Frequency Dependence Of Capacitance Research Articles

Wearable temperature sensors based on lanthanum-doped aluminum-oxide dielectrics operating at low-voltage and high-frequency for healthcare monitoring systems

The incorporation of lanthanum (La) into sol-gel based aluminum-oxide (Al2O3) dielectrics is investigated by analyzing the dielectric properties obtained from electrical capacitive measurements of metal-insulator-metal. The optimized La doping results in significantly suppressed variation of frequency-dependent capacitance of sol-gel based La-doped Al2O3 (LaAlO3) dielectrics even at high frequencies of ~ MHz. In addition, flexible temperature sensors with sol-gel based LaAlO3 dielectrics on polyimide substrates are demonstrated through investigations on the capacitive responses to different temperatures ranging from 30 to 200 °C at various frequencies from 100 Hz to 1 MHz. Without any buffer or passivation film, the proposed flexible temperature sensors achieved a high mechanical stability against cyclic bending tests with curvature radii from 10 to 5 mm. Finally, the feasibility of a healthcare monitoring system is demonstrated by utilizing wearable body-temperature sensor arrays consisting of sol-gel based LaAlO3 dielectrics. High-performance temperature sensor system is capable of analyzing interfacial temperature characteristics on human body between 30 and 40 °C in real-time and displaying them on the use's smartphone. We believe that this study is expected to significantly contribute to the field of wearable bioelectronics consisting of solution-processed metal-oxide dielectrics for healthcare monitoring systems.

Triazole-coumarin centered star-shaped polymer: Structural characterizations and electrical properties of graphene composites

In present study, new three-arm initiator containing coumarin group and new 4-(3-(4-methoxyphenyl)acryloyl) phenyl acrylate (MPAC) was synthesized. Three-armed star-shaped polymer was obtained by polymerization using ATRP method from the chlorine ends of the initiator. The structure characterization was performed by FT-IR, 1H-NMR, 13C-NMR spectroscopy techniques. Thermal analyzes were performed by using thermogravimetry (TGA) and differential scanning calorimetry analysis (DSC) techniques in a nitrogen atmosphere. Thermal decomposition activation energy (Ea) of star polymer was determined by the Flynn-Wall-Ozawa and Kissinger methods. The average activation energy in the range of 0.02-0.3 conversion range was determined as 115.28 kJ/mol and 152.72 kJ/mol, respectively. Polymer composites were prepared by adding graphene particles in different ratios (0.5%, 1.0%, 2.0%, and 4.0% by weight) to the polymer matrix. The dielectric properties of star polymer and graphene composites were investigated in a range of 100 Hz-20 kHz frequency. Besides, the dielectric properties of the pure polymer were examined as a function of frequency at different temperatures (25 °C, 40 °C, 55 °C, 70 °C,). Furthermore, the polymer/4% graphene composite/p-Si thin-film heterojunction diode properties were investigated using current-voltage (I-V) analysis at room temperature in dark. The electrical parameters of heterojunction diode such as the rectification ratio (RR), barrier height (Φb) and ideality factor (n) were investigated. The frequency dependence of capacitance and the role of interface states were examined. The results showed that chalcone substituted three-arm star polymer/4% graphene composite has a diode and capacitor characteristic.

Defect studies on short-wave infrared photovoltaic devices based on HgTe nanocrystals/TiO2 heterojunction

Narrow bandgap (<0.5 eV) colloidal semiconductor nanocrystals (e.g. mercury chalcogenides) provide practical platforms for next generation short wave infrared, mid wave infrared and long wave infrared optoelectronic devices. Until now, most of the efforts in the field of infrared active nanocrystals have been taken on synthesizing nanocrystals, determining quantum states and building different geometries for optoelectronic devices. However, studies on interface trap states in the devices made from these narrow band gap nanocrystals are mostly unexplored. Herein, we investigate the defects or traps in these nanocrystals—embedded devices, which will be critical for improving their optoelectronic performance. In this article, we fabricate HgTe nanocrystals/TiO2 based photovoltaic devices and used capacitance-voltage (C–V) and deep level transient spectroscopy (DLTS) to investigate and obtain quantitative information on deep level trap states. Interestingly, frequency dependent C–V measurements show two peaks in the capacitance at lower frequency (<40 kHz), which is attributed to the presence of trap states. However, at high frequency the presence of a weak hump-like structure almost at the center of above two peaks validate the role of interface traps. DLTS studies show that traps at the interface of HgTe nanocrystals/TiO2 acts as recombination centers having activation energies of 0.27, 0.4 and 0.45 eV with corresponding trap densities of 1.4 , 1. and 1. and estimated capture cross-sections of 6.3 , 7.5 and 3.7 , respectively. In this work, DLTS has revealed the existence of interface trap states and the frequency dependent capacitance measurements corroborate the effect of charge storage on the heterostructures built from these nanocrystals that helps in the development of futuristic devices.

Multiply Charged Conjugated Polyelectrolytes as a Multifunctional Interlayer for Efficient and Scalable Perovskite Solar Cells.

A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2 ) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.

Frequency-Agile Low-Temperature Solution-Processed Alumina Dielectrics for Inorganic and Organic Electronics Enhanced by Fluoride Doping.

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlOx) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlOx film capacitance of 166 ± 11 nF/cm2 is stable over a 10-1-104 Hz frequency range, far more stable than that of neat AlOx films (capacitance = 336 ± 201 nF/cm2) which falls from 781 ± 85 nF/cm2 to 104 ± 4 nF/cm2 over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlOx dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV-vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

Synthesis and photodiode properties of chalcone substituted metallo-phthalocyanine

In this study, we aimed to investigate the photodiode properties of the chalcone substituted-phthalocyanine complex due to the important physical properties of the phthalocyanine and chalcone compounds. For this purpose, in the first step, a heterocyclic chalcone compound (HC) bearing a pyridine and hydroxyl group was obtained from the reaction of 4′-hydroxyacetophenone with pyridine-3-aldehyde. In the second step, the chalcone-substituted phthalonitrile compound (HCA) was obtained by interacted 4-nitroftalonitrile with the compound HC in the presence of K2CO3 in DMF in an argon atmosphere. The new chalcone substituted metallo-phthalocyanine (HCA-Co) was synthesized from the reaction of compound HCA with Co (II) acetate according to heating of solid phase method under an inert atmosphere. The structure of HC and HCA-Co were fully characterized by using 1H, and 13C-APT NMR, FT-IR, elemental analysis, UV–Vis spectroscopy. The HCP-Co thin-film planar heterojunction diode was prepared. The organic layer was deposited onto the p-Si substrate to obtain an Al/p-si/phthalocyanine(HCP-Co)/Al diode. The current (I)- voltage (V) characteristics of heterojunction diode was measured under dark and illuminated conditions (20–100 mW/cm2) at room temperature. The electrical characteristics of the device were measured. The ideal factor value was found to be 5.20 and according to this value, the diode exhibits non-ideal behavior. The frequency dependence of capacitance and the role of interface states were examined. The results showed that chalcone substituted metallo-phthalocyanine has a photodiode and photocapacitor characteristic. Therefore, chalcone-linked metallo-phthalocyanine can be applied in solar tracking systems.

Trap analysis of composite 2D–3D channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C multi-heterostructure at different temperatures**Project supported by the National Key Research and Development Program of China (Grant No. 2018YFB1802100), the Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2020JM-191 and 2018HJCG-20), the National Natural Science Foundation of China (Grant Nos. 61904135, 61704124, and 61534007), the China Postdoctoral Science Foundation (Grant Nos. 2018M640957

The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases (3DEGs) at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional (2D)–three-dimensional (3D) channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure (DH:Si/C). Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure (SH:C). There are fast, medium, and slow trap states in DH:Si/C, while only medium trap states exist in SH:C. The time constant/trap density for medium trap state in SH:C heterostructure are (11 μs–17.7 μs)/(1.1 × 1013 cm−2·eV−1–3.9× 1013 cm−2·eV−1) and (8.7 μs–14.1 μs)/(0.7× 1013 cm−2·eV−1–1.9× 1013 cm−2·eV−1) at 300 K and 500 K respectively. The time constant/trap density for fast, medium, and slow trap states in DH:Si/C heterostructure are (4.2 μs–7.7 μs)/(1.5× 1013 cm−2·eV−1–3.2× 1013 cm−2·eV−1), (6.8 μs–11.8 μs)/(0.8× 1013 cm−2 · eV−1–2.8× 1013 cm−2 · eV−1), (30.1 μs–151 μs)/(7.5× 1012 cm−2 · eV−1–7.8× 1012 cm−2 · eV−1) at 300 K and (3.5 μs–6.5 μs)/(0.9× 1013 cm−2 · eV−1–1.8× 1013 cm−2 · eV−1), (4.9 μs–9.4 μs)/(0.6× 1013 cm−2 · eV−1–1.7× 1013 cm−2 · eV−1), (20.6 μs–61.9 μs)/(3.2× 1012 cm−2 · eV−1–3.5× 1012 cm−2·eV−1) at 500 K, respectively. The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.

Bias-Dependent Admittance Spectroscopy of Thin-Film Solar Cells: Experiment and Simulation

In the present contribution, we have measured and simulated room temperature bias- and frequency-dependent capacitances of thin-film solar cell devices. The results of both the simulations and experimental measurements are represented as 2-D contour plots showing the derivative of the capacitance with respect to the frequency multiplied by the frequency. These plots are called “loss maps,” because responses in these contour plots correspond to responses of different nonidealities in the devices. Using a 1-D drift-diffusion solver (SCAPS), we have simulated the responses of different nonidealities of the solar cell devices, such as series resistance, bulk defects, interface defects, back contact barrier, and absorber–buffer barrier. We have shown that some nonidealities have a quite recognizable trace in the loss map. Other nonidealities on the other hand show responses that look quite similar in the bias voltage and frequency space, making exact conclusions on the nature and position of the defect responses in thin-film solar cells most of the times difficult. We have compared the simulated results with experimental measurements of one of our Cu(In,Ga)Se2 (CIGS) solar cell devices and came to the conclusion that there is likely a bulk defect or a spike-like barrier at the CIGS–CdS interface present in our particular device. The loss map can, in some cases, be useful in order to analyze admittance spectroscopy data in a graphical and relatively intuitive way.

Accurate Modeling of the Capacitance of Through-Silicon Via Considering Minority Carrier Effects

The 3-D integration of integrated circuits based on through-silicon via (TSV) is a promising technology to achieve high-performance, multifunctional, and heterogeneous microsystem. The voltage-dependent and frequency-dependent TSV capacitances have a predominant impact on system performance. Accordingly, accurate electrical modeling of TSV capacitance is critical for system design. This article proposes an accurate small-signal analysis method capable of modeling the low-frequency and high-frequency TSV capacitances. The contribution of both fixed carriers and mobile carriers are considered in the model. Moreover, the minority carrier effects are incorporated to model the high-frequency capacitance accurately. The proposed model shows a good correlation with measurement and device-level simulation. Analysis and experiment demonstrate neglecting the minority carrier effects lead to huge inaccuracy of TSV capacitance, which can be up to 30.1% in the strong inversion region. Therefore, it is important to consider the minority carrier effects in the modeling of high-frequency TSV capacitance. In addition, the proposed model consumes small computational cost benefit from efficient iterative procedures.

Vertical limits of resistive memory scaling: The detrimental influence of interface states

This work elucidates the role of interface states of a metal-oxide-silicon device, the basic structure of CMOS integrated resistive random access memory (ReRAM) devices. By fabricating Au/Al2O3/Si ReRAM devices on silicon substrates oriented along ⟨100⟩ and ⟨111⟩ directions and employing the frequency dependence of capacitance and parallel conductance, we explore the role of interface trap densities (Dit) in the breakdown mechanism of ReRAM devices. In order to quantify the interface states, we measured the parallel conductance of the ReRAM devices as a function of frequency, which gives an accurate picture of the spread of Dit along the bandgap of silicon. Analysis of interface state density before and after the breakdown process reveals that the Si ⟨111⟩ surface is more prone to generate defects than Si ⟨100⟩ surfaces, and its elucidation is done by analyzing the pre-breakdown current behavior of the devices. Finally, the influence of the interface states on the thickness scaling is shown, where the thinner devices are inclined to have an earlier breakdown (Set voltage) due to the strong coupling with interface states.

Negative capacitance phenomena in Au/SrTiO3/p-Si heterojunction structure

In this study, temperature- and frequency-dependent capacitance and conductance measurements of the Au/SrTiO3/p-Si heterojunction structure were examined. Strontium titanate (SrTiO3) thin films were deposited on cleaned p-type (100)-oriented silicon substrates using radio frequency (RF) magnetron sputtering method at a substrate temperature of 500 °C. The temperature-dependent reverse and forward bias C–V and G/ω$$-V$$ characteristics of the Au/SrTiO3/p-Si heterojunction structure was realized in the temperature range of 110–350 K (by step 30 K) at 1 MHz. The frequency-dependent reverse and forward bias C–V and G/ω$$-V$$ characteristics of the Au/SrTiO3/p-Si heterojunction structure was realized in the frequency range of 100–900 kHz (by step 100 kHz) at room temperature. It has been demonstrated that Au/SrTiO3/p-Si heterojunction structure exhibits negative capacitance (NC) behavior as a result of both temperature- and frequency-dependent capacitance measurements due to the reduction of interface charges, ionization states and series resistance in the forward bias voltage. In addition, it was shown that it exhibits an intersection point in the forward bias voltage of both temperature and frequency-dependent capacitance measurements. In temperature and frequency-dependent admittance spectroscopy measurements of Au/SrTiO3/p-Si heterojunction structure was observed NC phenomenon.

Intrinsic Capacitance of Molybdenum Disulfide.

The metallic, 1T polymorph of molybdenum disulfide (MoS2) is promising for next-generation supercapacitors due to its high theoretical surface area and density which lead to high volumetric capacitance. Despite this, there are few fundamental works examining the double-layer charging mechanisms at the MoS2/electrolyte interface. This study examines the potential-dependent and frequency-dependent area-specific double-layer capacitance (Ca) of the 1T and 2H polymorphs of MoS2 in aqueous and organic electrolytes. Furthermore, we investigate restacking effects and possible intercalation-like mechanisms in multilayer films. To minimize the uncertainties associated with porous electrodes, we carry out measurements using effectively nonporous monolayers of MoS2 and contrast their behavior with reduced graphene oxide deposited layer-by-layer on atomically flat graphite single crystals using a modified, barrier-free Langmuir-Blodgett method. The metallic 1T polymorph of MoS2 (Ca,1T = 14.9 μF/cm2) is shown to have over 10-fold the capacitance of the semiconducting 2H polymorph (Ca,2H = 1.35 μF/cm2) near the open circuit potential and under negative polarization in aqueous electrolyte. However, under positive polarization the capacitance is significantly reduced and behaves similarly to the 2H polymorph. The capacitance of 1T MoS2 scales with layer number, even at high frequency, suggesting easy and rapid ion penetration between the restacked sheets. This model system allows us to determine capacitance limits for MoS2 and suggest strategies to increase the energy density of devices made from this promising material.

Increased static dielectric constant in ZnMnO and ZnCoO thin films with bound magnetic polarons

A novel small signal equivalent circuit model is proposed in the inversion regime of metal/(ZnO, ZnMnO, and ZnCoO) semiconductor/Si3N4 insulator/p-Si semiconductor (MSIS) structures to describe the distinctive nonlinear frequency dependent capacitance (C-F) and conductance (G-F) behaviour in the frequency range from 50 Hz to 1 MHz. We modelled the fully depleted ZnO thin films to extract the static dielectric constant (εr) of ZnO, ZnMnO, and ZnCoO. The extracted enhancement of static dielectric constant in magnetic n-type conducting ZnCoO (εr ≥ 13.0) and ZnMnO (εr ≥ 25.8) in comparison to unmagnetic ZnO (εr = 8.3–9.3) is related to the electrical polarizability of donor-type bound magnetic polarons (BMP) in the several hundred GHz range (120 GHz for CdMnTe). The formation of donor-BMP is enabled in n-type conducting, magnetic ZnO by the s-d exchange interaction between the electron spin of positively charged oxygen vacancies {V}_{o}^{+} in the BMP center and the electron spins of substitutional Mn2+ and Co2+ ions in ZnMnO and ZnCoO, respectively. The BMP radius scales with the Bohr radius which is proportional to the static dielectric constant. Here we show how BMP overlap can be realized in magnetic n-ZnO by increasing its static dielectric constant and guide researchers in the field of transparent spintronics towards ferromagnetism in magnetic, n-ZnO.

GaN 2DEG Varactor-Based Impulse Suppression Module for Protection Against Malicious Electromagnetic Interference

A GaN-based metal–semiconductor–metal varactor with a two-dimensional electron gas (2DEG) layer is proposed and fabricated. The capacitance variation of this fabricated varactor biased at different external voltages is studied and measured, and the frequency-dependent capacitance and resistance of the varactor are simulated by a corresponding empirical formula. A high-frequency protective filter is further constructed and placed under a large pulsed-current injection in a malicious electromagnetic interference immunity test. The results show that the proposed GaN-based module can reduce the large pulsed current to an acceptably small level. Thus, the GaN-based 2DEG varactor is an attractive candidate for applications designed to protect the upcoming 5G high-frequency system from risks such as electrostatic discharge, lightning, and electromagnetic pulses.

Low Operating Voltage Organic Field-Effect Transistors with Gelatin as a Moisture-Induced Ionic Dielectric Layer: The Issues of High Carrier Mobility.

We have developed low-voltage (<2 V) flexible organic field-effect transistors (OFETs) with high carrier mobility using gelatin as a moisture-induced ionic gate dielectric system. Ionic concentration in the gelatin layer depends on the relative humidity condition during the measurement. The capacitance of the dielectric layer used for the calculation of field-effect carrier mobility for the OFETs crucially depends on the frequency at which the capacitance was measured. The results of frequency-dependent gate capacitance together with the anomalous bias-stress effect have been used to determine the exact frequency at which the carrier mobility should be calculated. The observed carrier mobility of the devices is 0.33 cm2/Vs with the capacitance measured at frequency 20 mHz. It can be overestimated to 14 cm2/Vs with the capacitance measured at 100 kHz. The devices can be used as highly sensitive humidity sensors. About three orders of magnitude variation in device current have been observed on the changes in relative humidity (RH) levels from 10 to 80%. The devices show a fast response with a response and recovery times of ∼100 and ∼110 ms, respectively. The devices are flexible up to a 5 mm bending radius.

Probing bias and power dependency of high-performance broadband Mg/ZnSnP2/Sn back-to-back Schottky junction photodetectors

Two non-identical Mg/ZnSnP2 and ZnSnP2/Sn Schottky diodes connected in coplanar back-to-back configuration are fabricated on p-type silicon (100) substrate for photodetection in the UV-VIS-NIR spectral region. A detailed study of the power and bias dependent responsivity, detectivity, and response and recovery speed of the devices is reported. The responsivity and detectivity were found to be 0.2 A W-1 and 4.62 × 1012 Jones for the Mg/ZnSnP2 and 0.03 A W-1 and 1.62 × 1011 Jones for the Sn/ZnSnP2 junctions, respectively when they were operated without bias. However, under a reverse bias of 2.5 V, these values changed to 4.7 A W-1 and 1.19 × 1012 Jones in the case of Mg/ZnSnP2 and 12.7 A W-1 and 4.78 × 1011 Jones for Sn/ZnSnP2 junctions, respectively. The photocurrents associated with both the junctions were increased superlinearly with illumination power which is correlated to the conversion of the existing traps within the forbidden energy gap to the recombination centers. The response and recovery speed of the photodetectors were also studied under variable bias and illumination power. Under an incident power of 0.34 mW, the rise and decay times for the Mg/ZnSnP2 and Sn/ZnSnP2 junctions were 200 μs, 2300 μs and 390 μs, 240 μs, respectively at 2.5 V. The Mg/ZnSnP2 showed an anomalous bias dependent secondary decay channel which disappeared at self-powered configuration. The frequency-dependent capacitance in the dark and illumination power-dependent capacitance of the structure were also performed to understand the presence of defect states and the capture of photogenerated carriers by the traps and recombination centers.

Influence of Metal Gate Electrodes on Electrical Properties of Atomic-Layer-Deposited Al-Rich HfAlO/Ga2O3 MOSCAPs

As the p-type doping $\beta $ -Ga2O3 is absent up to now, metal gate (MG) stacks with high work functions are expected to benefit the fabrication of normally- OFF $\beta$ -Ga2O3 transistors. In this article, the electrical characteristics of $\beta $ -Ga2O3 metal-electrode-gated metal–oxide–semiconductor (MOS) devices with Al-rich HfAlO dielectrics and different MG stacks (Ni, Au, Pt, and Ti) are evaluated. The interface state density ( ${D}_{\text {it}}$ ) of HfAlO/ $\beta $ -Ga2O3 interface is characterized based on the frequency-dependent capacitance–voltage ( ${C}{-}{V}$ ) and photo-assisted deep ultraviolet (DUV) ${C}{-}{V}$ measurements. An average $D_{\text {it}}$ of ${4.45}\times {10}^{{11}}$ eV $^{-{1}}$ cm $^{-{2}}$ is extracted from the photo-assisted (deep UV) ${C}{-}{V}$ measurement, while a large amount of border traps, negative fixed charges, and deep traps is also induced at the oxide layer and/or HfAlO/ $\beta $ -Ga2O3 interface. Then, this article investigates the evaluations of Ti, Ni, Au, and Pt as candidate MGs for $\beta $ -Ga2O3 MOS using Al-rich HfAlO as gate dielectric. The obvious flat-band voltage ( $V_{\text {FB}}$ ) shift and gate leakage variation are observed in $\beta $ -Ga2O3 capacitors with different MG solutions, indicating that HfAlO dielectric combined with Ni, Au, and Pt MGs is promising to facilitate some beneficial modifications of normally- OFF $\beta$ -Ga2O3 transistors, while Ti electrode is more suitable for normally- ON $\beta$ -Ga2O3 transistors. This article provides an additional practical guideline for choosing the appropriate MG stacks and potential gate dielectric to the development of normally-OFF Ga2O3 transistors.

Determination of current transport and trap states density in AlInGaN/GaN heterostructures

The energy distribution and the relaxation time constant of the trap states with respect to conduction bands in the (Ni/Au) Schottky contact on AlInGaN/GaN heterostructures were investigated using the admittance technique. The potential dependent capacitance/conductance measurements were done in the frequency range of 5 kHz to 5 MHz at a temperature of 300 K. We found strong frequency dispersions at the accumulation regions and at the sharp transition regions (depletion region) in the capacitance curves. High frequency dispersion at the accumulation regions in C-V characteristics indicates that there is a high-density of surface traps between the metal–AlInGaN quaternary layer interfaces. Furthermore, the frequency dispersion at the sharp transition regions behavior can be attributed to the interface traps state between the AlInGaN quaternary layer and GaN layer. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming the models in which traps are located between the metal–AlInGaN interface (surface traps) and between AlInGaN/GaN interfaces (interface traps). The trap states density and time constants of the traps states were calculated as a function of energy separation from the conduction-band edge. The trap states' densities change between 1.3 × 1011 eV−1 cm−2 and 6.2 × 1011 eV−1 cm−2. Also, 4.8 to 5.3 μs time interval calculated for the relaxation times.

Enhanced functionalities of DNA thin films by facile conjugation with conducting polymers

In this study, we discuss a method to embed PEDOT:PSS into DNA with a designated concentration of PEDOT:PSS and construction of PEDOT:PSS-embedded DNA thin films. In order to shed light on the interaction between PEDOT:PSS and DNA, optical spectroscopy measurements were performed. DNA-PEDOT:PSS thin films showed a broad absorption band around 800 nm which was associated with PEDOT:PSS. The electrical properties of DNA-PEDOT:PSS thin films were assessed. A significant enhancement in current for DNA-PEDOT:PSS thin films DNA was observed which agreed with the decrement in band gap of DNA-PEDOT:PSS thin films. For the energy storage capability and dielectric constant of DNA-PEDOT:PSS thin films, capacitance measurements were conducted. Frequency-dependent capacitance indicated enhancement in the capacitance and dielectric constant by electric polarization of PEDOT:PSS in a DNA thin film. Our approach may assist in development of various biosensors and electronic devices with specific functionalities based on biomaterials and conducting polymer complexes.

Ultra-wide bandgap AlGaN metal oxide semiconductor heterostructure field effect transistors with high-k ALD ZrO2 dielectric

We report on Al0.65Ga0.35N/Al0.4Ga0.6N metal oxide semiconductor heterojunction field-effect transistor (MOSHFET) with high-k ZrO2 gate-dielectric deposited using atomic layer deposition process. As extracted from frequency dependent capacitance–voltage (CV) characteristics, the oxide gates resulted in an interfacial state trap density of ∼2 × 1012 cm−2. A comparative study, on the same material, shows the gate-leakage current of the ZrO2 MOSHFETs to be lower by five orders; their ON/OFF current ratio (∼107) to be higher by about four orders and their threshold voltage to decrease (less negative) by 3.5 V with respect to the Schottky gate devices.