Energy Distribution Of Interface States Research Articles

The Hydrogenation Impact on Electronic Properties of p-Diamond/n-Si Heterojunctions.

The undoped polycrystalline diamond films (PDFs) have been deposited on n-type silicon (Si) by Hot Filament Chemical Vapor Deposition (HF CVD) technique. The reaction gases are a mixture of methane and hydrogen. The obtained PDFs were characterized by scanning electron microscopy (SEM) and Raman spectroscopy which, in addition to the diamond phase, also confirms the presence of sp hybridized carbon bonds. As-grown CVD diamond layers are hydrogen terminated and show p-type conductivity. The effect of the level of hydrogenation on the electrical properties of p-diamond/n-Si heterojunctions has been investigated by temperature dependent current–voltage (J-V/T) characteristics. The obtained results suggest that the energy distribution of interface states at the grain boundary (GB) subjected to hydrogenation becomes shallower, and the hole capture cross-section can be reduced. Hydrogenation can lead to a significant reduction of the GB potential barrier. These results can be interesting from the point of view of hydrogen passivation of GBs in microelectronics.

Temperature dependence of interface state density distribution determined from conductance–frequency measurements in Ni/n-GaP/Al diode

The conductance measurements of the non-annealed (D1) and 400 °C annealed (D2) Ni/n-GaP/Al diodes were made over a wide frequency range of (10 kHz to 5 MHz) and temperature of (100–320 K with steps of 20 K) with bias voltage as a parameter. The capacitance and conductance measurement method is one of the most popular non-destructive methods to obtain information about metal–semiconductor (MS) diode interfaces. The interface state density distribution curves were determined over the band-gap energy near the semiconductor energy midgap. The interface state density (Dit) has been seen to be of the order of ∼1012 eV−1 cm−2. The Dit∼T curves have been plotted for different values of bias voltage. The value of Dit increased with increasing measurement temperature, and with increasing voltage from negative bias to positive bias voltage for both diodes. It was seen that the Dit value for D2 diode was greater than that for the D1 diode at each measurement temperature and bias voltage. It was seen in the interface state energy distribution or density distribution curves that the value of Dit has increased from the valence band maximum (Ev) towards conduction band minimum (Ec) at each measurement temperature.

Energy distribution of interface states generated by oxygen plasma treatment for control of threshold voltage in pentacene thin-film transistors

Pentacene metal-oxide-semiconductor (MOS) capacitors with a SiO2 dielectric treated by oxygen plasma have been studied by capacitance-voltage (C-V) measurements to investigate the energy distribution of the interface states. Oxygen plasma treatment, which is used for control of the threshold voltage in pentacene thin-film transistors, shifted the C-V curves of pentacene MOS capacitors to a positive gate voltage as well as the transfer curves of pentacene thin-film transistors (TFTs). The shift is explained by electrons captured at interface states generated by oxygen plasma treatment. The interface states capturing the electrons are expected to locate at low energy levels. The energy distribution of the interface states locating at middle or high energy levels was extracted by a method equivalent to the Terman method. By use of the method in two steps, the interface state densities distributed at middle and high energy levels (D M and D H) were separately obtained. D M and D H were of the order of 1010–1012 cm−2 eV−1, and increased with an increase in plasma treatment time.

Direct Observation of Energy Distribution of Interface States at SiO2/4H-SiC Interface

For the interface states at the SiO2/SiC interface, the energy distribution of interface states in the whole-gap region of SiC cannot be obtained from electrical method such as capacitance-voltage and conductance-voltage methods because deep interface states cannot respond to the electrical signal due to their extremely large time constants. Thus interface states at the SiO2/SiC interface in the SiC whole-gap region have not been obtained even though the observation of the energy distribution of interface states is indispensable for further improvement of the electrical properties. We have recently developed a spectroscopic method to observe the energy distribution of interface states based on photoelectron spectroscopic measurements under bias voltage (PES-BA) [1,2]. In the present study, we have investigated the energy distribution of interface states at the SiO2/4H-SiC interface using PES-BA. A Pt(10nm)/SiO2(8nm)/4H-SiC(0001) was used in the present study. The PES-BA measurements were performed using BL15XU at SPring-8. For PES-BA measurements, the incident photon energy was 5.95 keV, while the total energy resolution was set to 240 meV. Applying a positive bias voltage of 2.0V to SiC with respect to the Pt overlayer shifted the Si 1s substrate peak toward a higher binding energy by 0.61 eV. On the other hand, applying a -2.4 V voltage shifted the Si 1s peak toward a lower binding energy by 0.68 eV. These bias-induced shifts were completely reversible; that is, the shift diminished upon removing the bias voltage. Therefore, these shifts were not due to a bias-induced chemical reaction, but were caused by the accumulation or release of charge in the electronic states by the bias. Thus, by analyzing the these shifts as a function of bias voltage, we obtained the energy distribution of the interface states for the SiO2/4H-SiC(0001) interface. Note that the principle for the determination of interface states was described in our previous papers [1-3] For the observed interface states, uniform interface states in the whole gap existed while high density interface states were present near the CBM. By referencing previous theoretical calculations, the observed interface states were assigned. The sharp interface states observed below CBM may be attributed to Si2-C-O states at the interface. For the uniform interface states, two dimensional graphitic carbon and/or chemical disorder may be responsible for the uniform interface states because of the spectrum shape. The synchrotron measurements were performed under the approval of NIMS Beamline Station (Proposal No. 2013B4600 and No. 2014B4602). This study is collaboration with Prof. R. Hasunuma at Tsukuba University

Direct Observation of Energy Distribution of Interface States at SiO2/4H-SiC Interface

The energy distribution of the interface states at the SiO2/4H-SiC(0001) interface was obtained using operando photoelectron spectroscopy. For the interface states, sharp and high density interface states were observed near the conduction band minimum and uniform interface states were present in the entire SiC band-gap. The uniform interface states observed in the whole gap were attributed to graphitic carbon clusters at the interface although the sharp interface states could not be assigned currently.

Accuracy of the Energy Distribution of the Interface States at the SiO2/SiC Interface by Conductance Method

The electrical characteristics of the SiC metal-oxide-semiconductor field effect transistor (MOSFET) have been limited by large amount of states at the SiO2/SiC interface. In this study, the accuracy of the energy level of the interface states extracted by hypothetical high frequency extreme, which is conventionally used, is experimentally examined. Conductance measurements at low temperature between 65 K and 100 K reveal that the extracted energy distribution of the interface states at nitrided SiO2/SiC interface close to the conduction band edge depends on the measurement temperature. It is demonstrated that conductance method at 65K enables us more accurate evaluation of the interface states at the SiO2/SiC interface and found that the interface states density (Dit) of nitride SiO2/SiC interface is over 1013 cm-2eV-1 at energy level of 0.1 eV below the conduction band edge.

The Effect of Interface States Density Distribution and Series Resistance on Electrical Behaviour of Schottky Diode

The forward and reverse bias current-voltage characteristics of the In/p-Si Schottky barrier diode (SBD) have been investigated in the temperature range of 360K to 120K. The current-voltage measurements have been used to extract the electrical parameters such as series resistance, barrier height, ideality factor and interface states density distribution. The higher values of series resistance, ideality factor and interface states energy distribution at low temperature was attributed to the presence of an interfacial insulated layer, popularly known as metal-insulator-semiconductor (MIS) devices. The temperature dependence energy distribution profile of interface states was obtained from the forward bias I-V-T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density (NSS) decreased with increasing temperature was explained by the result of atomic restructuring and reordering at the metal semiconductor interface.

硬 X 線光電子分光による酸化膜の評価

We report the applications of a hard X-ray photoelectron spectroscopy to the characterization of SiO2/Si(001) systems. Large escape depth of high-energy photoelectron enables us to probe buried layers and their interfaces in multilayer structures. Estimation of SiO2 overlayer thicknesses up to 25 nm by angle resolved XPS was possible in SiO2/Si(001) samples. Determination of the thickness profile of a wedged shape SiO2 buried layer was successfully done in Ir (8 nm)/HfO2 (2.2 nm)/thickness graded-SiO2 (0-10 nm)/Si(100). The Si 1s core level showed a SiO2 thickness dependent shift, which was ascribed to fixed charge at the SiO2-Si interface. Energy distribution of interface states at ultrathin thermal oxide/Si(100) interfaces were determined by Si 1s core level shift by applying gate bias in metal-oxide-semiconductor (MOS) structure with 5 nm Au gate electrodes.

Density and energy distribution of interface states in the grain boundaries of polysilicon nanowire.

Wafer-scale fabrication of semiconductor nanowire devices is readily facilitated by lithography-based top-down fabrication of polysilicon nanowire (P-SiNW) arrays. However, free carrier trapping at the grain boundaries of polycrystalline materials drastically changes their properties. We present here transport measurements of P-SiNW array devices coupled with Kelvin probe force microscopy at different applied biases. By fitting the measured P-SiNW surface potential using electrostatic simulations, we extract the longitudinal dopant distribution along the nanowires as well as the density of grain boundaries interface states and their energy distribution within the band gap.

Direct measurement of donor-like interface state density and energy distribution at insulator/AlGaN interface in metal/Al2O3/AlGaN/GaN by photocapacitance method

We determined the energy distribution of donor-like interface state density DitD(E) at the Al2O3/AlGaN interface in a metal/Al2O3/AlGaN/GaN heterostructure (MISH) capacitor. In this order, we developed a point-by-point graphical method based on the measurement and simulations of the MISH photocapacitance versus ultraviolet light intensity. We found a tail-like shaped DitD(E) strongly decreasing from the value of 5×1013 to 4×1012 eV−1 cm−2 in the energy range between 0.12 eV and 0.45 eV from the AlGaN valence band edge.

Effect of annealing temperature on the electrical properties of Au/Ta2O5/n-GaN metal–insulator–semiconductor (MIS) structure

We report on the effect of an annealing temperature on the electrical properties of Au/Ta2O5/n-GaN metal–insulator–semiconductor (MIS) structure by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The measured Schottky barrier height (Φbo) and ideality factor n values of the as-deposited Au/Ta2O5/n-GaN MIS structure are 0.93 eV (I–V) and 1.19. The barrier height (BH) increases to 1.03 eV and ideality factor decreases to 1.13 upon annealing at 500 ∘C for 1 min under nitrogen ambient. When the contact is annealed at 600 ∘C, the barrier height decreases and the ideality factor increases to 0.99 eV and 1.15. The barrier heights obtained from the C–V measurements are higher than those obtained from I–V measurements, and this indicates the existence of spatial inhomogeneity at the interface. Cheung’s functions are also used to calculate the barrier height (Φbo), ideality factor (n), and series resistance (Rs) of the Au/Ta2O5/n-GaN MIS structure. Investigations reveal that the Schottky emission is the dominant mechanism and the Poole–Frenkel emission occurs only in the high voltage region. The energy distribution of interface states is determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height. It is observed that the density value of interface states for the annealed samples with interfacial layer is lower than that of the density value of interface states of the as-deposited sample.

Interface trap characterization of atomic layer deposition Al2O3/GaN metal-insulator-semiconductor capacitors using optically and thermally based deep level spectroscopies

Quantitative measurements of interface state density and energy distribution profiles within Al2O3/GaN interfaces were obtained by constant capacitance deep level transient spectroscopy and deep level optical spectroscopy (CC-DLTS/DLOS). The new application of CC-DLOS to interface state measurement is described, which allows interrogation of very deep interface states. A series of Al2O3/GaN metal-insulator-semiconductor (MIS) devices prepared as a function of Al2O3 thickness via atomic layer deposition, on NH3-MBE-grown n-type Ga-polar GaN layers enabled a systematic study. The overall shape and magnitude of the interface trap distribution, Dit, were determined to be nearly identical, independent of Al2O3 thickness. The Al2O3/GaN Dit spectra had an overall U-shape with Dit ∼1012 cm−2 eV−1 near the conduction band edge, ∼1011 cm−2 eV−1 mid-gap, and ∼1014 cm−2 eV−1 near the valence band edge. However, the interface states near the GaN conduction band showed a slight inverse dependence on Al2O3 thickness, suggestive of annealing effect during deposition. The high near valence band state concentrations are consistent with expectations from residual carbon impurities at the GaN surface. A method for discriminating between bulk and interface states in the CC-DLTS signal is demonstrated, using the results on MIS capacitors in combination with spectroscopy results on a Schottky diode structure.

Successive ion layer adsorption and reaction (SILAR) technique synthesis of Al(III)–8-hydroxy-5-nitrosoquinolate nano-sized thin films: Characterization and factors optimization

Nano Al(III)–8-hydroxy-5-nitrosoquinolate [Al(III)–(HNOQ)3] thin films were synthesized by the rapid, direct, simple and efficient successive ion layer adsorption and reaction (SILAR) technique. Thin film formation optimized factors were evaluated. Stoichiometry and structure were confirmed by elemental analysis and FT-IR. The particle size (27–71nm) was determined using scanning electron microscope (SEM). Thermal stability and thermal parameters were determined by thermal gravimetric analysis (TGA). Optical properties were investigated using spectrophotometric measurements of transmittance and reflectance at normal incidence. Refractive index, n, and absorption index, k, were determined. Spectral behavior of the absorption coefficient in the intrinsic absorption region revealed a direct allowed transition with 2.45eV band gap. The current–voltage (I–V) characteristics of [Al(III)–(HNOQ)3]/p–Si heterojunction was measured at room temperature. The forward and reverse I–V characteristics were analyzed. The calculated zero-bias barrier height (Φb) and ideality factor (n) showed strong bias dependence. Energy distribution of interface states (Nss) was obtained.

Analysis of the series resistance and interface states of Au/Si3N4/n-Si (metal–insulator–semiconductor) Schottky diodes using I–V characteristics in a wide temperature range

In this work, we investigated the current–voltage (I–V) characteristics of an Au/Si3N4/n-Si (metal–insulator–semiconductor (MIS)) Schottky diode in a wide temperature range of 160–400 K. By using the thermionic emission (TE) theory, the forward bias I–V characteristics were analyzed to estimate the MIS Schottky diode parameters. Experimental results show that the main electrical parameters, such as the ideality factor (n) and the zero-bias barrier height (ΦB0), are considerably dependent on temperature. The semi-logarithmic ln I–V characteristics based on the TE mechanism showed a decrease in n and an increase in ΦB0 with increasing temperature. The values of n and ΦB0 changed from 9.50 and 0.34 eV (at 160 K) to 3.43 and 0.74 eV (at 400 K), respectively. Therefore, these results cannot be explained purely on the basis of TE theory. The temperature dependence of the energy distribution of interface states (Nss) was obtained from the forward bias I–V measurements by taking into account the bias dependence of the effective barrier height (Φe) and n. In addition, the values of series resistance (Rs) were determined using Cheung's method and Ohm's law.

Strong reduction in the density of interface states at the SiO2/4H-SiC interface after oxidation in the presence of alkali ions

We report a strong reduction in the density of near-interface traps at the SiO2/4H-SiC interface after dry oxidation in the presence of potassium. This is accompanied by a significant enhancement of the oxidation rate. The results are in line with recent investigations of the effect of sodium on oxidation of 4H-SiC. It is evident that the presence of such alkali metals enhances the oxidation rate of SiC and strongly influences the energy distribution of interface states.

Measuring the concentration and energy distribution of interface states using a non-contact corona oxide semiconductor method

The electronic states distribution at the Si-SiO2 interface was measured by combining contactless corona charge-voltage measurement and low-frequency capacitance voltage method. Using device equivalent circuit modeling, we were able to obtain the silicon-insulator interface states energy distribution across the whole Si band gap with a single measurement. The measured distribution has the well known u-shaped curve, with a minimum around mid gap of 2 × 1010 cm−2 eV−1 and maximum values close to the band edges reaching 6 × 1013 cm−2 eV−1. Two distinct peaks were observed at 0.21 eV and 0.88 eV above the valence band maximum which correspond to the Si (100) Pb0 centers.

On the energy distribution of interface states and their relaxation time profiles in Al/pentacene/p-GaAs heterojunction diode

The energy density distribution profile of the interface states (Nss) and their relaxation time (τ) of Al/pentacene/p-GaAs heterojunction diodes were obtained from the admittance spectroscopy method, which is included in capacitance/conductance-voltage measurements in the frequency range of 10 kHz-1 MHz at room temperature. The values of Nss were also obtained from the forward bias current-voltage measurements by taking into account voltage-dependent barrier height, and the results were compared with those obtained using admittance method. The values of Nss and τ obtained from admittance measurements range from 1.53 × 1011 eV–1 cm–2 and 1.33 µs in (0.596-Ev) eV to 1.90 × 1011 eV–1 cm–2 and 8.18 µs in (0.673-Ev) eV, respectively. In addition, the values of Nss were obtained using Hill-Coleman method as a function of frequency. The values of Nss obtained from these three methods are in the same order and in good agreement with one another. Low values of Nss can be attributed to the interfacial pentacene layer between metal and semiconductor. This magnitude of Nss is very suitable for the fabrication of electronic devices. The C values of these diodes decrease with increasing frequency both in inversion and depletion regions, but give a peak in the accumulation region due to the effect of series resistance. The increase in C, especially at low frequencies, results from the presence of interface states at GaAs/pentacene interface.

Hydrogenation of interface states at a clean grain boundary in the direct silicon bonded wafer

AbstractThe effect of hydrogenation on the electrical property of a clean grain boundary (GB) in the p‐type direct silicon bonded (DSB) wafers has been investigated by current–voltage (I–V) and capacitance–voltage(C–V) deconvolution. It is found that compared to the as‐bonded GB, the energy distribution of interface states at the GB subjected to hydrogenation become shallower, and the hole capture cross‐section can be reduced by about two orders of magnitude, while the density of GB states changes only slightly. Therefore, a significantly smaller potential barrier of GB could be obtained after hydrogenation. These results are interesting for us to understand the mechanism of hydrogen passivation of GBs in photovoltaics.

Effect of post deposition anneal on the characteristics of HfO2/InP metal-oxide-semiconductor capacitors

The interface trap density (Dit) and bonding of the HfO2/InP interface is investigated. The energy distribution of interface states extracted using capacitance-voltage measurements show a peak near midgap in InP and a tail, which extends into the InP conduction band. Both the Dit peak and the conduction band Dit increase with increasing post-deposition annealing temperature. A substantial increase in the native oxides with annealing temperature is observed with x-ray photoelectron spectroscopy. The possible bonding states responsible for the defects are presented.

Reduction in the Density of Interface States at the SiO<sub>2</sub>/4H-SiC Interface after Dry Oxidation in the Presence of Potassium

We report a strong reduction in the density of near-interface traps (NITs) at the SiO2/4H-SiC interface after dry oxidation in the presence of potassium. This is accompanied by a significant enhancement of the oxidation rate. The results are in line with recent investigations of the effect of sodium on oxidation of 4H-SiC. It is evident that both alkali metals enhance the oxidation rate of SiC and strongly influence the energy distribution of interface states.