Effects of thermal annealing on the electrical and structural properties of Pt/Mo Schottky contacts on n-type GaN

Thermal annealing temperature effects on the electrical and structural properties of platinum/molybdenum (Pt/Mo) Schottky contacts on n-type GaN have been investigated by current–voltage (I–V), capacitance–voltage (C–V), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. As-deposited Pt/Mo/n-GaN Schottky diode exhibits barrier height of 0.75 eV (I–V) and 0.82 eV (C–V). Upon annealing at 400 and 500 °C, the barrier height slightly increased to 0.77 eV (I–V) and 0.92 eV (C–V) and 0.82 eV (I–V) and 0.97 eV (C–V), respectively. A maximum barrier height of 0.83 eV (I–V) and 0.99 eV (C–V) is obtained on the Pt/Mo contacts annealed at 600 °C. X-ray photoelectron spectroscopy results shows that the Ga 2p core-level shift towards the low-energy side for the contact annealed at 600 °C as compared to the as-deposited one. Based on the results of XPS and XRD studies, the formation of gallide phases at Pt/Mo/n-GaN interface could be the reason for the increase of Schottky barrier heights upon annealing at elevated temperatures. The atomic force microscopy (AFM) results showed that the Pt/Mo contact does not seriously suffer from thermal degradation during annealing even at 600 °C (RMS roughness of 5.41 nm). These results make Pt/Mo Schottky contacts attractive for high temperature device applications.     

Microstructural and electrical characteristics of rapidly annealed Ni/Mo Schottky rectifiers on cleaned n-type GaN (0001) surface

We have investigated the electrical and microstructural properties of Ni/Mo Schottky rectifiers to n-type GaN by current–voltage (I–V) and transmission electron microscopy (TEM) before and after annealing at 600 °C. The obtained barrier height for as-deposited Ni/Mo contact is 0.66 eV. It is observed that the barrier height increases with annealing temperature up to 500 °C, reaching a maximum value of 0.75 eV at this temperature. However, the Schottky barrier height of the Ni/Mo Schottky contact slightly decreased to 0.67 eV (I–V) when the contact was annealed at 600 °C. According to the HRTEM, STEM and EDX analysis, the formation of Ga-Ni interfacial layer at the interface results in the accumulation of gallium vacancies near the surface of the GaN layer. This could be the reason for increase in barrier heights upon annealing at elevated temperatures. The variation in the measured barrier height after annealing at 600 °C may be due to the formation of native oxide layer at the interface compared to the 500 °C annealed contact.     

Thermal annealing behaviour on Schottky barrier parameters and structural properties of Au contacts to n-type GaN

We have investigated the thermal annealing effects on electrical and structural properties of Au Schottky contacts on n-type GaN using current–voltage (I–V), capacitance–voltage (C–V), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements. The calculated Schottky barrier height of the as-deposited Au/n-GaN diode was 0.85 eV (I–V) and 1.4 eV (C–V), respectively. However, after annealing at 300 °C it was found that the Schottky barrier height (SBH) slightly decreased to 0.77 eV (I–V) and 1.24 eV (C–V), and then slightly increased to 0.83 eV (I–V) and 1.30 eV (C–V) when the contact was annealed at 400 °C. With further increase in annealing temperature to 500 °C the barrier height was decreased and the respective values are 0.73 eV (I–V) and 1.02 eV (C–V). Based on the X-ray diffraction and RBS results, the formation of gallide phases at the Au/n-GaN interface could be the reason for variation in the Schottky barrier heights upon annealing temperatures.     

Electrical, structural and morphological characteristics of rapidly annealed Pd/n-InP (100) Schottky structure

The electrical and structural properties of the Pd/InP (100) Schottky barrier diodes have been investigated as a function of annealing temperature by current–voltage (I–V), capacitance–voltage (C–V) and X-ray diffraction (XRD) measurements. The Schottky barrier height of the as-deposited, 100 and 200°C annealed contacts determined from the I–V and C–V measurements are 0.56 and 0.81 eV, 0.57 and 0.81 eV, and 0.58 and 0.82 eV, respectively. However, both the measurements showed that the Schottky barrier height of the Pd/n-InP Schottky contact is increased to 0.59 eV (I–V) and 0.83 eV (C–V) when the contact is annealed at 300°C for 1 min in nitrogen atmosphere. Further Schottky barrier height decreases to 0.57 eV (I–V), 0.71 eV (C–V) and 0.53 eV (I–V), 0.67 eV (C–V) after annealing at 400 and 500°C samples. The result shows that the optimum annealing temperature for the Pd/InP Schottky diode is 300°C. Norde method is also used to determine the barrier height of Pd Schottky contacts and the values are 0.56 eV for the as-deposited contact, 0.57, 0.57, 0.58, 0.57 and 0.54 eV for contacts annealed at 100, 200, 300, 400 and 500°C which are consistent with the values obtained by the I–V measurements. From the atomic force microscopy results, it is evident that the overall surface morphology of the Pd/InP Schottky diode is fairly smooth. Based on the XRD results, the formation of phosphorus-oxygen compounds at the interface may be responsible for the variation in barrier heights observed in Pd/InP Schottky contacts with annealing temperature.     

Effect of annealing temperature on electrical characteristics of ruthenium-based Schottky contacts on n-type GaN

The electrical properties of ruthenium (Ru) and ruthenium/gold (Ru/Au) Schottky contacts on n-type GaN are investigated as a function of annealing temperature by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Schottky barrier height of as-deposited Ru/n-GaN is found to be 0.88 eV (I–V) and 1.10 eV (C–V) respectively. However, after annealing at 500°C for 1 min in the nitrogen ambient, the decrease in barrier height is quite considerable and found to be 0.80 eV (I–V) and 0.86 eV (C–V). In the case of Ru/Au Schottky diode the measured barrier height is 0.75 eV (I–V) and 0.93 eV (C–V). In contrast to the Ru contacts, it is interesting to note that the barrier height of Ru/Au depends on the annealing temperature. Annealing at 300°C improves the barrier height and the corresponding values are 0.99 and 1.34 eV. Further increase in annealing temperature decreases the barrier height and the respective values are 0.72 and 1.08 eV at 500°C. From the above observations, it is clear that the electrical properties of annealed Ru/Au contacts are improved compared to the as-deposited films. However, Ru Schottky contacts exhibit a kind of thermal stability during annealing.     

Electrical and structural properties of double metal structure Ni/V Schottky contacts on n-InP after rapid thermal process

The electrical, structural, and surface morphological properties of Ni/V Schottky contacts have been investigated as a function of annealing. The Schottky barrier height value from I–V and C–V measurements for as-deposited Ni/V/n-InP diode is 0.61 eV (I–V) and 0.91 eV (C–V), respectively. It has been observed that the Schottky barrier height decreases with increasing annealing temperature as compared to the as-deposited contact. For the contact annealed at 200 °C, the obtained barrier height decreased to 0.52 eV (I–V) and 0.78 eV (C–V). Further, the annealing temperature increased to 300 and 400 °C, the barrier height slightly increased to 0.58 eV (I–V), 0.82 eV (C–V) and 0.59 eV (I–V), 0.88 eV (C–V). However, after annealing at 500 °C, results then decrease in barrier height to 0.51 eV (I–V) and 0.76 eV (C–V), which is lower than the value obtained for the sample annealed at 200 °C. The Norde method is also employed to extract the barrier height of Ni/V/InP Schottky diode, and the values are 0.68 eV for the as-deposited and 0.56 eV for the contact annealed at 500 °C, which are in good agreement with those obtained by I–V technique. Based on the results of AES and XRD studies, it is concluded that the formation of indium phases at the Ni/V/n-InP interface may be the reason for the increase in the barrier height for the as-deposited contact. The decrease in the barrier height upon annealing at 500 °C may be due to the formation of phosphide phases at the interface. The AFM results showed that there is no significant degradation in the surface morphology (RMS roughness of 0.61 nm) of the contact even after annealing at 500 °C.     

Schottky barrier characteristics of Pt contacts to all sputtering-made n-type GaN and MOS diodes

All sputtering-made Pt/n-GaN [metal–semiconductor (MS)] and Pt/SiO₂/n-GaN [metal–oxide–semiconductor (MOS)] diodes were investigated before and after annealing at 500 °C. n-GaN, Pt, and SiO₂ films were all fabricated by the cost-effective radio-frequency sputtering technique. A cermet target was used for depositing GaN. The Schottky barrier heights (SBHs) of both MS and MOS Schottky diodes have been investigated by the current–voltage (I–V) measurements. The results showed that SBHs increased after annealing at 500 °C for 20 min in N₂ ambient, compared to the as-deposited at 400 °C. By using Cheung’s and Norde methods, the highest SBHs of MOS Schottky diodes were respectively found to be 0.79 and 0.91 eV for the as-deposited and had reached to 0.81 and 0.94 eV after annealing. The annealed Schottky diode had showed the higher SBH, lower leakage current, smaller ideality factor, and denser microstructure.     

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.     

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.     

Electrical characteristics and stability of gold and palladium Schottky contacts on ZnO nanorods

The electrical characteristics and stability of Pd and Au Schottky contacts on ZnO nanorods grown on glass substrate have been investigated. The nanorods were grown using the aqueous chemical growth method. The nanorods were characterized with scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). Prior to the metal contact deposition, an insulating PMMA layer was deposited between the nanorods. The best-produced Schottky contact was an as-deposited Pd/ZnO contact with an ideality factor of 1.74 ± 0.43 and a barrier height of 0.67 ± 0.09?eV. The relatively high ideality factor indicates that the current transport cannot be described by pure thermionic transport. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Post metal deposition annealing at 150?°C for 30?min in air lowered the barrier height and decreased the Au/ZnO ideality factor but increased it for Pd/ZnO. The current follows ohmic behavior when the applied forward bias, V(forward), is lower than 0.1?V, whereas for V(forward) between 0.1 and 0.45?V the current follows I～exp(cV), and at higher forward biases the current-voltage characteristics follow the relation I～V(2), indicating that the space-charge current-limiting mechanism is dominating the current transport.     

The influence of rapid thermal annealing on electrical and structural properties of Pt/Au Schottky contacts to n-type InP

The electrical and structural properties of Pt/Au Schottky contacts to n-InP have been investigated in the annealing temperature range of 200–500 °C by current–voltage (I–V), capacitance–voltage (C–V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The barrier height of as-deposited Pt/Au Schottky contact is found to be 0.46 eV (I–V) and 0.68 eV (C–V). For the contacts annealed at 300 °C, the barrier height is increased to 0.51 eV (I–V) 0.89 eV (C–V). Further increase in annealing temperature up to 500 °C, the barrier height has been found to decrease to 0.49 eV (I–V) 0.82 eV (C–V) from those values obtained at 300 °C. It has been found that the electrical characteristics are significantly improved for Pt/Au Schottky contacts upon annealing at 300 °C. Based on the Auger electron spectroscopy and X-ray diffraction results, the formation of Pt–In and Au–In intermetallic compounds at the interface may be the reason for the increase of barrier height after annealing at 300 °C for Pt/Au Schottky contacts. From the atomic force microscopy (AFM) results, it is evident that the surface becomes smooth with RMS roughness of 16.91 nm for the Pt/Au Schottky contacts after annealing at 500 °C compared to the 300 °C annealed sample (RMS roughness of 17.33 nm).     

Organometallic hybrid perovskites: structural,optical characteristic and application in Schottky diode

CH₃NH₃PbI₃ thin film was deposited by a dual-source evaporation system under high vacuum (~10^?4 Pa). The crystallographic phase of the thin film was determined by X-ray diffraction and its perovskite structure was confirmed. The crystal of annealed perovskite film was extremely smooth and significantly larger than that of as-deposited. The optical property of the thin film was investigated in the spectral range 300–1800 nm. By analyzing the absorption coefficient (α), the optical band gap (1.58 eV) and Urbach energy (0.082 eV) were revealed. The Al/CH₃NH₃PbI₃/ITO Schottky diode was fabricated in order to explore the potential applications of CH₃NH₃PbI₃. The basic device parameters, barrier height and ideality factor were determined by the current–voltage (I–V) measurement. It can be found that the charge transport was governed by space-charge-limited current mechanism by studying the forward bias characteristic.     

Schottky contacts of refractory metal nitrides on gallium nitride using reactive sputtering

Schottky contacts of refractory metal nitrides formed by reactive sputtering on n-type gallium nitride (GaN) were electrically evaluated, including film resistivity, Schottky characteristics and thermal stability. For the metal nitrides of TiN_x, MoN_x and ZrN_x, resistivities of 108.3, 159.0 and 270.0 μΩcm were obtained, respectively. Current-voltage (I-V) characteristics showed that the ideality factor varied from 1.03 to 1.16, while the Schottky barrier height (SBH) varied from 0.66 to 0.79 eV for the three kinds of Schottky contacts. Especially for the ZrN_x contact, the ideality factor and SBH were improved after annealing at 800 °C for 30 s. Schottky contact utilizing a refractory metal nitride on GaN shows its potential to develop thermally stable GaN devices.     

Analysis of current conduction mechanism in CZTSSe/n-Si structure

In this study, Cu₂ZnSn(S,Se)₄ (CZTSSe) thin films were deposited by the single step thermal evaporation process using the sintered powder of CZTSSe on soda lime glass (SLG) and Si wafer substrates. The structural, optical, and electrical properties of deposited films were investigated. Current–voltage (I–V) in the temperature range of 250–350 K, capacitance–voltage(C–V) and conductance–voltage (G/w–V) measurements at room temperature were carried out to determine electrical properties of CZTSSe/n-Si structure. The forward bias I–V analysis based on thermionic emission (TE) showed barrier height inhomogeneity at the interface and thus, the conduction mechanism was modeled under the assumption of Gaussian distribution of barrier height. The mean barrier height \(({\bar {\Phi }_{B0}})\) and standard deviation \(({\sigma _0})\) at zero bias were obtained as 1.27 eV and 0.18 V, respectively. Moreover, Richardson constant was obtained as 120.46 A cm^?2 K^?2 via modified Richardson plot and the density of interface states (D_it) profile was determined using the data obtained from forward bias I–V measurements. In addition, by the results of frequency dependent C–V measurements, characteristics of the interface state density were calculated applying high-low frequency capacitance (C_HF ? C_LF) and Hill–Coleman methods.     

Ti/Al/Ni/Au在N-polar GaN上的欧姆接触

N-polar GaN以其特有的材料特性和化学活性日益受到研究者关注,而N-polar GaN上欧姆接触也成为研究的热点。以Ti/Al/Ni/Au作为欧姆接触金属,分析了N-polar GaN上欧姆接触的最优退火条件,并借助剖面透射电子显微镜(TEM)和能量色散X射线能谱仪(EDX)研究了金属和N-polar GaN之间的反应生成物。结果表明,当退火温度升高到860℃时,可得到比接触电阻率ρc为1.7×10~(-5)Ω·cm~2的最优欧姆接触特性。TEM和EDX测试发现,除了生成已报道的AlN,还会在界面处产生多晶AlO_x,两者共同作用会进一步拉高势垒,从而对N-polar GaN上欧姆接触产生不利影响。     

Schottky diodes based on nanocrystalline p-GaN and n-GaN in thin film form

Nanocrystalline n-GaN and p-GaN in thin film form were deposited onto fused silica substrates by high-pressure d.c. magnetron sputtering of Si (1 at%) and Be (1 at%) doped GaN targets, respectively. Schottky diode structures for both the p- and n-type nanocrystalline GaN (Au/p-GaN/Al and Al/n-GaN/Au) were fabricated out of the above films. Corresponding current-voltage and capacitance-voltage characteristics of the Schottky diodes were recorded and analyzed in the light of the existing theories.     

Thermally stable and low-resistance W/Ti/Au contacts to n-type GaN

We report on the formation of thermally stable and low-resistance Ti/Au-based ohmic contacts to n-type GaN (4.0 × 10¹⁸ cm⁻³) by using a W barrier layer. It is shown that the electrical characteristic of the sample is considerably improved upon annealing at 900 °C for 1 min in a N₂ ambient. The contacts produce the specific contact resistance as low as 6.7 × 10⁻⁶ Ω cm² after annealing. The Norde and current–voltage methods are used to determine the effective Schottky barrier heights (SBHs). It is shown that annealing results in a reduction in the SBHs as compared to that of the as-deposited sample. Auger electron spectroscopy (AES), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) examinations show that nitride and gallide phases are formed at the contact/GaN interface. Based on the AES, STEM and XRD results, a possible ohmic formation mechanism is described and discussed.     

Pd/GaN(0001) interface properties

This report concerns the properties of an interface formed between Pd films deposited onto the surface of (0001)-oriented n-type GaN at room temperature (RT) under ultrahigh vacuum. The surface of clean substrate and the stages of Pd-film growth were characterized in situ by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), ultraviolet photoelectron spectroscopy (UPS), and low energy electron diffraction (LEED). As-deposited Pd films are grainy, cover the substrate surface uniformly and reproduce its topography. Electron affinity of the clean n-GaN surface amounts to 3.1 eV. The work function of the Pd-film is equal to 5.3 eV. No chemical interaction has been found at the Pd/GaN interface formed at RT. The Schottky barrier height of the Pd/GaN contact is equal to 1.60 eV.     

Al and Ti/Al contacts on n-GaN

Al(60 nm) and Ti(40 nm)/Al(160 nm) metal layers have been deposited by thermal evaporation onto n-GaN epitaxial layers grown by metal organic chemical vapour deposition (MOCVD) on a c-plane sapphire substrate. The samples have been annealed at 300, 400, 700 or 900 °C for 10 min in vacuum. The microstructural and electrical properties of the contacts have been investigated by electron microscopy, X-ray diffraction and by current-voltage measurements. As-deposited Al and Ti/Al contacts were rectifying with Schottky barrier heights below 0.35 eV and 0.38 eV, respectively. After heat treatment at 300 °C and 400 °C both contacts exhibited linear current-voltage characteristics. After annealing at 700 °C Al contacts became rectifying with a barrier height of 0.42 eV, while Ti/Al contacts remained nearly linear at the same temperature. The electrical characteristics and XRD analysis indicated that the upper metal in Ti/Al contact diffused in the Ti layer already during deposition. Cross-sectional transmission electron microscopy revealed that in the case of Ti/Al contacts, the continuity of the Ti layers ceased when annealing above 700 °C. X-ray diffractions showed, that a Ti₂N interface phase formed in Ti/Al contacts at 700 and 900 °C, and an AlN interface phase developed in the same contact at 900 °C.