The effects of annealing on Au/pyronine-B/MD n-InP Schottky structure

Thin film of non-polymeric organic compound pyronine-B has been fabricated on moderately doped (MD) n-InP substrate as an interfacial layer using spin coating technique for the electronic modification of Au/MD n-InP Schottky contact. The electrical characteristics have been determined at room temperature. The barrier height and the ideality factor values for Au/pyronine-B/MD n-InP Schottky diode have been obtained from the forward bias I-V characteristics at room temperature as 0.60 eV and 1.041; 0.571 and 1.253 eV after annealing at 100 and 250 °C, respectively. An increase in annealing temperature at the Au/n-InP Schottky junction is shown to increase the reverse bias leakage current by about one order of magnitude and decrease the Schottky barrier height by 0.027 eV. Furthermore, the barrier height values for the Au/pyronine-B/MD n-InP Schottky diode have also been obtained from the C-V characteristics at room temperature as 1.001 and 0.709 eV after annealing at 100 and 250 °C, respectively. Finally, it was seen that the diode parameters changed with increase in the annealing temperature.     

Annealing and measurement temperature dependence of W2B5-based rectifying contacts to n-GaN

The thermal stability and measurement temperature dependence of Schottky contact characteristics on n-GaN using a W₂B₅/Ti/Au metallization scheme was studied using current-voltage (I-V), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) measurements. The elemental profile obtained from samples annealed at 350 °C showed some titanium diffusion into the gold layer but little other difference from the as-deposited wafer. Annealing at 700 °C produced significant diffusion of titanium. The Schottky barrier height increased with anneal temperature up to 200 °C, reaching a maximum value of 0.65 eV, but decreased at higher annealing temperatures. The reverse breakdown voltage from diodes fabricated using the W₂B₅-based contacts showed a similar dependence. The reverse current magnitude was larger than predicted by thermionic emission alone. The barrier height showed only minor changes with measurement temperature up to 150 °C.     

Magnetic properties and microstructure study of high coercivity Au/FePt/Au trilayer thin films

High-coercivity Au(60 nm)/FePt(δ nm)/Au(60 nm) trilayer samples were prepared by sputtering at room temperature, followed by post annealing at different temperatures. For the sample with δ=60 nm, L1₀ ordering transformation occurs at 500 °C. Coercivity (H_c) is increased with the annealing temperature in the studied range 400–800 °C. The H_c value of the trilayer films is also varied with thickness of FePt intermediate layer (δ), from 27 kOe for δ=60 nm to a maximum value of 33.5 kOe for δ=20 nm. X-ray diffraction data indicate that the diffusion of Au atoms into the FePt L1₀ lattice is negligible even after a high-temperature (800 °C) annealing process. Furthermore, ordering parameter is almost unchanged as δ is reduced from 60 to 15 nm. Transmission electron microscope (TEM) photos indicate that small FePt Ll₀ particles are dispersed amid the large-grained Au. We believe that the high coercivity of the trilayer sample is attributed to the small and uniform grain sizes of the highly ordered FePt particles which have perfect phase separation with Au matrix.     

Electrical characterisation of ruthenium Schottky contacts on n-Ge (1 0 0)

Ruthenium (Ru) Schottky contacts were fabricated on n-Ge (1 0 0) by electron beam deposition. Current–voltage (I–V), deep level transient spectroscopy (DLTS), and Laplace-DLTS techniques were used to characterise the as-deposited and annealed Ru/n-Ge (1 0 0) Schottky contacts. The variation of the electrical properties of the Ru samples annealed between 25 °C and 575 °C indicates the formation of two phases of ruthenium germanide. After Ru Schottky contacts fabrication, an electron trap at 0.38 eV below the conduction band with capture cross section of 1.0×10⁻¹⁴ cm⁻² is the only detectable electron trap. The hole traps at 0.09, 0.15, 0.27 and 0.30 eV above the valence band with capture cross sections of 7.8×10⁻¹³ cm⁻², 7.1×10⁻¹³ cm⁻², 2.4×10⁻¹³ cm⁻² and 6.2×10⁻¹³ cm⁻², respectively, were observed in the as-deposited Ru Schottky contacts. The hole trap H(0.30) is the prominent single acceptor level of the E-centre, and H(0.09) is the third charge state of the E-centre. H(0.27) shows some reverse annealing and reaches a maximum concentration at 225 °C and anneals out after 350 °C. This trap is strongly believed to be V–Sb₂ complex formed from the annealing of V–Sb defect centre.     

ZrB2-based Ohmic contacts to p-GaN

The annealing temperature dependence of contact resistance and layer stability of ZrB₂/Ti/Au and Ni/Au/ZrB₂/Ti/Au Ohmic contacts on p-GaN is reported. The as-deposited contacts are rectifying and transition to Ohmic behavior for annealing at ≥750 °C, a significant improvement in thermal stability compared to the conventional Ni/Au Ohmic contact on p-GaN, which is stable only to <600 °C. A minimum specific contact resistance of ∼2 × 10⁻³ Ω cm⁻² was obtained for the ZrB₂/Ti/Au after annealing at 800 °C while for Ni/Au/ZrB₂/Ti/Au the minimum value was 10⁻⁴ Ω cm⁻² at 900 °C. Auger Electron Spectroscopy profiling showed significant Ti, Ni and Zr out diffusion at 750 °C in the Ni/Au/ZrB₂/Ti/Au while the Ti and Zr intermix at 900 °C in the ZrB₂/Ti/Au. These boride-based contacts show promise for contacts to p-GaN in high temperature applications.     

Effect of thermal annealing on ohmic contacts properties of undoped and Si-doped AlxGa1−xN on Si (1 1 1) substrate grown by PA-MBE

In this work, we study the ohmic contact properties of titanium (Ti)/aluminum (Al) bi-layer contacts on undoped and n-type doped Al_xGa_1−xN grown on silicon (1 1 1) substrates by radio frequency nitrogen plasma-assisted molecular beam epitaxy (PA-MBE). The electrical stability of the contacts at various annealing temperatures of 400, 500, 600 and 700 °C were investigated. Specific contact resistivity was determined using transmission line method (TLM) and current–voltage (I–V) measurements. The results reveal that the bi-layer scheme was sensitive to the change of annealing temperatures and annealing time. The optimal value of specific contact resistivities was obtained at annealing temperature of 600 °C for both samples. However, the values of n-type doped sample exhibited better results compared with the undoped sample.     

Effects of post-thermal annealing temperature on the optical and structural properties of gold particles on silicon suboxide films

In this work, silicon suboxide (SiO_x) thin films were deposited using a RF magnetron sputtering system. A thin layer of gold (Au) with a thickness of about 10 nm was sputtered onto the surface of the deposited SiO_x films prior to the thermal annealing process at 400 °C, 600 °C, 800 °C and 1000 °C. The optical and structural properties of the samples were studied using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and optical transmission and reflection spectroscopy. SEM analyses demonstrated that the samples annealed at different temperatures produced different Au particle sizes and shapes. SiO_x nanowires were found in the sample annealed at 1000 °C. Au particles induce the crystallinity of SiO_x thin films in the post-thermal annealing process at different temperatures. These annealed samples produced silicon nanocrystallites with sizes of less than 4 nm, and the Au nanocrystallite sizes were in the range of 7-23 nm. With increased annealing temperature, the bond angle of the Si-O bond increased and the optical energy gap of the thin films decreased. The appearance of broad surface plasmon resonance absorption peaks in the region of 590-740 nm was observed due to the inclusion of Au particles in the samples. The results show that the position and intensity of the surface plasmon resonance peaks can be greatly influenced by the size, shape and distribution of Au particles.     

Thermal stability of Ti/Al/Pt/Au and Ti/Au Ohmic contacts on n-type ZnCdO

The specific contact resistivity and chemical intermixing of Ti/Au and Ti/Al/Pt/Au Ohmic contacts on n-type Zn_0.05Cd_0.95O layers grown on ZnO buffer layers on GaN/sapphire templates is reported as a function of annealing temperature in the range 200-600 °C. A minimum contact resistivity of 2.3 × 10⁻⁴ Ω cm² was obtained at 500 °C for Ti/Al/Pt/Au and 1.6 × 10⁻⁴ Ω cm² was obtained at 450 °C for Ti/Al. These values also correspond to the minima in transfer resistance for the contacts. The Ti/Al/Pt/Au contacts show far smoother morphologies after annealing even at 600 °C, whereas the Ti/Au contacts show a reacted appearance after 350 °C anneals. In the former case, Pt and Al outdiffusion is significant at 450 °C, whereas in the latter case the onset of Ti and Zn outdiffusion is evident at the same temperature. The improvement in contact resistance with annealing is suggested to occur through formation of TiO_x phases that induce oxygen vacancies in the ZnCdO.     

Use of TiB2 diffusion barriers for Ni/Au ohmic contacts on p-GaN

The use of a TiB₂ diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25-950 °C) dependence of ohmic contact characteristics using a Ni/Au/TiB₂/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500 °C . A minimum specific contact resistivity of ∼3 × 10⁻⁴ Ω cm⁻² was obtained after annealing over a broad range of temperatures (800-950 °C for 60 s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB₂ at 800 °C. By 900 °C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB₂ diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500 °C.     

Thermal annealing effect on the crystallization and optical dispersion of sprayed V2O5 thin films

Polycrystalline vanadium pentoxide (V₂O₅) thin films have been deposited by spray pyrolysis technique on preheated glass substrate. The influence of thermal annealing on the crystallization of V₂O₅ has been investigated. X-ray diffraction analysis (XRD) revealed that the films deposited at T_sub=350 °C were orthorhombic structures with a preferential orientation along 〈0 0 1〉 direction. Moreover, the degree of crystallinity was improved by thermal annealing. Optical properties of these samples were studied by spectrophotometer in the wavelength range 300-2500 nm. Some of the important optical absorptions such as optical dispersion energies E_o and E_d, dielectric constant ε, ratio between number of charge carriers and effective mass N/m^*, wavelength of single oscillator λ₀, plasma frequency ω_p, single resonant frequency ω₀ and the average of oscillator strength S_o, have been evaluated. In the annealing process, the dielectric properties have weak dependencies of film thickness and annealing time. Furthermore, a value of carrier concentration was obtained of 3.02×10²⁵ m⁻³ for the as-deposited film and slight changes with annealing time.     

Electrical, structural and surface morphological properties of thermally stable low-resistance W/Ti/Au multilayer ohmic contacts to n-type GaN

A W/Ti/Au multilayer scheme has been fabricated for achieving thermally stable low-resistance ohmic contact to n-type GaN (4.0 × 10¹⁸ cm⁻³). It is shown that the as-deposited W/Ti/Au contact exhibits near linear I-V behaviour. However, annealing at temperature below 800 °C the contacts exhibit non-linear behaviour. After annealing at a temperature in excess of 850 °C, the W/Ti/Au contact showed ohmic behaviour. The W/Ti/Au contact produced specific contact resistance as low as 6.7 × 10⁻⁶ Ω cm² after annealing at 900 °C for 1 min in a N₂ ambient. It is noted that the specific contact resistance decreases with increase in annealing temperature. It is also noted that annealing the contacts at 900 °C for 30 min causes insignificant degradation of the electrical and thermal properties. It is further shown that the overall surface morphology of the W/Ti/Au stayed fairly smooth even after annealing at 900 °C. The W/Ti/Au ohmic contact showed good edge sharpness after annealing at 900 °C for 30 min. Based on the Auger electron spectroscopy and glancing angle X-ray diffraction results, possible explanation for the annealing dependence of the specific contact resistance of the W/Ti/Au contacts are described and discussed.     

Influence of heat treatment on the structure and magnetic properties of the Co/Zr and Co/Hf multilayer amorphous films

The influence of annealing on the structure and magnetic properties of amorphous Co/Zr and Co/Hf multilayer films was studied with particular attention to the dependence of the magnetic properties, thermal stability and crystallization process on layer composition and thickness. The temperature at which crystallization commences increases from 400 to 460 °C as the layer thickness d_Zr or d_Hf increases from 6 to 18 Å, and decreases from 450 to 400 °C as d_Co increases from 12 to 18 Å. Multilayers containing 19–60 at% Zr were studied. The specific magnetization was found to increase even below the temperature at which crystallization commences. Our data are compared with non-multilayer Co–Zr amorphous films and rapidly quenched metallic glasses.     

Annealing effects on structural, optical and electrical properties of e-beam evaporated CuIn0.5Ga0.5Te2 thin films

CuIn_0.5Ga_0.5Te₂ (CIGT) thin films have been prepared by e-beam evaporation from a single crystal powder synthesized by direct reaction of constituent elements in a stoichiometric proportion. Post-depositional annealing has been carried out at 300 and 350 °C. The compositions of the films were determined by energy dispersive X-ray analysis (EDXA) and it was found that there was a remarkable fluctuation in atomic percentage of the constituent elements following to the post-depositional annealing. X-ray diffraction analysis (XRD) has shown that as-grown films were amorphous in nature and turned into polycrystalline structure following to the annealing at 300 °C. The main peaks of CuIn_0.5Ga_0.5Te₂ and some minor peaks belonged to a binary phase Cu₂Te appeared after annealing at 300 °C, whereas for the films annealed at 350 °C single phase of the CuIn_0.5Ga_0.5Te₂ chalcopyrite structure was observed with the preferred orientation along the (1 1 2) plane. The effect of annealing on and near surface regions has been studied using X-ray photoelectron spectroscopy (XPS). The results indicated that there was a considerable variation in surface composition following to the annealing process. The transmission and reflection measurements have been carried out in the wavelength range of 200-1100 nm. The absorption coefficients of the films were found to be in the order of 10⁴ cm⁻¹ and optical band gaps were determined as 1.39, 1.43 and 1.47 eV for as-grown and films annealed at 300 and 350 °C, respectively. The temperature dependent conductivity and photoconductivity measurements have been performed in the temperature range of −73 to 157 °C and the room temperature resistivities were found to be around 3.4 × 10⁷ and 9.6 × 10⁶ (Ω cm) for the as-grown and annealed films at 350 °C, respectively.     

C-V analysis of rapidly thermal annealed SF6 plasma treated AlGaN/GaN heterostructures

We studied influence of rapid thermal annealing on electrical parameters of SF₆ plasma treated AlGaN/GaN heterostructures. The main emphasis by the evaluation was laid on C-V measurement and simulation, but also I-V and SIMS measurement were used. It was found that the diminished sheet carrier concentration of a two-dimensional electron gas after plasma treatment recovered significantly at the temperature of 500 °C. By using C-V measurement, it was possible to assess besides the changes of the two-dimensional electron gas concentration after annealing also the changes in the Schottky barrier heights and to find out the doping concentration in AlGaN barrier and GaN channel layer. The trend in Schottky barrier height changes after annealing was confirmed also by I-V measurement.     

Interface properties of an O2 annealed Au/Ni/n-Al0.18Ga0.82N Schottky contact

We oxidized a Ni/Au metal bi-layer contact fabricated on HVPE Al_0.18Ga_0.82N from 373 K to 573 K in 100 K steps. In the range 1 kHz to 2 MHz, the Capacitance–Voltage–Frequency (C–V–f) measurements reveal a frequency dispersion of the capacitance and the presence of an anomalous peak at 0.4 V owing to the presence of interface states in the as deposited contact system. The dispersion was progressively removed by O₂ anneals from temperatures as low as 373 K. These changes are accompanied by an improvement in the overall quality of the Schottky system: the ideality factor, n, improves from 2.09 to 1.26; the Schottky barrier height (SBH), determined by the Norde [1] method, increases from 0.72 eV to 1.54 eV. From the Nicollian and Goetzberger model [2], we calculated the energy distribution of the density of interface states, N_SS. Around 1 eV above the Al_0.18Ga_0.82N valence band, N_SS, decreases from 2.3×10¹² eV⁻¹ cm⁻² for the un-annealed diodes to 1.3×10¹² eV⁻¹ cm⁻² after the 573 K anneal. Our results suggest the formation of an insulating NiO leading to a MIS structure for the oxidized Au/Ni/Al_0.18Ga_0.82N contact.     

Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500 °C in steps of 100 °C for 1 h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500 °C, they change to slightly polycrystalline. The optical constants such as the refractive index (n_r), the extinction coefficient (k), and the real (ε₁) and imaginary (ε₂) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I-V curve, a nonlinear I-V curve owing to the Schottky contact is also found, and the barrier heights (?_bn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.     

Illumination dependence of I-V and C-V characterization of Au/InSb/InP(1 0 0) Schottky structure

The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He-Ne laser of 1 mW power and 632.8 nm wavelength. The current-voltage I(V_G), the capacitance-voltage C(V_G) measurements were plotted and analysed. The saturation current I_s, the serial resistance R_s and the mean ideality factor n are, respectively, equal to 2.03 × 10⁻⁵ A, 85 Ω, 1.7 under dark and to 3.97 × 10⁻⁵ A, 67 Ω, 1.59 under illumination. The analysis of I(V_G) and C(V_G) characteristics allows us to determine the mean interfacial state density N_ss and the transmission coefficient θ_n equal, respectively, to 4.33 × 10¹² eV⁻¹ cm⁻², 4.08 × 10⁻³ under dark and 3.79 × 10¹² eV⁻¹ cm⁻² and 5.65 × 10⁻³ under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C⁻²(V_G) characteristic.     

Crystallization and surface morphology of Au/SiO2 thin films following furnace and flame annealing

A crystallization and surface evolution study of Au thin film on SiO₂ substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10⁻⁷ mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO₂ substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO₂ system decreases in the range of 350-400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO₂ surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing in the range of 300-310 °C and by flame annealing of a few seconds and up to 0.5 min.     

Effect of annealing on TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by simple chemical precipitation method and annealed at different temperatures. The as-prepared TiO₂ are amorphous, and they transform into anatase phase on annealing at 450 °C, and rutile phase on annealing at 900 °C. The X-ray diffraction results showed that TiO₂ nanoparticles with grain size in the range of 21–24 nm for anatase phase and 69–74 nm for rutile phase have been obtained. FESEM images show the formation of TiO₂ nanoparticles with small size in structure. The FTIR and Raman spectra exhibited peaks corresponding to the anatase and rutile structure phases of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increase of annealing temperature.     

Auger electron spectroscopy of Au/NiOx contacts on p-GaN annealed in N2 and O2 + N2 ambients

We have designed a promising contact scheme to p-GaN. Au/NiO_x layers with a low concentration of O in NiO_x are deposited on p-GaN by reactive dc magnetron sputtering and annealed in N₂ and in a mixture of O₂ + N₂ to produce low resistivity ohmic contacts. Annealing has been studied of NiO_x layers with various contents of oxygen upon the electrical properties of Au/NiO_x/p-GaN. It has been found that the Au/NiO_x/p-GaN structure with a low content of oxygen in NiO_x layer provides a low resistivity ohmic contact even after subsequent annealing in N₂ or O₂ + N₂ ambient at 500 °C for 2 min.Auger depth profiles and transmission electron microscopy (TEM) micrographs reveal that while annealing in O₂ + N₂ ambient results in reconstruction of the initial deposited Au/NiO_x/p-GaN contact structure into a Au/p-NiO/p-GaN structure, annealing in N₂ brings about reconstruction into Au/p-NiO/p-GaN and Ni/p-NiO/p-GaN structures. Hence, in both cases, after annealing in N₂ as well as in O₂ + N₂ ambient, the ohmic properties of the contacts are determined by creation of a thin oxide layer (p-NiO) on the metal/p-GaN interface. Higher contact resistivities in the samples annealed in O₂ + N₂ ambient are most likely caused by a smaller effective area of the contact due to creation of voids.