MIS Diodes Research Articles

Preparation and Characterization of Deposited Tetraethylorthosilicate-SiO<sub>2</sub>/SiC MIS Structure

The SiO2 layer was deposited on the 4H-SiC Si face by the thermal decomposition of tetraethylorthosilicate(TEOS) in N2 atmosphere to from MIS diodes. The post deposition annealing was effective to improve the interface properties. The interface state density of the deposited SiO2/SiC MIS structure was estimated to be the order of 1011 cm-2eV-1 by Terman method. The direct nitridation of SiC surface prior to the deposition of the SiO2 layer was effective to reduce the interface state density.

Interface states in metal-insulator-semiconductor Pt-GaN diode hydrogen sensors

Exposure of Pt-SiO2-GaN metal-insulator-semiconductor (MIS) diodes to hydrogen at room temperature is found not only to shift the flat-band voltage toward negative bias values as compared with that in nitrogen, which results in significant sensitivity of the devices to hydrogen, but also to reduce the interface state density (Dit) dramatically for the first time. Pt-SiO2-GaN MIS diodes in nitrogen yields the Dit of ∼8 × 1011 cm−2 eV−1 at 0.4 eV from the conduction band edge (Ec), and hydrogen exposure reduces the Dit by more than one order of magnitude to the low 1010 cm−2 eV−1 range. In sharp contrast to Pt-SiO2-GaN MIS diodes, neither flat-band voltage shift nor Dit (∼1 × 1013 cm−2 eV−1 at 0.4 eV) reduction is observed for Pt-SixNy-GaN MIS diodes upon hydrogen exposure. These results suggest that atomic hydrogen interacts with MIS interface in Pt-SiO2-GaN MIS diodes even at room temperature. In addition, hydrogen treatment would be a promising method in order to reduce the Dit in GaN metal-oxide-semiconductor field-effect transistors using SiO2 as the gate dielectric, leading to the mobility enhancement of the devices.

Effects of illumination on electrical parameters of Ag/n-CdO/p-Si diode

The current–voltage (I–V) characteristics of the Ag/n-CdO/p-Si diode were investigated under various white light (visible light) illuminations. The electrical parameters such as ideality factor (n), zero-bias-barrier height (Φb) and series resistance (RS) of Ag/n-CdO/p-Si MIS diodes were determined by using the forward bias current–voltage measurements. The Ag/n-CdO/p-Si diode exhibits a non-ideal behavior due to the interfacial layer, the interface states and the series resistance. The ideality factor is increased, while the barrier height is decreased with decreasing illumination intensities. The values of RS obtained from Cheung and Norde methods are decreased with increasing illumination intensity. The distribution profile of the interface states (NSS) as a function of energy distribution (ESS − EV) was extracted from the forward I–V measurements under various illumination intensities. The interface state densities were observed to be strongly illumination dependent and are decreased with increasing illumination intensities.

Integration of high-dielectric constant Ta2O5 oxides on diamond for power devices

The authors report on the direct integration of high-dielectric constant (high-k) Ta2O5 films on p-type single crystal diamond for high-power electronic devices. Crystallized hexagonal phase δ-Ta2O5 film is achieved on diamond by annealing the amorphous Ta2O5 film deposited by a sputter-deposition technique. The electrical properties of the Ta2O5 thin films are investigated by fabricating metal-insulator-semiconductor (MIS) diodes. The leakage current of the MIS diode is as low as 10−8 A/cm2 for the as-deposited amorphous Ta2O5 film and 10−2 A/cm2 for the crystallized film, which is 108 and 102 times lower than that of the Schottky diode at a forward bias of −3 V, respectively. The dielectric constant of the amorphous Ta2O5 films is measured to be 16 and increases to 29 after annealing at 800 °C. Different current leakage mechanisms and charge trapping behaviors are proposed for the amorphous and crystallized Ta2O5 thin films.

Effect of Direct Nitridation of 4H-SiC Surface on MOS Interface States

A nitride layer was formed on a SiC surface by direct nitridation in pure N2 or in NH3 diluted with N2. The SiO2 layer was deposited by the thermal decomposition of tetraethylorthosilicate (TEOS) on the nitride layer to form an MIS diode. The XPS analysis showed that the nitride layer was oxidized during the deposition process of SiO2. The direct nitridation was effective to reduce the interface state density between the insulating layer and 4H-SiC

Characterization of Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs by quasi‐static C‐V measurement

AbstractThe threshold‐voltage (Vth) instability in AlGaN/GaN MIS‐HEMTs with ALD‐Al2O3 (15 nm) as gate dielectrics is systematically investigated by dc current‐voltage (I‐V), high‐frequency capacitance‐voltage (C‐V) (HFCV), and quasi‐static C‐V (QSCV) characterizations. For Al2O3/GaN/AlGaN/GaN MIS diodes, tiny Vth hysteresis (ΔVth) appears in double‐mode (up and down sweep) HFCV measurements if the maximum forward bias (VF,max) is only set to 0 V, while an apparent clockwise ΔVth (as large as 0.9 V) emerges as VF,max is increased to +5 V. The stability of Vth in the corresponding MIS‐HEMTs is thus studied by increasing the maximum VGS (VGS,max) in the measurement of double‐mode transfer characteristics. Significant clockwise ΔVth also occurred once the VGS,max exceeds +1.1 V, and it increased to ∼1 V at VGS,max= +3 V. Such Vth‐instability is absent in AlGaN/GaN HEMTs. It is suggested that the acceptor‐like deep states at Al2O3/GaN interface account for the Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs, and their filling and emission processes are successfully captured by QSCV measurements. The interface state density detected is about 4.6×1012 cm‐2 using 1 Hz QSCV. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Two-Step Polarization Reversal Process in Pentacene/Poly(vinylidene fluoride–trifluoroethylene) Double-Layer Capacitor: Reduced Coercive Field

The coercive field Ec of ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] has been studied by observing the displacement current due to polarization reversal. Unlike in a metal–insulator–metal device, the polarization reversal in a metal–insulator–semiconductor diode (pentacene as the semiconductor) is a two-step process. We used modified current–voltage measurements to intentionally avoid the second-step polarization reversal and observed a reduced Ec. The reduction of Ec is interpreted to be a result of the reduced local dipole-induced field, on the basis of the optical electric-field-induced second-harmonic generation measurements.

Deposition of TaN Films by RF Sputtering and Their Barrier Properties in Cu/TaN/Dielectrics/Si MIS Structures

The electrical resistivity and the barrier property of Tantalum nitride (TaN) thin films were systematically investigated as a function of annealing temperature using two different types of MIS structures of TaN/SiO2/Si and Cu/TaN/dielectric/Si(100), where either the thermally grown SiO2 (th-SiO2) or spin-on dielectric (SOD) hydrogen silsesquioxane (HSQ) films was used as a dielectric layer. We observed that the resistivity of TaN thin films before Cu deposition became lower with the growth of TaN(200) as compared with the growth of TaN(111) and TaN(220). Cu diffusion barrier properties of MIS diodes with TaN films were improved up to 500°C for both dielectric films due presumably to the decrease in sputter damage of dielectric films by annealing, while those without TaN thin films were degraded due to the diffusion of Cu into the dielectric films. The oxygen desorption from dielectric films and the oxidation of TaN films due to the reverse-sputtering of dielectric films during the sputtering of Ta in N2 is possible model of sputter damage. [DOI: 10.1380/ejssnt.2012.107]

Electrical transport properties of Au/SiO2/n-GaN MIS structure in a wide temperature range

The temperature-dependent electrical properties of Au/SiO2/n-GaN metal-insulator-semiconductor (MIS) structure have been investigated in the temperature range of 120–390 K. Anomalous strong temperature dependencies of the barrier height (Φbo), ideality factor (n), interface state density (NSS) and series resistance (RS) are obtained. Such behaviour is attributed to barrier inhomogeneities by assuming a Gaussian distribution of barrier heights (GD BHs) at the interface. It is evident that the diode parameters such as zero-bias barrier height increases and the ideality factor decreases with increasing temperature. The values of series resistance that are obtained from Cheung’s method is decreasing with increasing in temperature. The temperature-dependent current–voltage characteristics of the MIS diode have been shown a double Gaussian distribution giving mean barrier heights of 0.38 eV and 1.06 eV and standard deviations of 0.0561 and 0.2742 V, respectively. A modified ln (Io/T2) − q2σo2/2k2T2 versus 103/T plot for the two temperature regions gives φbo¯ and A∗ as 0.55 eV and 11.56 A cm−2 K−2, and 1.02 eV and 23.48 A cm−2 K−2 respectively. The Interface state density values are calculated by I–V and C–V measurements at different temperatures using Terman’s method. It is observed that the interface state density decreases with increase in temperature (120–390 K). Therefore, it has been concluded that the temperature dependence of the forward I–V characteristics of the Au/SiO2/n-GaN Schottky diodes can be explained with a double GD of the BHs.

Threshold Voltage Instability in Al2O3/GaN/AlGaN/GaN Metal–Insulator–Semiconductor High-Electron Mobility Transistors

The threshold voltage (Vth) instability in GaN-based metal–insulator–semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current–voltage (I–V), high-frequency capacitance–voltage (C–V) (HFCV), and quasi-static C–V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (<10 mV) in double-mode (up and down sweep) HFCV characteristics as the maximum forward bias (VFmax) during the sweep is set to 0 V, while an apparent ΔVth (as large as 0.9 V) emerges as VFmax is increased to +5 V for the MIS diode. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques.

Characterization of high-κ LaLuO3 thin film grown on AlGaN/GaN heterostructure by molecular beam deposition

We report the study of high-dielectric-constant (high-κ) dielectric LaLuO3 (LLO) thin film that is grown on AlGaN/GaN heterostructure by molecular beam deposition (MBD). The physical properties of LLO on AlGaN/GaN heterostrucure have been investigated with atomic force microscopy, x-ray photoelectron spectroscopy, and TEM. It is revealed that the MBD-grown 16 nm-thick LLO film is polycrystalline with a thin (∼2 nm) amorphous transition layer at the LLO/GaN interface. The bandgap of LLO is derived as 5.3 ± 0.04 eV from O1s energy loss spectrum. Capacitance-voltage (C-V) characteristics of a Ni-Au/LLO/III-nitride metal-insulator-semiconductor diode exhibit small frequency dispersion (&amp;lt;2%) and reveal a high effective dielectric constant of ∼28 for the LLO film. The LLO layer is shown to be effective in suppressing the reverse and forward leakage current in the MIS diode. In particular, the MIS diode forward current is reduced by 7 orders of magnitude at a forward bias of 1 V compared to a conventional Ni-Au/III-nitride Schottky diode.

Threshold Voltage Instability in Al2O3/GaN/AlGaN/GaN Metal–Insulator–Semiconductor High-Electron Mobility Transistors

The threshold voltage (Vth) instability in GaN-based metal–insulator–semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current–voltage (I–V), high-frequency capacitance–voltage (C–V) (HFCV), and quasi-static C–V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (<10 mV) in double-mode (up and down sweep) HFCV characteristics as the maximum forward bias (VFmax) during the sweep is set to 0 V, while an apparent ΔVth (as large as 0.9 V) emerges as VFmax is increased to +5 V for the MIS diode. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques.

Electrical properties of thermally oxidized AlInN/AlN/GaN-based metal oxide semiconductor hetero field effect transistors

In this work, we report on the thermal oxidation of AlInN/AlN/GaN heterostructures. A “nearly native” Al2O3 oxide was formed during this oxidation procedure, which can be used as a gate oxide and thus enables the fabrication of metal insulator semiconductor hetero field effect transistors. A constant barrier height of ΦB ≈ 2.34 eV was obtained for all oxidized samples, independent of the oxidation time and temperature, indicating a stable AlInN-oxide interface. The interface state density was approximated to be as low as Nint = 2.5 × 1012 cm-2. Oxide thicknesses were estimated to be in the range of 0.6 nm and 3.2 nm, resulting in a suppression of reverse leakage currents oflarge area metal insulator semiconductor diodes by up to three orders of magnitude. Two-dimensional electron gas density and, in particular, carrier mobility are strongly affected by the thermal oxidation in the O2 atmosphere. A narrow processing window for successful thermal oxidation was identified, covering temperatures between 700 °C and 800 °C and durations of few minutes. The resulting oxide thickness scales well with the square root of oxidation time, indicating diffusion of oxygen atoms into the barrier.

Hydrogen interaction with GaN metal–insulator–semiconductor diodes

Interaction mechanism of hydrogen with GaN metal–insulator–semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO2 dielectric, the current–voltage (I–V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler–Nordheim tunneling to Poole–Frenkel emission. In sharp contrast, Pt-SixNy-GaN diodes exhibit Poole–Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance–voltage (C–V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.

High-temperature ultraviolet detection based on InGaN Schottky photodiodes

A thermally stable metal-insulator-semiconductor (MIS) Schottky-type photodiode with high performance based on the InGaN film is demonstrated at high temperatures up to 523 K. The reverse leakage current remains at a low level (10−7−10−8 A), while the UV responsivity is as high as 5.6 A/W at −3 V under 523 K, without observing the persistent photoconductivity. The discrimination ratio between ultraviolet (378 nm) and visible light (600 nm) is maintained to be more than 105. The temperature-dependent current-voltage characteristics of the MIS diode were analyzed. The photocurrent gain at reverse biases was interpreted in term of thermionic-field emission (TFE) and field-emission tunneling mechanism from room-temperature to 463 K, while TFE becomes the dominant mechanism at high temperatures.

Matrix-assisted pulsed-laser evaporated polymer films in all-organic field-effect transistors and metal–insulator–semiconductor diodes

The electrical properties of matrix-assisted pulsed-laser evaporated (MAPLE) 9,9-dioctylfluorene-co-bis-N-N-(4-butylphenyl)-bis-N,N-phenyl 1,4-phenylenediamine (PFB)-based bottom-gate organic field-effect transistors (FETs) and metal–insulator–semiconductor (MIS) diodes with poly (methyl methacrylate) (PMMA) as the dielectric layer have been investigated. The device characteristics were found to improve with an increase in the difference between the solubility parameters of PMMA and solvent. Shifts in flat band voltage of the MIS diodes were found to be due to the difference in the density of trapped holes located at the semiconductor–insulator interface. The threshold voltage of the FETs were correlated with differences in acceptor doping density and flat band voltage shifts of the MIS diodes, thereby demonstrating the role of interface traps in determining the electrical properties of organic devices. Electrical characterization of the FET shows the device to have a hysteresis-free operation in its transfer characteristics, a low threshold voltage of −0.2 V, and a field-effect mobility of 0.2 × 10 −4 cm 2 V −1 s −1. Interface trap states of the MIS diodes were found to be distributed in energy with their density decreasing non-linearly from approximately 2.8 × 10 12 to 1.2 × 10 12 eV −1 cm −2 over an energy range of 0.075–0.385 eV above the bulk Fermi level. Non-orthogonality of the semiconductor solvent had no deleterious effects on the underlying PMMA dielectric layer even without any high temperature baking, thus demonstrating that MAPLE is a viable technique for fabricating polymer dielectric-based devices and for improving the semiconductor–insulator interface.

Electrical characterization of Au/n-GaN metal–semiconductor and Au/SiO 2/n-GaN metal–insulator–semiconductor structures

In the present work, we have investigated the current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of Au/SiO 2/n-GaN metal–insulator–semiconductor (MIS) Schottky diode and compared with Au/n-GaN metal–semiconductor (MS) Schottky diode. Calculations showed that the Schottky barrier height and ideality factor of the MS Schottky diode is 0.79 eV ( I– V), 0.87 eV ( C– V) and 1.45, respectively. It is observed that the Schottky barrier height increases to 0.86 eV ( I– V), 0.99 eV ( C– V) and ideality factor deceases to 1.3 for MIS diode. For the MS diode, the calculated doping concentration is 4.17 × 10 17 cm −3. However, in the case of the MIS Schottky diode, the decrease in doping concentration is observed and the respective value is 2.08 × 10 17 cm −3. The obtained carrier concentration of the MIS diode is reduced about 50% when compared to the MS diode. The interface state density as determined by Terman's method is found to be 3.79 × 10 12 and 3.41 × 10 10 cm −2 eV −1 for the MS and MIS Schottky diodes, respectively. The calculated interface densities are 2.47 × 10 11 cm −2 eV −1, 3.35 × 10 11 cm −2 eV −1 and 3.5 × 10 11 cm −2 eV −1 for the sweep rates of 300, 450 and 600 mV/s from MOS C– V measurements for the MIS Schottky diode. The interface state density calculated from Terman's method is found to be increased with sweep rate. From the C– V measurement, it is noted that the decrease in the carrier concentration in MIS diodes as compared to MS diode may be due to the presence of oxide interfacial layer. DLTS measurements have also been performed on MIS Schottky diode and discussed.

Hydrogen sensing performances of Pt/i-ZnO/GaN metal–insulator–semiconductor diodes

Abstracts In light of the same wurtzite structure and the similar lattice constant and band gap energy between ZnO and GaN-based semiconductors, a high quality intrinsic ZnO film is used as the insulating layer for the Pt/i-ZnO/GaN metal–insulator–semiconductor (MIS) hydrogen gas sensors. When the MIS hydrogen gas sensors are exposed to dilute hydrogen ambience, hydrogen dipoles are formed at the Pt/i-ZnO interface with electrons released back to the ZnO. The hydrogen adsorbed reaction leads to the reduction of the barrier height and the series resistance. When the Pt/i-ZnO(10 nm)/GaN hydrogen gas sensors are exposed to 10,000 ppm H 2 at a room temperature, the resultant barrier height change is 211.9 meV and the series resistance is reduced from 21.4 kΩ to 13.4 kΩ. When the operation temperature increases to 500 K, the corresponding barrier height change is 124.5 meV while the series resistance reduces from 2.5 kΩ to 2.3 kΩ. The hydrogen absorption enthalpy at the interface is about −11.8 kJ/mol, which is the characteristic of exothermic reaction.

Electrical and Optical Properties of Diketopyrrolopyrrole-Based Copolymer Interfaces in Thin Film Devices

Two donor-acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) have been synthesized for their application in organic devices such as metal-insulator semiconductor (MIS) diodes and field-effect transistors (FETs). The semiconductor-dielectric interface was characterized by capacitance-voltage and conductance-voltage methods. These measurements yield an interface trap density of 4.2 × 10(12) eV⁻¹ cm⁻² in TDPP-BBT and 3.5 × 10¹² eV⁻¹ cm⁻² in PDPP-BBT at the flat-band voltage. The FETs based on these spincoated DPP copolymers display p-channel behavior with hole mobilities of the order 10⁻³ cm²/(Vs). Light scattering studies from PDPP-BBT FETs show almost no change in the Raman spectrum after the devices are allowed to operate at a gate voltage, indicating that the FETs suffer minimal damage due to the metal-polymer contact or the application of an electric field. As a comparison Raman intensity profile from the channel-Au contact layer in pentacene FETs are presented, which show a distinct change before and after biasing.

Electrical behavior of MIS devices based on Si nanoclusters embedded in SiO x N y and SiO2 films

We examined and compared the electrical properties of silica (SiO2) and silicon oxynitride (SiOxNy) layers embedding silicon nanoclusters (Sinc) integrated in metal-insulator-semiconductor (MIS) devices. The technique used for the deposition of such layers is the reactive magnetron sputtering of a pure SiO2 target under a mixture of hydrogen/argon plasma in which nitrogen is incorporated in the case of SiOxNy layer. Al/SiOxNy-Sinc/p-Si and Al/SiO2-Sinc/p-Si devices were fabricated and electrically characterized. Results showed a high rectification ratio (>104) for the SiOxNy-based device and a resistive behavior when nitrogen was not incorporating (SiO2-based device). For rectifier devices, the ideality factor depends on the SiOxNy layer thickness. The conduction mechanisms of both MIS diode structures were studied by analyzing thermal and bias dependences of the carriers transport in relation with the nitrogen content.