Interface State Density Values Research Articles

The interface state density characterization by temperature-dependent capacitance–conductance–frequency measurements in Au/Ni/n-GaN structures

We have fabricated the Au/Ni/n-GaN structures and measured their capacitance–frequency (C–f) and conductance (G/w)-angular frequency (w) characteristics in the temperature range of 60–320 K. The C–f curves for different reverse bias voltages have shown a behavior almost independent of the bias voltage at frequencies above 300 kHz at each measurement temperature. We have calculated the temperature-dependent interface state density, Nss, values from the G/w versus w curves. The Nss value for the Ni/n-GaN interface ranges from 3.36 × 1011 cm−2 eV−1 at 0.0 V to 2.92 × 1011 cm−2 eV−1 at 0.40 V for 60 K, and 6.63 × 1011 cm−2 eV−1 at 0.0 V to 3.87 × 1011 cm−2 eV−1 at 0.40 V for 320 K. That is, the interface state density value increases with increasing temperature. It has been seen that the values of Nss obtained from the G/w versus w curves of the device are lower than the given values for metal/n-type GaN interface in the literature.

Improved Evaluation Method for Channel Mobility in SiC Trench MOSFETs

We proposed an improved method for evaluating the effective channel mobility (μeff), involving an appropriate definition of the threshold voltage (Vth) based on the ideal gate bias voltage – drain current (VG-ID) characteristics. Using this method, the dependence of μeff on the effective field (Eeff) could be evaluated even for SiC trench MOSFETs with large interface state density (Dit) values. The dominant influence on μeff in the low Eeff region was found to be Coulomb scattering caused by interface states at the SiC/SiO2 interfaces.

Effect of thin gold interlayer on the electrical and dielectrical behaviors of ITO/MEH-PPV/Al structures

The effects of inserting a thin gold (Au) layer between the indium tin oxide (ITO) electrode and the poly [2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene] (MEH-PPV) organic material on the electrical and interface state properties of a ITO/MEH-PPV/Al device are investigated through current–voltage I(V), and capacitance–voltage characteristics C(V). The modified anode was characterized by atomic force microscope (AFM), and UV–vis transmittance spectra. The atomic force microscopy (AFM) surface roughness analysis indicates that a uniform and smoother surface is formed when the ITO is covered by the Au interlayer. A decrease in the transmittance and the optical band gap is observed in ITO/Au anode. The ITO/Au/MEH-PPV/Al device shows improved current density–voltage characteristics as compared with the ITO/MEH-PPV/Al. Diode parameters such as ideality factor, barrier height, series resistance and Shunt resistance are calculated using Schottky model corrected from the series and Shunt resistances. In the presence of the Au interlayer, the junction resistance across the ITO/MEH-PPV interface is significantly reduced, leading to an improvement in hole injection.The interface state density (Nss) values and the time constant of the interface states (τ) are obtained by the development of a new approach by the fit of the capacitance with three capacitances in series, according to Nicollian and Goetzberger formula. A decrease in the interface state density is observed when the Au interlayer is introduced at the ITO/organic layer interface. The main factors contributing to such improvements induced by the thin gold buffer layer are discussed.

Electrical Characteristics of Al/Poly(methyl methacrylate)/p-Si Schottky Device

Al/Poly(methyl methacrylate)(PMMA)/p-Si organic Schottky devices were fabricated on a p-Si semiconductor wafer by spin coating of PMMA solution. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of Al/PMMA/p-Si structures have been investigated in the frequency range of 1 kHz–10 MHz at room temperature. The diode parameters such as ideality factor, series resistance and barrier height were calculated from the forward bias current–voltage (I–V) characteristics. In order to explain the electrical characteristics of metal–polymer–semiconductor (MPS) with a PMMA interface, the investigation of interface states density and series resistance from C–V and G–V characteristics in the MPS structures with thin interfacial insulator layer have been reported. The measurements of capacitance (C) and conductance (G) were found to be strongly dependent on bias voltage and frequency for Al/PMMA/p-Si structures. The values of interface state density (Dit) were calculated. These values of Dit and series resistance (Rs) were responsible for the non-ideal behavior of I–V and C–V characteristics.

Electrical Conduction Mechanisms in n-CdS/p-CuFeO<sub>2</sub> Heterojunction Diode

In this work, n-CdS/p-CuFeO2 heterojunction diode was fabricated by thermal evaporating CdS thin films on 1 mm thick-CuFeO2 ceramic substrate with substrate temperature kept at 373 K during evaporation process. The forward current-voltage characteristics of n-CdS/p-CuFeO2 heterojunction in a temperature range of 100-300 K were investigated to determine the electrical parameters and conduction mechanism. It was found that, at forward bias below 0.5 V, the conduction mechanism of the diode is dominated by thermionic emission (TE) mechanism. At bias voltage above 0.5 V, the current transport is due to space charge limited current (SCLC) controlled by an exponential trap distribution in the band gap of CdS. The temperature dependence of the saturation current and ideality factor are well described by tunneling enhanced recombination at junction interface with activation and characteristic tunneling energy values as about 1.79 eV and E00 = 86 meV, respectively. The value of interface state density (Nss) evaluated from capacitance spectroscopy increases from 2.09x1011 eV-1cm-2 (at 300 K) to 2.70x1011 eV-1cm-2 (at 363 K). Free carrier concentration of 5.80x1013 cm-3 at room temperature was estimated from capacitance-voltage measurements at 50 kHz.

Electrical Characterization of Atomic Layer Deposited La2O3 Films on In0.53Ga0.47As Substrates

The effect of La2O3 atomic-layer-deposition (ALD) conditions by La(iPrCp)3 and H2O, on the electrical properties of metal/La2O3/In0.53Ga0.47As MOS capacitor has been investigated. We found that the low growth temperature can effectively improve the La2O3/In0.53Ga0.47As interface properties and gate leakage current. It is shown that by controlling the growth temperature of ALD, near ideal capacitance-voltage (C-V) characteristics with low interface state density (Dit) values (~8 x 1011 eV-1cm-2) can be obtained.

Capacitance-voltage characterization of interfaces between positive valence band offset dielectrics and wide bandgap semiconductors

A photo-assisted capacitance voltage (C-V) characterization technique for interfaces between positive valence band offset dielectrics (Al2O3, SiO2) and wide bandgap semiconductors is presented. It is shown that the valence band barrier for holes at the interface affects the measurement and a method to extract border trap and interface state density values from the measured C-V curves is suggested. Dielectric-semiconductor interface characterization has been well studied for silicon but the characterization techniques are not transferable to wide bandgap semiconductors, such as GaN and SiC, due to the low minority carrier generation rate. Multiple dielectrics deposited by various techniques have been employed in these devices; but in order to ascertain the most suitable dielectric, an effective characterization technique that works well with dielectrics on wide-bandgap semiconductors is required.

Charge-controlled fixation of DNA molecules on silicon surface and electro-physical properties of Au–DNA–Si interface

Light-induced fixation of DNA molecules on silicon surface was done and electro-physical properties of Schottky diodes with DNA on interfaces were investigated. Thymus DNA molecules were deposited on silicon from a water solution. Fixed molecular structures were observed with helium ionic microscopy and atomic force microscopy and then they were covered with thermal sputtered gold film. Obtained structures Au–DNA–(n-Si) were examined with current–voltage and frequency dependent admittance measurements. In darkness immobilizing of molecules leaded to form DNA ropes with thickness up to 10nm and distances between them about 1mkm. Fixation under illumination resulted in forming of single DNA mesh with thickness about 1nm and cell size about 100nm. Presence of molecular mesh on interface leaded to increasing of charge density controlled by metal Fermi level and improved diode quality. Presence of molecular ropes resulted in increasing of charge density controlled by semiconductor. From the estimation of interface state density values the origin of the states at the interface between DNA and silicon substrate is suggested to be DNA phosphate groups contacting or being close to the substrate surface.

Interface states at the SiN/AlGaN interface on GaN heterojunctions for Ga and N-polar material

Dielectric passivation is important to improve the stability and reliability of gallium nitride based semiconductor devices. We need to characterize various dielectrics and their interfaces to nitrides accurately to be able to exploit the benefits efficiently. Earlier, B. L. Swenson and U. K. Mishra [J. Appl. Phys. 106, 064902 (2009)] have detailed a photo-assisted high frequency CV characterization technique for the Ga-polar SiN/GaN interface that gives an accurate value of interface state density (Dit) across the bandgap of the dielectric. In this work, we extend the technique to study the interface states at the SiN/AlGaN interface on GaN for Ga and N polar material. This simulates the AlGaN/GaN HEMT structure. A MIS-type structure comprised of a metal on SiN on an AlGaN/GaN heterojunction was used for the study. For a structure with 1 nm AlGaN interlayer, a peak interface state density of 2.8 × 1012 cm−2 eV−1 was measured. For Ga polar devices, the measured Dit decreases with increasing AlGaN thickness. In the N-polar case, the measured Dit increases with increasing AlGaN thickness. The variations of measured Dit with AlGaN thickness, in both cases, can be explained by screening from the accumulation charge at the AlGaN/GaN interface.

Admittance Spectroscopy of Interface States in $ \hbox{ZnO/HfO}_{2}$ Thin-Film Electronics

The electronic properties of ZnO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface states are studied by dc current-voltage and ac admittance spectroscopy on thin-fllm transistors (TFTs) and metal-insulator-semiconductor capacitor structures. Subthreshold behavior of the transistors indicates an interface state density (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) value of 7.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . Cole-Cole plots of ac admittance demonstrate Debye behavior and extracted energy-dependent inter face state density (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) with an approximate exponential decay of 3.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> · eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> near the conduction band to 1.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> · eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 0.9 eV below the conduction band. The integrated interface state density from these measurements is N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> = 7.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , which is consistent with the value obtained from subthreshold behavior of the TFTs.

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.

Effect of the frequency and temperature on the complex impedance spectroscopy (C–V and G–V) of p-ZnGa2Se4/n-Si nanostructure heterojunction diode

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa2Se4/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain e were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa2Se4/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (C–V), conductance–voltage (G–V), and series resistance–voltage (Rs–V) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential Vbi, the doping concentration Nd and the barrier height φb(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.

Interface state densities, low frequency noise and electron mobility in surface channel In 0.53Ga 0.47As n-MOSFETs with a ZrO 2 gate dielectric

This paper reports on an investigation of interface state densities, low frequency noise and electron mobility in surface channel In 0.53Ga 0.47As n-MOSFETs with a ZrO 2 gate dielectric. Interface state density values of D it ∼ 5 × 10 12 cm −2 eV −1 were extracted using sub-threshold slope analysis and charge pumping technique. The same order of magnitude of trap density was found from low frequency noise measurements. A peak effective electron mobility of 1200 cm 2/Vs has been achieved. For these surface channel In 0.53Ga 0.47As n-MOSFETs, it was found that η parameter, an empirical parameter used to calculate the effective electric field, was ∼0.55, and is to be comparable to the standard value found in Si device.

Electrical characterization and fabrication of organic/inorganic semiconductor heterojunctions

Thin films of polyaniline (PANI) titanium dioxide (TiO2) nanocomposites prepared with and without surfactant (tetradecyltrimethylammonium bromide, TTAB) were formed by spin coating onto chemically cleaned p-type silicon substrates. The current–voltage characteristics of the Au/PANITiO2/p-Si/Al and Au/PANITiO2TTAB/p-Si/Al heterojunctions had rectifying behavior with the potential barrier formed between the polymeric thin films and p-Si semiconductor, and they were analyzed on the basis of the standard thermionic emission (TE) theory. Cheung functions combined with conventional forward I–V characteristics were used to obtain diode parameters such as barrier height, ideality factor and series resistance (Rs). The values of barrier height, ideality factor and Rs were found as 0.496±0.003 eV, 2.313±0.067 and 23.633±7.554 Ω for the Au/PANITiO2/p-Si/Al device; 0.494±0.003 eV, 2.167±0.018 and 12.929±2.217 Ω for the Au/PANITiO2TTAB/p-Si/Al device. In addition, the energy distributions of the interface state density of the devices were determined from the forward I–V characteristics by taking into account the bias dependence of the ideality factor and barrier height. It was seen that the PANITiO2TTAB/p-Si device had slightly higher interface state density values than those of the PANITiO2/p-Si device.

Improved Electrical Properties and Thermal Stability of GeON Gate Dielectrics Formed by Plasma Nitridation of Ultrathin Oxides on Ge(100)

We demonstrated the impact of plasma nitridation on thermally grown GeO2 for the purposes of obtaining high-quality germanium oxynitride (GeON) gate dielectrics. Physical characterizations revealed the formation of a nitrogen-rich surface layer on the ultrathin oxide, while keeping an abrupt GeO2/Ge interface without a transition layer. The thermal stability of the GeON layer was significantly improved over that of the pure oxide. We also found that although the GeO2 layer is vulnerable to air exposure, a nitrogen-rich layer suppresses electrical degradation and provides excellent insulating properties. Consequently, we were able to obtain Ge-MOS capacitors with GeON dielectrics of an equivalent oxide thickness (EOT) as small as 1.7 nm. Minimum interface state density (Dit) values of GeON/Ge structures, i.e., as low as 3 x 1011 cm-2eV-1, were successfully obtained for both the lower and upper halves of the bandgap.

Controlling of electrical characteristics of Al/p-Si Schottky diode by tris(8-hydroxyquinolinato) aluminum organic film

We study how tris(8-hydroxyquinolinato) aluminum organic semiconductor layer at p-silicon/Al interface can affect electrical transport across this interface. Al/Alq3/p-Si device shows a good rectifying behavior with an ideality factor value of 1.95. The barrier height values obtained from I– V and Norde method were found to be 0.84 and 0.82 eV, respectively. This indicates that the barrier height obtained from Norde method is lower than that of barrier height value obtained from I– V due to the series resistance effect. The modification of the interfacial potential barrier for Al/p-Si diode was achieved using an interlayer of the Alq3 organic semiconductor and this is ascribed to the fact that the Alq3 interlayer increases the effective barrier height, because of the interface dipole induced by passivation of the organic layer. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance and interface state density values. The series resistance of the diode was changed from 9 kΩ to 1 kΩ with increasing frequency. The distribution profile of R s – V gives a peak at low frequencies in the depletion region and disappears with increasing frequency.

Capacitance and conductance–frequency characteristics of Au–Sb/p-GaSe:Gd Schottky barrier diode

The Schottky barrier height (SBH) values have been obtained from the reverse bias capacitance–voltage ( C– V) characteristics of Au–Sb/p-GaSe:Gd Schottky barrier diode (SBD) in the temperature range of 180–320 K. The forward bias capacitance–frequency ( C– f) and conductance–frequency ( G– f) measurements of Au–Sb/p-GaSe:Gd SBD have been carried out from 0 to 1.00 V with steps of 0.05 V, whereby the energy distribution of the interface states and their relaxation time have been determined from these characteristics. It has been seen that there is a good agreement between the experimental and theoretical C– f and G– f values. Also, the capacitance values obtained from C– f measurements have shown almost a plateau up to a certain value of frequency, then, have decreased. It has been seen that the interface state density has a very small density distribution range (6.02 × 10 10–6.80 × 10 10 cm −2 eV −1) in the energy range of (0.21− E v)–(1.21− E v) eV with bias from the midgap towards the top of the valence band. The interface state density values calculated for Au–Sb/p-GaSe:Gd SBD are rather low than those given in the literature.

Electrical characterization of nanocluster n-CdO/p-Si heterojunction diode

The nanocluster n-CdO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and optical properties of the nanocluster CdO film have been investigated. The CdO film has a polycrystalline with a cubic monteponite phase. The scanning electron microscopy images indicate that the surface morphology CdO film is almost homogeneous and the CdO film is consisted of the clusters formed with coming together of the nanoparticles. The optical band gap of the CdO film was found to be 2.45 eV using optical absorption method. The electrical properties of the p–n heterojunction composed of transparent CdO and p-Si semiconductors were investigated by current–voltage and conductance–frequency methods. The ideality factor of the diode was found to be 5.41 and the obtained n value is higher than unity due to the interface states between the two semiconductor materials and series resistance. The reverse current of the diode strongly increases with illumination intensity of 100 mW cm −2 and the diode gives a maximum open circuit voltage V oc of 0.12 V and short-circuits current I sc of 0.53 × 10 −6 A. The interface state density values for the diode were found to vary from 7.82 × 10 13 to 3.02 × 10 12 eV −1 cm −2 under various bias voltages.

Electrical characterization of the boron trifluoride doped poly(3‐aminoacetophenone)/p‐Si junction

AbstractElectrical and interface state properties of the borontrifluoride doped poly(3‐aminoacetophenone)/p‐Si junction have been investigated by current‐voltage and impedance spectroscopy methods. Al/p‐Si/P3APBF3/Aldiode indicates a nonideal behavior with electrical parameters (n = 3.53, ϕB = 0.82 eV, and Rs = 1.48 kΩ), which result from the interfacial layer, series resistance, and resistance of the organic semiconductor. The obtained barrier height value of the Al/p‐Si/P3APBF3/Aldiode is higher than that of the conventional Al/p‐Si (ϕB = 0.58 eV) Schottky diode. The interface state density of the diode was of the order of 1.05× 1012 eV−1 cm−2. It is evaluated that the barrier height and interface state density values of the diode are modified using the boron trifluoride doped poly (3‐aminoacetophenone) organic semiconductor. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Germanium oxynitride gate dielectrics formed by plasma nitridation of ultrathin thermal oxides on Ge(100)

Germanium oxynitride (GeON) gate dielectrics with surface nitrogen-rich layers were fabricated by plasma nitridation of thermally grown oxides (GeO2) on Ge(100). Insulating features of ultrathin GeO2 layers of around 2-nm-thick were found to improve with plasma treatment, in which leakage current was drastically reduced to over four orders of magnitude. Consequently, Au/GeON/Ge capacitors of an equivalent oxide thickness down to 1.7 nm were achieved while keeping sufficient leakage reduction merit. The minimum interface state density values of GeON/Ge structures as low as 3×1011 cm−2 eV−1 were obtained for both the lower and upper halves of the bandgap without any postnitridation treatments. These results were discussed based on the effects of plasma nitridation on a degraded GeO2 surface for recovering its electrical properties by creating stable nitride layers.