Metal-insulator-semiconductor Devices Research Articles

Diamond-like carbon as gate dielectric for metal–insulator–semiconductor applications

Diamond-like carbon (DLC) has been studied as a dielectric material for future metal–insulator–semiconductor (MIS) technology. In this paper, ultrathin DLC films were deposited on silicon substrates by using the dc magnetron sputtering technique at various deposition voltages. The current–voltage characteristics indicated that the leakage currents of the MIS devices decreased with an increase in deposition voltages, and that a low leakage current ([Formula: see text] A/cm2) was achieved at −2 V bias voltage. The deposition voltage effects on the structures of films were investigated through Raman spectroscopy, which indicated that the sp3 bonding fraction decreased with an increase in the deposition voltage. The ramp-voltage breakdown test revealed high effective breakdown electric field ([Formula: see text]85 MV/cm) for the MIS device with the DLC film deposited at 1100-V deposition. Stress-induced leakage current measurement indicated that the DLC film exhibited excellent reliability.

AN ASSESSMENT ON ELECTRICAL CHARACTERIZATION OF Ni/n-Si SCHOTTKY RECTIFIERS WITH AND WITHOUT Ta2O5 INTERFACIAL OXIDE LAYER

We have fabricated Ni/[Formula: see text]-Si metal–semiconductor (MS) and Ni/Ta2O5/[Formula: see text]-Si metal-insulator–semiconductor (MIS) Schottky barrier diodes at room temperature and studied their current density–voltage (J–V) and capacitance–voltage (C–V) characteristic properties. The forward bias J–V characteristics of the fabricated MS and MIS devices have been evaluated with the help of the thermionic emission (TE) mechanism. Schottky barrier height (SBH) values of 0.73 and 0.84[Formula: see text]eV and ideality factor values of 1.75 and 1.46 are extracted using J–V measurements for MS and MIS Schottky barrier diodes without and with Ta2O5 interfacial oxide layer, respectively. It was noted that the incorporation of Ta2O5 interfacial oxide layer enhanced the value of SBH for the MIS device because this oxide layer produced the substantial barrier between Ni and [Formula: see text]-Si and this obtained barrier height value is better than the conventional metal/[Formula: see text]-Si (MS) Schottky diodes. The rectification ratio (RR) calculated at [Formula: see text][Formula: see text]V for the MS structure is found to be [Formula: see text] and the MIS structure is found to be [Formula: see text]. Using Chung’s method, the series resistance ([Formula: see text]) values are calculated using [Formula: see text]/[Formula: see text] vs I plot and are found to be 21,603[Formula: see text][Formula: see text] for the Ni/[Formula: see text]-Si (MS) and 5489[Formula: see text][Formula: see text] for the Ni/Ta2O5/[Formula: see text]-Si (MIS) structures, respectively. In addition, [Formula: see text] vs [Formula: see text] plot has been utilized to evaluate the series resistance ([Formula: see text]) values and are found to be 14,064[Formula: see text][Formula: see text] for the Ni/[Formula: see text]-Si (MS) and 2236[Formula: see text][Formula: see text] for the Ni/Ta2O5/[Formula: see text]-Si (MIS) structures, respectively. In conclusion, by analyzing the experimental results, it is confirmed that the good quality performance is observed in Ni/Ta2O5/[Formula: see text]-Si (MIS) type SBD when compared to Ni/[Formula: see text]-Si (MS) type SBD and can be accredited to the intentionally formed thin Ta2O5 interfacial oxide layer between Nickel and [Formula: see text]-type Si.

Novel high-k gate dielectric properties of ultrathin hydrocarbon films for next-generation metal-insulator-semiconductor devices

New high-k gate dielectrics are highly necessary in facilitating the continuous down-scaling of metal–oxide–semiconductor devices to the sub-10 nm range. This study presents ultrathin organic hydrocarbon (HC) films as a novel high-k gate insulator for metal–insulator–semiconductor (MIS) devices. During inductively-coupled plasma chemical vapor deposition with CH4 and H2 gases, the growth temperature greatly affects the structure of the carbon layers and consequently their dielectric characteristics. Specifically, sp2-rich dielectric HC layers are formed below 600 °C, whereas highly-ordered sp2-hybridized graphene is formed at 950 °C. The k value of the resulting HC films increases up to a maximum value of 90 at 350 °C. Moreover, the MIS devices exhibit excellent gate-insulating properties, including almost no hysteresis in the capacitance–voltage curve, low leakage current, and high dielectric strength, which surpass those of existing high-k gate oxides. These results reveal that the organic HC films are a promising next-generation high-k gate dielectric material for sub-10 nm node Si and organic semiconductor technologies.

Effect of rare-earth Pr6O11 insulating layer on the electrical properties of Au/n-GaN Schottky electrode and its chemical and structural characterization

An Au/Pr6O11/n-GaN metal/insulator/semiconductor (MIS) junction was prepared with a high-k praseodymium oxide insulator layer and probed its structural, chemical and electrical characteristics by XRD, TEM, XPS, I–V and C–V approaches. XRD, TEM and XPS examinations confirm the Pr6O11 film growth on n-type GaN surface. Electrical results demonstrate the fabricated junctions show a good rectifying nature with a low leakage current. The series resistance (RS) and shunt resistance (RSh) were derived for the Au/n-GaN Schottky electrode (SE) and MIS junction. MIS junction possesses a higher barrier height (BH) compared to the Au/n-GaN SE, implying the insulator layer altered the BH. By employing Cheung’s, Norde and surface potential plots, the BH, ideality factor and RS were evaluated and the results were comparable. Lower interface state density (NSS) was obtained for the MIS junction than the SE, which confirmed that the Pr6O11 insulator layer plays a vital role in lowering the NSS. Results demonstrated the Poole–Frenkel emission controls the current conduction mechanism in reverse-bias of both SE and MIS junction. Observations stated that the Pr6O11 thin film is a suitable high-k insulating material for the fabrication of GaN-based MIS devices.

Threshold voltage extraction for organic thin film transistor in linear region using asymmetric metal insulator semiconductor capacitive test structure

Metal Insulator Semiconductor (MIS) capacitors are commonly used as a test structure for characterization of semiconductor/insulator interface. However, MIS devices do not provide useful information in strong accumulation or inversion mode as the capacitance saturates to a constant value. An MIS capacitor with area asymmetry on the other hand, exhibits a gate voltage dependent capacitance in strong accumulation mode and can be used to obtain additional useful information about the semiconductor/insulator interface. The present work describes the use of asymmetrical metal–insulator–semiconductor device for characterization of the threshold voltage in metal–insulator–organic test structures. Simulation results are presented to show that the threshold voltage extracted from these devices not only matches with that extracted from current–voltage characteristics of organic thin film transistors in the linear region but is also much less sensitive to source contact resistance. The experimental results obtained with pentacene as active semiconductor and poly-vinyl-phenol as the dielectric are also presented to demonstrate the operation and merits of the proposed technique.

Improvement of the storage ability of Si-rich oxide layer in poly-Si based nonvolatile memory devices by implementation of taguchi method

The storage ability of silicon-rich silicon oxide (Si-rich SiOx) floating gates plays a critical role in poly-Si nonvolatile memory devices. In this study, the Taguchi method, a statistical means of experimental design which allows for the optimization of the storage characteristics with a dramatic reduction in the number of experiments by approximately 90%, is used. The memory window of the metal insulator semiconductor devices is used as a figure of merit to find out the optimal process parameters. Furthermore, the analysis of variance showed that the substrate temperature is the dominant factor affecting the memory characteristics of the SiOx storage layers. A significant improvement in the performance of poly-Si nonvolatile memory devices using the optimal Si-rich SiOx as a charge storage layer was observed. These devices show retention of the threshold voltage shift exceeding ∼98% after 104 s and ∼96% after 10 years extrapolation with programming/erasing voltages of −12 V/+11 V at a low duration of 1 μs. Therefore, the poly-Si based nonvolatile memory devices using Si-rich SiOx as a storage layer show a high potential for memory system applications.

High Quantum Efficiency Hot Electron Electrochemistry.

Using hot electrons to drive electrochemical reactions has drawn considerable interest in driving high-barrier reactions and enabling efficient solar to fuel conversion. However, the conversion efficiency from hot electrons to electrochemical products is typically low due to high hot electron scattering rates. Here, it is shown that the hydrogen evolution reaction (HER) in an acidic solution can be efficiently modulated by hot electrons injected into a thin gold film by an Au-Al2O3-Si metal-insulator-semiconductor (MIS) junction. Despite the large scattering rates in gold, it is shown that the hot electron driven HER can reach quantum efficiencies as high as ∼85% with a shift in the onset of hydrogen evolution by ∼0.6 V. By simultaneously measuring the currents from the solution, gold, and silicon terminals during the experiments, we find that the HER rate can be decomposed into three components: (i) thermal electron, corresponding to the thermal electron distribution in gold; (ii) hot electron, corresponding to electrons injected from silicon into gold which drive the HER before fully thermalizing; and (iii) silicon direct injection, corresponding to electrons injected from Si into gold that drive the HER before electron-electron scattering occurs. Through a series of control experiments, we eliminate the possibility of the observed HER rate modulation coming from lateral resistivity of the thin gold film, pinholes in the gold, oxidation of the MIS device, and measurement circuit artifacts. Next, we theoretically evaluate the feasibility of hot electron injection modifying the available supply of electrons. Considering electron-electron and electron-phonon scattering, we track how hot electrons injected at different energies interact with the gold-solution interface as they scatter and thermalize. The simulator is first used to reproduce other published experimental pump-probe hot electron measurements, and then simulate the experimental conditions used here. These simulations predict that hot electron injection first increases the supply of electrons to the gold-solution interface at higher energies by several orders of magnitude and causes a peaked electron interaction with the gold-solution interface at the electron injection energy. The first prediction corresponds to the observed hot electron electrochemical current, while the second prediction corresponds to the observed silicon direct injection current. These results indicate that MIS devices offer a versatile platform for hot electron sources that can efficiently drive electrochemical reactions.

Comparative Study Between Partially and Fully Recessed‐Gate Enhancement‐Mode AlGaN/GaN MIS HEMT on the Breakdown Mechanism

In this paper, two enhancement‐mode (E‐mode) AlGaN/GaN recessed‐gate MIS devices with the in situ N2 plasma treatment, known as partially recessed‐gate metal insulator semiconductor (MIS) device and fully recessed‐gate MIS device, are designed. Among them, the partially recessed‐gate MIS device shows excellent characteristics that the threshold voltage of +3.5 V, saturation current density of 722 mA mm−1, peak transconductance of 212 mS mm−1, and the power figure of merit of 4.39 × 108 W cm−2 which is the highest value in E‐mode AlGaN/GaN MIS device with the threshold voltage greater than 3 V. Moreover, the current collapse and breakdown voltage of partially recessed‐gate MIS device and fully recessed‐gate MIS device are investigated, and Silvaco simulation is carried out to analyze the difference of breakdown mechanism between two structure devices. Through the analysis of five main breakdown leakage paths, we can get the conclusion that the factor causing the breakdown voltage difference between partially recessed‐gate MIS device and fully recessed‐gate MIS device is the difference in the width of depletion region of the two devices.

MIS-TSC: A combination of the thermally stimulated current method and a metal-insulator-semiconductor device for unipolar trap spectroscopy

To determine the density of states distribution of traps within a semiconductor, the thermally stimulated current (TSC) method is often applied. However, the bipolar nature of the typical device structure does not allow for strict unipolar operation, and therefore the method does not allow for the separate evaluation of electron and hole traps. The recombination between electrons and holes makes the interpretation of the data difficult, which becomes an essential drawback of this method. To address these issues, we propose the use of a metal insulator semiconductor (MIS) device structure for TSC measurements, which can be operated strictly unipolar by the sign of the applied voltage during the charging process. Thus, the problem of recombination and bipolar contribution to the measurement signal is avoided. As an additional benefit, the MIS device structure typically results in very low leakage currents, and thus a low noise level for the measurement. This permits precise measurements even below 1 pA, and consequently increases the resolution of the method. This aspect is especially important for fractional TSC, as the measurement time is long and the current low when compared to the envelope measurement. Here, we demonstrate the basic principle of this TSC approach, which we name MIS-TSC, using the well-studied organic semiconductor P3HT as a benchmark.

Trap state characterization of Al2O3/AlInGaN/GaN metal-insulator-semiconductor heterostructures

Frequency-dependent conductance measurements were carried out to investigate the trap states in Al2O3/AlInGaN/GaN metal-insulator-semiconductor (MIS) heterostructures. From the electrical measurements, an improvement in trap state characteristics was observed for the device fabricated with lower In composition in quaternary nitride layers. In the presence of higher In composition, segregation of In atoms was observed in AlInGaN layers. Because of this In-segregation, surface quality of the quaternary-N deteriorated that led to the formation of trap states at and near the oxide/semiconductor interface. Therefore, in the presence of lower In composition, an improvement in trap characteristics was observed for the AlInGaN/GaN-based MIS devices.

Understanding the electrostatics of top-electrode vertical quantized Si nanowire metal–insulator–semiconductor (MIS) structures for future nanoelectronic applications

In this paper, a comprehensive analysis of the electrostatics of top-electrode vertically aligned quantized Si nanowire metal–insulator–semiconductor (MIS) structure is performed by formulating a self-consistent analytical model with simultaneous solution of Schrodinger and Poisson equations. The impact of high-k dielectrics on the electrostatic control of such quantized nanowire MIS devices is studied in detail. The electrostatic control is observed to degrade significantly for such high-k insulators with identical equivalent oxide thickness (EOT) due to the nonlinear dependence between dielectric constant and EOT in quantized nanowire MIS devices. The distribution of 3D confined charges along the nanowire is primarily governed by the generated quantum states which are a nonlinear function of the applied voltage. The electrostatic integrity of such device is investigated in terms of simultaneously maintaining the electrostatic control and reduction in carrier tunneling probability. In this context, the impact of several controlling parameters such as applied voltage, barrier height of the insulator/semiconductor junction, carrier effective mass of the insulator and nanowire diameter on tunneling probability is examined. The results suggest insulator effective mass (high-m*) to be the more significant parameter for maintaining electrostatic integrity than its dielectric constant (high-k) in quantized nanowire top-electrode MIS devices.

Ultrasensitive Gas Sensors Based on Vertical Graphene Nanowalls/SiC/Si Heterostructure.

Gas sensors, which play an important role in the safety of human life, cover a wide range of applications including intelligent systems and detection of harmful and toxic gases. It is known that graphene is an ideal and attractive candidate for gas sensing due to its high surface area and excellent mechanical, electrical, optical, and thermal properties. However, in order to fully realize its potential as a commercial gas sensor, demand for a graphene-based device of low-limit detection, high sensitivity, and fast response time needs to be met. Here, we demonstrate a metal/insulator/semiconductor (MIS) based gas sensor consisting of as-grown epitaxial graphene nanowalls (EGNWs)/silicon carbide (SiC)/silicon (Si) structure. The unique edge dominant three-dimensional (3D) EGNWs based MIS device achieved an extraordinarily low limit of detection (0.5 ppm) and unprecedented sensitivity (82 μA/ppm/cm2 for H2) with a fast response of shorter than 500 ms. These unique properties of our MIS device are attributed to the abundance of vertically oriented nanographitic edges and structural defects that act as extra-favorable adsorption sites and exhibit fast electron-transfer kinetics through the edges. Our experimental findings can pave the way for the realization of high-performance 3D graphene-based gas sensor devices.

Effect of Oxide Thickness on The Two-State Characteristics in MIS(p) Tunnel Diode with Ultrathin Metal Surrounded Gate

In this work, the transient two-state currents of ultrathin metal surrounded gate (UTMSG) metal-insulator-semiconductor (MIS) tunnel diodes, in which the periphery portion of the gate metal thickness is about 10 nm, with various oxide thicknesses were studied. The electrical characteristics and transient two-state characteristics in the UTMSG MIS and the regular gate metal-insulator-semiconductor (RG MIS) tunnel diodes with various oxide thicknesses were compared and it was found that the UTMSG MIS devices can maintain larger two-state current window within appropriate oxide thicknesses range of 27 Å ∼ 30 Å. The electrical properties of the UTMSG MIS devices are very sensitive to oxide thickness. Also, it was found that the I-V current hysteresis is closely related to the transient two-state characteristics because of the RC delay at edge.

The current–voltage and capacitance–voltage characterization of the Au/Methylene Blue/n-GaAs organic-modified Schottky diodes

We report the electrical properties of the Au/n–GaAs devices with and without thin organic interface layer. Methylene blue (MB) is a heterocyclic aromatic chemical compound with the molecular formula C16H18N3SCl. The MB layer was formed by spin coating technique on chemically cleaned gallium arsenide (GaAs) substrate. The current–voltage (I–V) and the frequency dependent capacitance–voltage (C–V) characteristics of the Au/MB/n–GaAs metal-insulator-semiconductor (MIS) and Au/n–GaAs metal-semiconductor (MS) devices have been investigated at room temperature. The MS and MIS devices I–V characteristics the showed a good rectification, and they were analyzed based on the thermionic emission (TE) theory. The ideality factor (n) and the barrier height (Φb(IV)) from the I–V characteristics was determined as 1.131±0.006 and 0.782±0.005 eV for MS device and 1.336±0.057 and 0.950±0.008 eV for MIS device, respectively. A Cheung’s method and modified Norde's function has been used to extract the parameters including the (Φb) and the series resistance (RS). Also the values of the barrier height obtained from the C–V measurements (Φb(CV)) of the MS and MIS was 0.863±0.034 eV and 1.187±0.093 eV, at 1 MHz, respectively.Distributions of the interface state density (Dit) of the MS and MIS devices were derivate from I–V and C–V measurements. Our results indicates that the Au/MB/n–GaAs device had lower interface state density values than the Au/GaAs device. Also non-saturated reverse bias current investigated by the using a Pole-Frenkel emission model. Furthermore, the optical and morphological properties of MB layer were investigated by the Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and UV-vis Spectrophotometer (UV-vis).Finally, we showed that, increasing Φb and decreasing Dit and improving electrical parameters of MIS devices indicates that, thin MB interface layer could prefer for modification of Au/n–GaAs devices.

Modulation of the Charge of Germanium MIS Structures with Fluorine-Containing Insulators

An insulator layer of ErF3, YF3, NdF3, and TmF3 was formed in n-type Ge-based MIS (metal–insulator–semiconductor) structures. It is shown that no negative effective charge is observed in these Ge MIS structures, while the degradation of electric characteristics and the rise of density of surface states leads to an increase in the positive charge. The positive charge formed at the Ge–rare-earth-element fluoride interface can compensate the negative charge of dangling bonds on the surface of Ge, which is potentially promising for modulation of the charge magnitude and sign in MIS devices based on Ge.

Gate modeling of metal–insulator–semiconductor devices based on ultra-thin atomic-layer deposited TiO2

Metal–insulator–semiconductor devices having different oxide thicknesses (10, 6, 4 and 2 nm) were fabricated using atomic-layer deposited ultra-thin amorphous TiO2 as gate dielectric. From Ig–Vg measurements it was determined that the main conduction mechanism is Schottky emission for all thicknesses and even after passivation of the semiconductor–insulator interface using SiOx. Furthermore, the Schottky barrier height (ΦB) increases when the oxide thickness decreases; this was further corroborated using semi empirical models and SILVACO simulations having excellent agreement. From this analysis, important physical parameters like barrier height (ΦB), effective mass (m*) and optical dielectric constant (er) were extracted, and could be used to effectively understand the performance and reliability of these devices. From the extraction of physical parameters associated to the conduction mechanism, a correlation between materials’ properties with device performance could be obtained (higher barrier height (ΦB) would result in a decrease in leakage current). Also, the high reproducibility enables enhanced performance and therefore, better reliability predictions for electron devices based on these oxides.

Parameter extraction of gate tunneling current in metal–insulator–semiconductor capacitors based on ultra-thin atomic-layer deposited Al2O3

Metal–insulator–semiconductor devices were fabricated using ultra-thin (6 nm) atomic layer deposited Al2O3. From Ig–Vg measurements, it was determined that the main conduction mechanisms for these devices are Ohmic conduction at very low electric fields (E 2 MV cm−1) and finally, just before breakdown, Fowler–Nordheim (E > 5 MV cm−1). From the accurate verification of these conduction mechanisms, physical parameters such as barrier height (ΦB), effective mass (m*) and energy trap level (ΦT) are extracted and could be used to effectively understand the performance and reliability of these devices under different substrate injection conditions.

Effect of Si3N4‐Mediated Inversion Layer on the Electroluminescence Properties of Silicon Nanocrystal Superlattices

AbstractThe achievement of an efficient all‐Si electrically‐pumped light emitter is a major milestone in present optoelectronics still to be fulfilled. Silicon nanocrystals (Si NCs) are an attractive material which, by means of the quantum confinement effect, allow attaining engineered bandgap visible emission from Si by controlling the NC size. In this work, SiO2‐embedded Si NCs are employed as an active layer within a light‐emitting device structure. It is demonstrated that the use of an additional thin Si3N4 interlayer within the metal–insulator–semiconductor device design induces an enhanced minority carrier injection from the substrate, which in turn increases the efficiency of sequential carrier injection under pulsed electrical excitation. This results in a substantial increase in the electroluminescence efficiency of the device. Here, the effect of this Si3N4 interlayer on the structural, optical, electrical, and electro‐optical properties of a Si NC‐based light emitter is reported, and the physics underlying these results is discussed.

Stress induced degradation and reliability of Al2O3 thin film on silicon

The electrical properties of metal insulator semiconductor (MIS) devices with Al2O3 as dielectric layer deposited by reactive RF (radio frequency) magnetron sputtering were investigated using Capacitance-Voltage (C-V) and Current–Voltage (I-V) to determine the quality of oxide layer and oxide/silicon interface. To assess the reliability of Al2O3/Si interface constant current stress of 1 mA for varying time period was also investigated. The effect of post deposition annealing (PDA) on electrical behavior of Al/Al2O3/Si MOS (metal oxide semiconductor) capacitors was studied. Annealed devices show substantial improvement in interface trap charge density (Dit), fixed oxide charge density (Qf) and leakage current. Improved electrical and interface properties are achieved at annealing temperature of 425 °C. Incorporation of nitrogen gas improves the thermal stability of Al2O3 films which exhibited fewer shift in flat band voltage (Vfb) as compared to the samples grown in pure argon atmosphere. Breakdown voltage for nitrogen doped Al2O3 of 30 nm thin films was enhanced from 15 V to 19 V. Results indicate that reactive sputtering in N2 containing plasma is a promising approach as reduction in gate leakage current and power dissipation is utmost essential for integrating high-k material into semiconductor processing.

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.