Thermal Annealing In Vacuum Research Articles

SERS enhancement, sensitivity and homogeneity studies on bi-metallic Ag-Cu films through tuning of broad band SPR towards red region

The objective of this work is to obtain a strong and a broad visible surface plasmon resonance (SPR) and also to tune the wavelength towards red region in thermally evaporated bimetal Ag-Cu film which will act as relatively sensitive surface enhanced Raman spectroscopy (SERS) substrate for the application in bio molecule detection. For the optimization, the morphological property including surface roughness, number-particle density, size distribution and inter-particle distances were altered through varying Cu content in Ag-Cu and temperature by vacuum thermal annealing. The effective dielectric constant of Ag-Cu films is studied from theoretical simulation using extended Maxwell garnet method demonstrating a strong plasmonic character as compared to pure Ag and Cu films. The elemental composition and the surface oxidation states of Ag-Cu film are probed through X-ray photoelectron spectroscopy (XPS). SERS study of RhG molecules exhibit higher enhancement factor for Ag0.75Cu0.25 film (annealed at 100 °C) as compared to pure Ag and Cu by the factor of 1.6 and 50 respectively and congruently the limit of detection was found to be 10−9 M. The higher SERS homogeneity with the least standard deviation of 18% on RhG molecules was studied through Raman mapping and bar plot. A broad and visible SPR band optimized towards red region on Ag0.75Cu0.25film may improve the sensitivity of bio-molecules detection.

Enhancements of photoluminescence intensity in high-quality floating-zone Si by thermal annealing in vacuum

Inactivation of non-radiative defects by hydrogen and their thermal stabilities in a high-quality floating-zone Si wafer depending on annealing conditions have been studied using in-situ photoluminescence (PL) and thermal desorption under an ultra-high vacuum. The PL intensity increased to ∼400% of its initial value after annealing at 450 °C and decreased to ∼6% of its initial value after annealing at 600 °C due to inactivation and activation of non-radiative defects, respectively. Based on the annealing temperature- and duration-dependence of the PL intensity, we propose two types of hydrogenated defects with different thermal stabilities.

Structural and optoelectronic properties of CdCl2 activated CdTe thin films modified by multiple thermal annealing

Traditional CdCl2 thermal treatment of CdTe/CdS heterostructure results in grain growth, sintering and incorporation of Cl into CdTe lattice, substantially improving performance of the cells. The process is complicated by high vapor pressure of CdCl2 and presence of oxygen. Considering volatility of CdCl2 and presence of residual oxidation products we provide systematic investigation results on the influence of subsequent multiple annealing in hydrogen (H2), vacuum and closed isothermal conditions on the properties of CdCl2 activated CdTe films (thickness 2μm) deposited by close spaced sublimation at low (250°C) and high (500°C) substrate temperature onto roughened glass. Structural and optoelectronic properties of thermal annealed films were compared. High resolution X-ray analysis demonstrates the shift of the main (111) peak in accordance with mobility of CdCl2 impurity between ambient and CdTe crystal in good correlation with optoelectronic properties. CdCl2 activated CdTe films have high resistivity and high dark to light resistance ratio. Subsequent hydrogen and vacuum thermal annealing increases the resistivity and photoconductivity of the films. The dark resistivity has been sharply decreased by about four orders of magnitude in result of isothermal annealing at 600°C. By controlling the thermal annealing conditions, substantial improvement of CdTe optoelectronic properties has been achieved.

Solution-Processed Nanoscale Carbon Nanotube Thin-Film Transistors Fabricated By Electromigration

Solution-processed carbon nanotube thin-film transistors (CNT-TFTs) have been of great scientific and technological attention due to the merits of fabrication processes and structual integration. Significant improvements in material design and process optimization have resulted in high performance CNT-TFTs which are comparable to or better than conventional ones. However, it is still difficult to realize sub-nano-scaled solution-processed CNT-TFTs suitable for integrated circuits and systems. In order to fabricate a sub-nm gap between source and drain electrodes in the channel region of the solution-processed CNT-TFTs, the DC breakjunction method by applying the electric field to trap Au nanoparticles and to form a short bridge was investigated through electromigration. A gradually ramping electric bias was imposed on the contact junctions, thereby breaking the bridge into a sub-nm gap in TFTs. The combination of surface treatment and vacuum thermal annealing increased the density of the nanotubes in the channel region and improved charge injection between the channel and the source electrode. In this presentation, we will demonstrate the process optimization to realize high-performance solution-processed CNT-TFTs with a channel length of ~20 nm and discuss the effect of surface treatment and vacuum thermal annealing on device performance.

Evaluation of the Mechanical Properties of Multi-nano Layered Copper-Nickel Thin Film by the Dynamic-Nano Indentation Method

The dynamic nano-indentation method was applied to study the effect of interface moving behavior with heat treatment on the nano-mechanical properties of multi-nano-layered copper-nickel thin film. Layer-by-layer depositions of copper and nickel of nano-sized thickness were prepared by two-step pulse electro-deposition in a modified copper-nickel sulfate bath at 25°C. The multi-layered copper-nickel thin sheet was composed of a 20-nm-thick copper-rich nickel phase, and a 25-nm-thick nickel-rich copper phase. Thermal vacuum annealing influenced the interface morphology between copper and nickel nano-layers. Inter-diffusion mainly occurred after annealing at 500°C for 6 h. The interface disappeared after annealing at 600°C to form a completely solid solution. Thermal annealing reduced the nano-hardness and elastic recovery. The average nano-hardness of the multi-layered nano-copper-nickel thin film for the specimens of as-received, 300°C, 500°C and 600°C were 7.9 Gpa, 6.1 Gpa, 4.7 Gpa and 3.0 GPa, respectively. The elastic stiffness was 15.77 × 104 Nm−1 for the as-received specimen, which finally became 2.98 × 104 Nm−1 for the specimen after annealing at 600°C for 6 h.

Influence of ion-plasma treatment on residual stress in the microcantilever

The influence of ion-plasma treatment on residual stress in the microcantilever is investigated. The ability of treatment with energy below the sputtering threshold to affect the mechanical stress is shown. It is also demonstrated that a preliminary vacuum thermal annealing of samples reduces the influence of ion bombardment on the residual stress. With the increase of the annealing temperature the effect of ion bombardment disappears.

Phosphorous doping in vertically aligned ZnO nanorods grown by wet-chemical method

The synthesis of well-aligned highly crystalline phosphorous (P) doped ZnO nanorods (ZnO:P) on glass substrates is demonstrated here. Vertically aligned ZnO nanorods are fabricated by a two-step method comprises of nanocrystalline ZnO seed layer formation by dc sputtering technique followed by solution growth of ZnO nanorods. To incorporate P, aligned ZnO nanorod films are exposed to P vapor in a vacuum chamber and then subjected to rapid thermal annealing in vacuum at an elevated temperature of 450 °C. Scanning electron microscopy and X-ray diffraction measurement confirm the growth of highly crystalline well aligned hexagonal ZnO nanorods that are perpendicular to the substrate surface. The optical band gap estimated from the transmittance spectra recorded by a UV–VIS–NIR spectrophotometer is 0.24 eV lower for ZnO:P compared to ZnO nanorods. Vibrational properties of ZnO:P nanorods are studied by FTIR and Raman spectra. Raman peak appeared at 355 cm−1 for ZnO:P is due to the Zn-site substituted by phosphorous. For ZnO nanorods, the room temperature photoluminescence (PL) spectra shows a sharp UV emission peak due to near band edge transition and a broad blue–green emission peak due to defect related transition. The observed red shift for the UV emission peak in the ZnO:P nanorods is associated with the shrinking band gap whereas the intense and broad blue–green emission peak is due to defects introduced with P doping.

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

Gd-doped ZnO thin films were prepared using pulsed laser deposition at different oxygen pressures and varied Gd concentrations. The effects of oxygen deficiency-related defects on the Gd incorporation, optical and structural properties, were explored by studying the impact of oxygen pressure during deposition and post-growth thermal annealing in vacuum. Rutherford Backscattering Spectrometry revealed that the Gd concentration increases with increasing oxygen pressure for samples grown with the same Gd-doped ZnO target. Unexpectedly, the c-lattice parameter of the samples tends to decrease with increasing Gd concentration, suggesting that Gd-defect complexes play an important role in the structural properties. Using low-temperature photoluminescence (PL), Raman measurements and density functional theory calculations, we identified oxygen vacancies as the dominant intrinsic point defects. PL spectra show a defect band related to oxygen vacancies for samples grown at oxygen deficiency.

High-Performance Single-Walled Carbon Nanotube-Based Thin-Film Transistors by Reducing Charge Transfer

We demonstrate high-performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) using the simple and robust method of an interacting fluoropolymer encapsulation with thermal annealing in vacuum to reduce the charge transfer. With an optimized combination of the fabrication process and the device configuration, drop-casted SWCNT-TFTs exhibit a field-effect mobility of $\sim 18$ cm2/ $\text{V}\,\cdot \, \text{s}$ in the linear regime, an ON–OFF-current ratio of $\sim 10^{6}$ , a threshold voltage of around 0 V, and a subthreshold swing of 97 mV/decade, which is among the best results that have been achieved in 2-D random networks of the SWCNTs. We also investigate the instability characteristics in the SWCNT-TFTs encapsulated with fluoropolymer during the prolonged electrical bias-stress. Interestingly, the drop in drain current of the SWCNT-TFTs was partially recovered with a second phenomenon that increases the drain current after a certain time. The hydrophobic surface that the fluoropolymer film possesses, reduced the chemical interaction of charge carriers with the hydroxyl (–OH) functional groups which act as defects in the SWCNT-TFTs.

Ring structures formed inside voids in SiO2 layer on Si(100) during thermal decomposition

Ring structures inside voids in the SiO2 layer on a Si(100) substrate, which are concentrically formed by repeating thermal annealing in vacuum, have been investigated by scanning electron microscopy and atomic force microscopy. We demonstrate that slight exposure of the surface to volatile organic compounds during a cooling process significantly affects the formation of the ring structures. This result clearly shows that the key to ring-structure formation is surface adsorption of carbon atoms, which probably suppresses surface migration of silicon atoms. Our research provides a novel technique for the fabrication of nanostructured semiconductors for such applications as quantum effect devices.

Raman spectroscopy study of graphene thin films synthesized from solid precursor

In this work, we present Raman spectroscopy study of graphene thin films obtained by rapid thermal annealing in vacuum. As a carbon source, we used spectroscopic graphite electrodes cut into small pieces on top of which we deposited copper/nickel thin films. Samples were then annealed at different annealing temperatures (600, 700, 800 and 900 °C) for 30 min. Raman spectroscopy study showed that annealing at lower annealing temperatures (600 and 700 °C) leads to formation of single layer graphene thin films with relatively high level of defects. Annealing at higher annealing temperatures (800 and 900 °C), on the other hand, resulted in formation of homogenous multilayer graphene thin films. From Raman spectra, we also concluded that samples annealed at higher annealing temperatures had lower level of defects compared to the samples annealed at lower annealing temperatures.

Healing of oxygen defects on VO2 surface: F4TCNQ adsorption

Oxygen-defect vacancies that routinely exist in wet production of VO2 material or on the surface of VO2 single crystal after surface treatment have significant influence on the metal-insulator phase transition features mainly due to their enhanced effect of doping on V 3d electronic structure. The removal of the surface oxygen defects is highly desired for investigating the VO2 intrinsic electronic properties. In this work, we propose a charge transfer doping method by using strong electric affinity molecule tetrafluorotetracyanoquinodimethane (F4TCNQ) adsorption rather than the normal thermal annealing in oxygen atmosphere to heal the surface oxygen defects of VO2 crystalline film. The healing effect is probed by the electronic structure evolution at the F4TCNQ/VO2 interface. The VO2 crystalline film is grown by an oxygen plasma assisted molecular beam epitaxy method on an Al2O3(0001) substrate. Surface oxygen defects on VO2 film are produced after a mild sputtering with an ionic energy of 1 keV and a thermal annealing in vacuum at 100 ℃. The influence of F4TCNQ molecule adsorption on the electronic structure of the sputtered VO2 film is studied by using in-situ synchrotron-based photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). XPS and XAS results demonstrate convincingly that V3+ species of sputtered VO2 are oxidized into the V4+ and simultaneously negative molecular ions form at F4TCNQ/VO2 interface resulting from the electron transfer from VO2 to the F4TCNQ layer. The preferred adsorption on surface defects and the strong electron withdrawing function of F4TCNQ molecules may account for the effective elimination of the electron doping effect of oxygen defects on VO2 surface. This charge transfer effect at interface recovers the electronic properties of VO2. Compared with thermal annealing in oxygen environment, the healing of oxygen defects by the molecular adsorption can prevent the surface from over oxidating VO2 into V2O5, which opens a new route to surface defect healing.

Carbon as Quasi-Reference Electrode in Unconventional Lithium-Salt Containing Electrolytes for Hybrid Battery/Supercapacitor Devices

Metallic lithium is the most widespread reference electrode in lithium ion battery research, but its high reactivity limits the usage primarily to conventional carbonate based electrolytes. Novel high power concepts, like hybrid supercapacitors, require lithium containing electrolytes with high ionic conductivity (e.g., acetonitrile), which are not always stable versus lithium. In the current work we face this issue by refining activated carbon as a quasi-reference electrode originally employed for conventional supercapacitors. Different commercially available carbon powders were examined as reference electrode materials and calibrated in lithium-salt containing acetonitrile versus Li+ intercalation/de-intercalation reaction of nanoparticulate Li4Ti5O12. The stability of the activated carbon reference electrode is highly affected by the salt employed and decreases in the following order: LiTFSI > LiClO4 > LiPF6 > LiBF4. Only a negligible impact of electrolyte solvent, pore size distribution and reference electrode binder was observed. Furthermore, activated carbon was functionalized (HNO3 treated) and de-functionalized (thermal annealing in vacuum or hydrogen) to investigate the impact of carbon functionalization on the reference electrode stability. Nitrogen and oxygen containing surface groups have been found to drastically improve long-term stability of activated carbon quasi-reference electrodes. Even after 15 days exposed to the electrolyte, the potential of HNO3 treated activated carbon is marginally altered by 10 mV.

磁控溅射工艺引起硅表面超薄钝化层电子结构变化

During fabrication of TCO/SiO x /n-Si (SIS) photovoltaic devices, deposition of TCO films by sputtering damages the electronic structure of the SiO x /c-Si interface, leading to higher interface recombination rate and lower open circuit voltage of the obtained photovoltaic device. Enhancing the interface recombination rate is equivalent to decreasing the diffusion length in the bulk and reducing the short circuit current. It is obvious that damage to the interface can seriously affect the overall performance of the device. Usually, researchers are only concerned with the effect of passivation before TCO film deposition by sputtering, or with the overall performance of the fabricated device; thus, the damage incurred by sputtering during device fabrication is often overlooked. The damage incurred by sputtering on the efficient silicon-based heterojunction solar cells, especially the SIS devices, is rarely considered. In this letter, we report the investigations of the damage incurred by the energetic particle beams in the plasma (atoms/ions and UV glow) on the atomic bonding and electronic states in both ultra-thin silicon oxides and SiO x (1.5-2.0 nm)/c-Si(150 μm) samples interface. The analysis was performed by using vacuum thermal annealing, effective minority carrier lifetime measurements (by using μ-PCD), and surface X-ray photoemission spectroscopy (XPS). The damage was observed in the process of magnetron sputtering deposition of the ITO thin film. We also investigated the effective passivation function of the ITO thin films silicon surface. The results show that the samples lifetime was reduced by more than 90% (from 105 μs to 5 μs) after the sputtering deposition of the ITO thin film. However, vacuum annealing at 100-400°C for 30 min partially eliminated the damage to the SiO x /c-Si interface and improved the passivation effect of the thin oxide layer on the crystalline silicon. Vacuum annealing at 200°C for 30 min restored the lifetime to nearly 30 μs; this annealing temperature corresponds to the typical temperature for the preparation processes of most efficient crystalline silicon heterojunction photovoltaic devices. However, vacuum annealing at 500-700°C for 30 min yielded a lifetime of about 3 μs. The analysis performed by comparing the results of XPS depth profiling revealed that the gaseous unstable material SiO is generated at the SiO x /c-Si interface under this annealing condition, which damages the SiO x /c-Si interface and augments the unsaturated bond silicon oxide SiO x (0 x <2), increasing the density of interface states, resulting in the lifetime attenuation. Therefore, low-temperature vacuum annealing can partially reduce the sputtering-induced structural damage, which prompts studying the effects of magnetron sputtering damage, and is also helpful for constructing the SIS photovoltaic devices and improving their performance.

Towards reversible control of domain wall conduction in Pb(Zr0.2Ti0.8)O3 thin films

Control over the localised conductance recently observed at ferroelectric domain walls is key for their integration into potential nanoelectronics devices. Using a combination of piezoresponse force microscopy and local conductance mapping, we demonstrate switching between conducting and insulating behavior at 180° domain walls in epitaxial Pb(Zr0.2Ti0.8)O3 thin films subjected to ultrahigh vacuum thermal annealing or exposed to ambient conditions, respectively. The reversibility of this behavior is demonstrated in repeated annealing-exposure cycles. To explain these observations, we propose a mechanism based on changes in electrostatic and chemical boundary conditions through oxygen vacancy redistribution and the removal of surface adsorbates.

Irradiation-induced TiO2 nanorods for photoelectrochemical hydrogen production

In this work, well-ordered nanorods were fabricated on the surface of TiO2 thin films deposited on Ti sheets by an ion irradiation method using nitrogen ion irradiation with the energy of 65 keV to a fluence of 1 × 1017 ions/cm2. These TiO2 nanorods are about 120 nm in length and 20–40 nm in diameter. After post-irradiation annealing at 500 °C in O2, the nanorod array photoelectrode displays largely enhanced performance for photoelectrochemical (PEC) water splitting compared to that of the un-irradiated TiO2 thin films with a planar structure. The influences of the irradiated ion energy on the morphology and photocurrent density of the nanorods were investigated. The 65 keV N+ irradiated TiO2 thin films shows a higher photocurrent density than those of the 45 and 85 keV N+ irradiated TiO2 thin films. We also discussed the influence of annealing conditions on the PEC performance of TiO2 nanorods, and it was found that the nanorods annealed at 600 °C in vacuum produce a much higher photocurrent density of 0.6 mA/cm2 at 0.8 V (vs. a saturated calomel electrode), which is about 7 times higher than that of the nanorods annealed in oxygen. This work proposes that ion irradiation combination with thermal annealing in vacuum could be an effective approach for developing nanostructured materials for water splitting.

Thermal annealing: a facile way of conferring responsivity to inert alkyl-chain-passivated nanoparticle arrays.

This work demonstrates a facile post-treatment strategy, vacuum thermal annealing, to fabricate a dodecanethiol-passivated gold nanoparticle (Au NP) array with organic solvent sensitivity. Through investigating the structure change of the Au NP array, it was found that the interparticle distance decreased during vacuum heat treatment, which meant a closer arrangement of the particles and a more dense packing of the dodecanethiol ligands in the interparticle region. The condensation would increase the interaction of the alkyl chain and enhance their interdigitation. Furthermore, on the basis of the stretching of the alkyl chains in organic solvents, the thermally treated Au NP array showed a good response to organic solvent or vapor by using the interdigitated dodecanethiol network as its responsive unit. The alkyl chains stretch to different extents in different organic solvents, leading to differences in interparticle distance, which provided a distinct blue shift of maximum wavelength upon exposure to various organic solvents or vapors. All of these results indicated that thermal annealing was an efficient way to confer responsivity to inert Au NP arrays. Together with the cost-effectiveness of such NP arrays, this study has potential in the development of economical sensors for medical diagnostics, food safety screening, and environmental pollution monitoring.

Effective and tunable light trapping in bulk heterojunction organic solar cells by employing Au-Ag alloy nanoparticles

Effective and tunable light trapping in organic solar cells (OSCs) has been demonstrated by employing Au-Ag alloy nanoparticles (NPs). A simple vacuum thermal annealing method has been employed to fabricate the Au-Ag alloy NPs with tunable molar ratio, and thereafter tunable localized surface plasmon resonance (LSPR). The incorporation of the alloy NPs with an appropriate molar ratio into the OSCs structures supports amplification of the electric field near the particles surface through LSPR and results in an enhanced light absorption at the absorption wavelength region of the absorber owing to the near field coupling. The short-circuit photocurrent density of the alloy NPs-based OSCs is improved from 7.37 to 8.74 mA/cm2 compared to that of control OSCs, and the efficiency of 3.03% is obtained, which corresponds to an enhancement factor of 19%.

Enhanced visible light photocatalysis of cuprous oxide nanoparticle modified zinc oxide nanowires

We report on the excellent photocatalytic activity of Cu2O nanoparticle (NP) modified ZnO nanowires (NWs) in the visible light range. The NP modification is realized by photoreduction and subsequent thermal annealing in vacuum. Transmission electron microscopy analysis confirms that the NPs are in the form of Cu2O. For the degradation of a 50μM rhodamine B solution under the illumination of a halogen lamp, the zeroth-order kinetic constant of the NP modified NWs is around 0.22μMmin−1 and 8.8 times as high as that of as-grown NWs. The achieved performance compares well with reported results of visible light photocatalysis of NP modified ZnO NWs. Furthermore, a kinetic constant of 0.53μMmin−1 and a degradation efficiency of 97% in 2h have been obtained by using sunlight illumination.

Silicon Nitride Thickness Dependent Electrical Properties of InAlN/GaN Heterostructures

Introduction Lattice-matched InAlN/GaN/Si based high electron mobility transistors (HEMTs) have recently attracted much attention as a candidate for next generation high-power, high-temperature and high-frequency devices, due to their higher charge density than the conventional AlGaN/GaN heterostructure [1]. However, HEMT performance, reliability, integrity and robustness are determined by the contact materials employed and passivation. Various dielectrics, such as SiO2, Si3N4, AlN, MgO, Al2O3, HfO2, Sc2O3, etc have been investigated for passivation. Among them, Si3N4 is the most widely used. Extensive improvement in electrical properties of the AlGaN/GaN/Si heterostructure achieved by the SiN x passivation process has been reported [2]. Such improvements by SiN x passivation were believed to be due to the reduction of the surface states, change in the AlGaN potential barrier height or increase of the 2DEG density at the channel due to tensile stress [3-5]. In spite of various reports on SiN x pasivation of InAlN/GaN heterostructures, SiN x thickness dependent studies have not been extensively explored to date. In the present study, we report SiN x thickness dependent electrical properties and its effect on the device performance of InAlN/GaN heterostructures. Experiment Nearly lattice-matched InAlN/GaN/Si epi-wafer, with a sheet resistance of 348.9 Ω/sq, was used in the present study. Prior to ohmic contact formation, InAlN/GaN/Si substrate surface was ultrasonically cleaned with acetone, IPA and DI water. Hf (15)/Al (200)/Ta (20) nm ohmic contacts were deposited by sputtering followed by rapid thermal annealing in vacuum at 600 oC for 1 min. No surface treatment was performed prior to passivation. Passivation SiN x layer of varying thickness ranging from 25 to 200 nm was deposited at 300°C by PECVD using silane and ammonia as precursor gases. SiN x layer on the ohmic electrodes was removed by etching in buffered hydrofluoric acid. To characterize our samples, room-temperature Hall measurements using van der Pauw geometry and ultraviolet (UV) Photoluminescence (PL) spectra excited using 266 nm laser source were performed. Results and Discussion Figure 1 shows the room-temperature Hall measurements of InAlN/GaN/Si as a function of the passivation SiN x layer thickness. Increase in sheet carrier concentration (ns), whereas decrease in mobility (μ) is observed with increasing SiN x passivation layer thickness. A thickness of ~100 nm can be viewed as optimum as it yields a minimum sheet resistance (Rs), as shown in Fig. 1. The corresponding increase in ns is substantial of almost ~30%, with respect to sample without SiN x passivation. Although the reason for the significant increase in ns is not apparent, yet our preliminary studies by means of UV PL reveal a shift in the PL peak position of the GaN channel layer (Fig. 2), which is most likely due to band bending under stress. However, possibility of reduction of surface states of the passivated InAlN and/or an increase in positive charge at the SiN x /InAlN interface cannot be ruled out. Additionally, the decrease in μ is possibly due to increased electron-electron scattering and/or interface roughness scattering with such a high carrier concentration in 2DEG channel. Interestingly, the trend of increase in 2DEG density is similar to that observed for AlGaN/GaN heterostructure under different SiN x passivation layer thickness [6]. This observation indicates that the intrinsic property of SiN x film may be playing a critical role in the enhancement of 2DEG density rather than the interface property. Further studies to establish the mechanisms responsible for the enhancement in 2DEG density as well as to evaluate the influence of passivation layer thickness on the device performance are in progress. Conclusion In conclusion, surface passivation of InAlN/GaN heterostructures with PECVD SiN x of varying thickness has been investigated. A thickness of ~ 100 nm is found to be optimum and has yielded a minimum sheet resistance. The corresponding 2DEG density change is substantially higher (by ~30 %) than sample without SiN x passivation, and this enhancement is attributed possibly to band bending under stress.