline diamond films

We have successfully fabricated polycrystalline diamond rectifying junction devices on n-type (1 0 0) silicon substrates by Hot Filament Chemical Vapor Deposition (HFCVD) using methane/hydrogen process gas and trimethyl borate and trimethyl phosphite dissolved in acetone as p- and n-type dopants, respectively. Impedance spectroscopy and current-voltage analysis indicates that the conduction is vertical down the grains and facets and not due to surface effects. Electrical characteristics were analyzed with In and Ti/Au top metal contacts with Al as the substrate contact. Current-voltage characteristics as a function of temperature showed barrier potentials of 1.1 eV and 0.77 eV for the In and Ti/Au contacts, respectively. Barrier heights of 4.8 eV (In) and 4.4 eV (Ti/Au) were obtained from capacitance-voltage measurements.     

Bilayer Cr/Au contacts on n-GaN

Cr/Au (40/65 nm) metal layers have been deposited by thermal evaporation onto n-GaN epitaxial layers grown by metal-organic chemical-vapour deposition (MOCVD) on a sapphire substrate. The samples have been annealed at 400, 700 and 900 °C for 10 min in vacuum. Techniques of TEM, EDS, HRTEM, FESEM, XRD and I-V characteristics have been used to characterize the micro-, and nanostructure, morphology, composition and electrical properties of the contacts before and after annealing. A binary phase of Cr₃Ga₄ and Au₇Ga₂ were identified at the interface of the n-GaN/Cr/Au contacts after annealing in vacuum at 700 and 900 °C. Current-voltage characterizations showed that the as-deposited and annealed Cr/Au contacts are rectifying up to 600 °C. After heat treatment in vacuum at 700 °C and 900 °C the Cr/Au contacts were linear.     

Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration–in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 °C, 800 °C and 900 °C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700 °C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800 °C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700 °C to parabolic law at 900 °C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900 °C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.     

Effect of annealing temperature on electrical properties of Au/polyvinyl alcohol/n-InP Schottky barrier structure

In the present work, thin film of polyvinyl alcohol (PVA) is fabricated on n-type InP substrate as an interfacial layer for electronic modification of Au/n-InP Schottky contact. The electrical characteristics of Au/PVA/n-InP Schottky diode are determined at annealing temperature in the range of 100-300 °C by current-voltage (I-V) and capacitance-voltage (C-V) methods. The Schottky barrier height and ideality factor (n) values of the as-deposited Au/PVA/n-InP diode are obtained at room temperature as 0.66 eV (I-V), 0.82 eV (C-V) and 1.32, respectively. Upon annealing at 200 °C in nitrogen atmosphere for 1 min, the barrier height value increases to 0.81 eV (I-V), 0.99 eV (C-V) and ideality factor decreases to 1.18. When the contact is annealed at 300 °C, the barrier height value decreases to 0.77 eV (I-V), 0.96 eV (C-V) and ideality factor increases to 1.22. It is observed that the interfacial layer of PVA increases the barrier height by the influence of the space charge region of the Au/n-InP Schottky junction. The discrepancy between Schottky barrier heights calculated from I-V and C-V measurements is also explained. Further, Cheung's functions are used to extract the series resistance of Au/PVA/n-InP Schottky diode. The interface state density as determined by Terman's method is found to be 1.04 × 10¹² and 0.59 × 10¹² cm^− 2 eV^− 1 for the as-deposited and 200 °C annealed Au/PVA/n-InP Schottky diodes. Finally, it is seen that the Schottky diode parameters changed with increase in the annealing temperature.     

Influence of rapid thermal annealing effect on electrical and structural properties of Pd/Ru Schottky contacts to n-type GaN

Pd/Ru metallization scheme is fabricated on n-GaN as a Schottky contact, and the electrical and structural properties have been investigated as a function of annealing temperature by current–voltage (I–V), capacitance–voltage (C–V), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements. As-deposited Ru/Pd/n-GaN contact yielded Schottky barrier height (SBH) of 0.67 eV (I–V) and 0.79 eV (C–V), respectively. Further, it is observed that the Schottky barrier height increases to 0.80 eV (I–V) and 0.96 eV (C–V) for the contact annealed at 300 °C. However, both I–V and C–V measurements indicate that the barrier height slightly decreased when the contacts are annealed at 400 °C and 500 °C. From the above observations, the optimum annealing temperature for Pd/Ru Schottky contact is 300 °C. Norde method is also employed to extract the barrier height of Pd/Ru Schottky contacts which are in good agreement with those obtained by the I–V technique. X-ray photoelectron spectroscopy results shows that the Ga 2p core-level shift towards the low-energy side for the contact annealed at 300 °C compared to the as-deposited contact. Based on the XPS and XRD results, the reason for the increase in SBH upon annealing at 300 °C could be attributed to the formation of gallide phases at the Ru/Pd/n-GaN interface vicinity. The AFM results showed that the overall surface morphology of the Pd/Ru Schottky contacts on n-GaN is fairly smooth. The above observations reveal that the Pd/Ru Schottky contact is attractive for high-temperature device applications.     

Thermal stability of undoped polycrystalline silicon layers on antimony and boron-doped substrates

The structure of as-deposited and annealed polycrystalline silicon layers has been investigated by scanning electron microscopy and x-ray diffraction. The structure of intentionally undoped layers prepared by low pressure chemical vapor deposition at a temperature of 640 °C was found to be stable upon annealing at temperatures lower than about 900 °C. On the other hand, primary recrystallization of the layers has been observed during annealing at temperatures in the range of 900 to 1150 °C. Isochronal annealing revealed the activation energy for the primary recrystallization of undoped layers as 0.6 eV. The activation energy for diffusion of silicon self-interstitials along the grain boundaries was calculated to be 2.2 eV. The difference in grain-growth process was observed for the undoped layers grown either (i) on lightly boron-doped substrate or (ii) on the substrate heavily doped with antimony. The different grain-growth mechanism was found to be a consequence of antimony diffusion into the polycrystalline layer.     

Thermal annealing behaviour of Pd Schottky contacts on melt-grown single crystal ZnO studied by IV and CV measurements

Current-voltage (IV) and capacitance-voltage (CV) measurement techniques have successfully been employed to study the effects of annealing highly rectifying Pd/ZnO Schottky contacts. IV results reveal a decrease in the contact quality with increasing annealing temperature as confirmed by a decrease in the zero bias barrier height and an increase in the reverse current measured at −1.5 V. An average barrier height of (0.77 ± 0.02) eV has been calculated by assuming pure thermionic emission for the as-deposited material and as (0.56 ± 0.03) eV after annealing at 550 °C. The reverse current has been measured as (2.10 ± 0.01) × 10⁻¹⁰ A for the as-deposited and increases by 5 orders of magnitude after annealing at 550 °C to (1.56 ± 0.01) × 10⁻⁵ A. The depletion layer width measured at −2.0 V has shown a strong dependence on thermal annealing as it decreases from 1.09 μm after annealing at 200 °C to 0.24 μm after annealing at 500 °C, resulting in the modification of the dopant concentration within the depletion region and hence the current flowing through the interface from pure thermionic emission to thermionic field emission with the donor concentrations increasing from 6.90 × 10¹⁵ cm⁻³ at 200 °C to 6.06 × 10¹⁶ cm⁻³ after annealing at 550 °C. This increase in the volume concentration has been explained as an effect of a conductive channel that shifts closer to the surface after sample annealing. The series resistance has been observed to decrease with increase in annealing temperature. The Pd contacts have shown high stability up to an annealing temperature of 250 °C as revealed by the IV and CV characteristics after which the quality of the contacts deteriorates with increase in annealing temperature.     

Broad band optical characterization of sol-gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO₂) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO₂ thin films was studied in the range of 0.62 to 4.96 eV photon energy (250-2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol-gel precursors and the creation of dense layers of TiO₂. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol-gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.     

The interaction of Al,Ag, Au,and Ti to Pr2O3 thin film dielectrics

We studied the thermal stability of various electrode materials on 2 nm Pr₂O₃ dielectric films. Thin Al, Au, Ag, and Ti layers are deposited, by thermal evaporation or by sublimation (case of Ti). The Pr₂O₃ layers were deposited on Si substrates by electron beam evaporation from a Pr₆O₁₁ powder and by wet chemical deposition. XPS and SR-PES were used to study the effect of annealing on the metal to Pr₂O₃ interaction. XPS results show a strong diffusivity of Al, Ag, and Au in Pr₂O₃ upon annealing to 300 °C with formation of alloying with Si substrate. In contrast, Ti remained stable even upon annealing to 900 °C. SR-PES results show a stable Titanium oxides formation at room temperature. All results demonstrate that Ti is a good diffusion barrier between metal contacts and Pr₂O₃ or can be used as a metal contact.     

Physical properties of electrically conductive Sb-doped SnO2 transparent electrodes by thermal annealing dependent structural changes for photovoltaic applications

We have investigated the optical and electrical characteristics of antimony (Sb)-doped tin oxide (SnO₂) films with modified structures by thermal annealing as a transparent conductive electrode. The structural properties were analyzed from the relative void % by spectroscopic ellipsometry as well as the scanning electron microscopy images and X-ray diffraction patterns. As the annealing temperature was raised, Sb-doped SnO₂ films exhibited a slightly enhanced crystallinity with the increase of the grain size from 17.1 nm at 500 °C to 34.3 nm at 700 °C. Furthermore, the refractive index and extinction coefficient gradually decreased due to the increase in the relative void % within the film during the annealing. The resistivity decreased to 8.2 × 10⁻³ Ω cm at 500 °C, but it increased rapidly at 700 °C. After thermal annealing, the optical transmittance was significantly increased. For photovoltaic applications, the photonic flux density and the figure of merit over the entire solar spectrum were obtained, indicating the highest values of 5.4 × 10¹⁴ cm⁻² s⁻¹ nm⁻¹ at 1.85 eV after annealing at 700 °C and 340.1 μA cm⁻² Ω⁻¹ at 500 °C, respectively.     

Phase formation at rapid thermal annealing of Al/Ti/Ni ohmic contacts on 4H-SiC

Ohmic contacts to the top p-type layers of 4H-SiC p⁺–n–n⁺ epitaxial structures having an acceptor concentration lower than 1×10¹⁹ cm⁻³ were fabricated by the rapid thermal anneal of multilayer Al/Ti/Pt/Ni metal composition. The rapid thermal anneal of multilayer A1/Ti/Pt/Ni metal composition led to the formation of duplex cermet composition containing Ni₂Si and TiC phases. The decomposition of the SiC under the contact was found to be down to a depth of about 100 nm. The contacts exhibited a contact resistivity R_c of 9×10⁻⁵ Ω cm⁻² at 21°C, decreasing to 3.1×10⁻⁵ Ω cm⁻² at 186°C. It was found that thermionic emission through the barrier having a height of 0.097 eV is the predominant current transport mechanism in the fabricated contacts.     

Effects of thermal annealing on the performance of Al/ZnO nanorods/Pt structure ultraviolet photodetector

ZnO nanorod arrays were fabricated on ZnO coated glass substrate by hydrothermal method. Schottky barrier ultraviolet photodetectors (PDs) were obtained by sputtering Pt electrode and evaporating Al electrode on the top of ZnO nanorod arrays with thermal treatment. It is illustrated that Schottky contacts at the electrode/ZnO NRs interface were formed at the annealing temperature of 300 °C and above. When annealing temperature was up to 300 °C, the performance of the PDs was improved with the great decrease of response and recovery times. At the forward bias of 2 V, the Schottky contact PDs showed the biggest responsivity and the best detectivity at the annealing temperature of 300 °C. For annealing temperature at 300 °C and above, the responsivity decreases with increasing annealing temperature and the ratio of detectivity (D₂₅₄^* to D₅₄₆^*) was calculated as high as 10³ for all PDs annealed at 300 °C and above.     

The effect of high temperature annealing on Schottky diode characteristics of Au/n-Si contacts

The current-voltage and capacitance-voltage characteristics of Au/n-Si/Al Schottky barrier diode were measured in the temperature range of 100-800 °C. Au/n-Si/Al Schottky barrier diode annealed at temperatures from 100 °C to 400 °C for 5 min and from 500 °C to 800 °C for 7 min in N₂ atmosphere. The electronic parameters such as barrier height and ideality factor (n) of the device were determined using Cheung's method. To determine whether or not a Schottky diode is ideal it can be used the ideality factor (n) found from its forward current-voltage (I-V) characteristics. It has been found that the value of Φ_b (0.82 or 0.83 eV) remains constant up to 500 °C and 0.80 and 0.79 eV in 600, 750 °C respectively in the forward I-V mode. An ideality factor value of 1.04 was obtained for as-deposited sample. The ideality factor n varied from 1.04 to 2.30. The experimental results have shown that the ideality factor (n) values increases with increasing annealing temperature up to 750 °C. This has been explained in terms of the presence of different metallic-like phases produced by chemical reactions between the Au and Si substrate because of the annealing process. The Φ_b (C-V) values obtained from the reverse-bias C⁻²-V curves of the as-deposited and annealed diode are in the range 0.99-1.12 eV. The difference between Φ_b (C-V) and the Φ_b (I-V) is in close agreement with values reported in literature. Besides Fermi energy level and carrier concentration determined by using thermionic emission (TE) mechanism show strong temperature dependence. It has been seen current-voltage characteristics of the diode show an ideal behavior.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

Low-resistance and highly transparent Ag/IZO ohmic contact to p-type GaN

The electrical, structural, and optical characteristics of Ag/ZnO-doped In₂O₃ (IZO) ohmic contacts to p-type GaN:Mg (2.5 × 10¹⁷ cm^− 3) were investigated. The Ag and IZO (10 nm/50 nm) layers were prepared by thermal evaporation and linear facing target sputtering, respectively. Although the as-deposited and 400 °C annealed samples showed rectifying behavior, the 500 and 600 °C annealed samples showed linear I-V characteristics indicative of the formation of an ohmic contact. The annealing of the contact at 600 °C for 3 min in a vacuum (~ 10^− 3 Torr) resulted in the lowest specific contact resistivity of 1.8 × 10^− 4 Ω·cm² and high transparency of 78% at a wavelength of 470 nm. Using Auger electron spectroscopy, depth profiling and synchrotron X-ray scattering analysis, we suggested a possible mechanism to explain the annealing dependence of the electrical properties of the Ag/IZO contacts.     

Micro-hardness, microstructures and thermal stability of (Ti,Cr,Al,Si)N films deposited by cathodic arc method

(Ti,Cr,Al,Si)N films were deposited by cathodic arc method using TiCrAlSi alloy cathodes. It was found that the microstructures of (Ti,Cr,Al,Si)N were closely related to (Al+Si) content. The crystal structure of (Ti,Cr,Al,Si)N was NaCl-type structure up to the (Al+Si) content of 0.60, where it changed to a hexagonal structure. The maximum hardness of 33 GPa was obtained at the lowest (Al+Si) content of 0.56, still in the cubic structure. The micro-hardness decreased down to 28 GPa as the crystal structure changed from NaCl-type to wurtzite-type.To investigate the thermal stabilities of (Ti,Cr,Al,Si)N, the films were annealed in a vacuum furnace. In Ti_0.20Cr_0.20Al_0.55Si_0.05N with cubic structure, the phase segregation occurred by annealing at over 900 °C, while Ti_0.22Cr_0.22Al_0.44Si_0.12N remained in cubic phase up to 1000 °C. The micro-hardness of Ti_0.20Cr_0.20Al_0.55Si_0.05N increased and that of Ti_0.22Cr_0.22Al_0.44Si_0.12N decreased at 1000 °C. Ti_0.20Cr_0.11Al_0.58Si_0.11N with a cubic and hexagonal mixture phase held its (c,h)-mixture phase up to 1000 °C, while there was an indication of an increase both in micro-hardness and in cubic ratio after annealing.In this paper, the micro-hardness and microstructure of (Ti,Cr,Al,Si)N are discussed as a function of annealing temperature and investigated by X-ray diffraction and electron microscopy.     

Analysis of current-voltage and capacitance-voltage-frequency characteristics in Al/p-Si Schottky diode with the polythiophene-SiO2 nanocomposite interfacial layer

The current-voltage characteristic of the prepared Al/Polythiophene-SiO₂/p-Si Schottky diode was analyzed by using different methods at room temperature. The barrier height and ideality factor of the diode were determined by using the conventional current-voltage method as 0.729 eV and 2.12, respectively. The barrier height values calculated by means of the modified Norde functions have showed good agreement with the barrier height value obtained by using the current-voltage method. The series resistance which causes the electrical characteristics to be non-ideal was calculated from Cheung functions and the modified Norde functions. The energy distribution of the interface states has been determined from the forward-bias current-voltage data. The frequency dependence of the Schottky diode parameters obtained from capacitance-voltage characteristics has been analyzed.     

Thickness dependence of microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Ag underlayer (30 nm) has improved the degree of ordering and perpendicular magnetic anisotropy of CoPt films (7.5-10 nm). After annealing at 600 °C and 700 °C, the perpendicular coercivity of CoPt/Ag films has been raised as the thicknesses of CoPt layers are increased. The magnetic easy axis of CoPt/Ag films would change from a random orientation to an out-of-plane orientation. It is found that Ag underlayer with thickness of 30 nm can improve the perpendicular magnetic properties of CoPt layers with thicknesses in the range of 7.5-10 nm. The CoPt/Ag films would be a candidate for perpendicular magnetic recording media.