ICMCTF2012 Session CP: Symposium C Poster Session

For preparation of new material transparent electrode, we prepared the Ga and Al doped ZnO (Ga-Al-ZnO; GAZO) thin film under various conditions by using facing targets sputtering (FTS) system as function of input current and thermal treatment temperature.

The FTS system can prepare the thin film using new materials because it uses two targets. Also, the substrate is located in a plasma-free area apart from the center of plasma so it can suppress high energy particles colliding to the substrate so high quality films can be prepared.

The properties of the as-deposited GAZO thin films were then examined by 4-point prove, atomic force microscope (AFM), X-ray diffractometer (XRD), and field emission scanning electron microscope (FESEM) and UV-VIS spectrometer. As a result, the lowest sheet resistance of the films showed 59.3 ohm/sq and average transmittance about 90% in the visible range. And after thermal treatment, we could observe the more improved properties of GAZO thin film. The lowest sheet resistance (47.3ohm/sq) of the GAZO thin films were shown at thermal treatment temperature of 300˚C. It is considered that this is the result of continuous substitutions by dopants and improved crystalline by thermal treatment.

Sb-Sn oxide (ATO), a good TCO, thin film was reactively sputtered on a glass, and characterized as the Sb contents and annealing temperatures, by transmission, reflection, absorption, resistivity, film thickness, refractive index n and k, XRD, Hall probe and ellipsometer (300~1000nm).

An ellipsometry method was developed to determine the ATO film carrier density and gradience. There are some reports on the resistivity evaluation based on the Drude model through ellipsometer measurements. However, the uniqueness of the model fitting is poor in many conditions, (many values could fit the model, so that no unique value could be precisely determined). In theory: Tauc-Lorentz and Drude could give good description of the band-gap and free carrier physics of the ellipsometry spectra. The reason of poor uniqueness value in model fitting lies in that the measurement data content is not enough to uniquely determine physical parameters; thus the simulation will face uniqueness issue for the solution.

How to increase the measurement data content is a key to improve the uniqueness of the simulation. Multiple angles did not help much on this data content issue. The transmission and reflection spectra measurements were helpful at some cases. However, the uniqueness is still poor in many other cases in our ATO film study. Here we present a new method that combined resistivity measurement into modeling, instead of simulating resistivity ρ. Thus, this method increases measurement data content, so it significantly improved the uniqueness of the solution in the modeling; thus, through Drude model relationship, the carrier density and mobility of the ATO film could be uniquely determined.

Drude model: the dielectric constant ε is function of resistivity ρ, scattering time τ i, and wavelength λ. Then electron density N and mobility μ could be calculated from ρ=m*/(Nq²τ) , if assumed m* is a constant (such as 0.3m_e)

The gradience profile simulation is widely used for ellipsometry simulation, combined with the above method, the gradience of carrier density and mobility can be estimated, in comparison of Hall probe measurements, two methods provides similar carrier density and mobility, but the former one here could provide gradience information.

In this study, a new method was developed to significantly improve the ellipsometry simulation uniqueness, so that the carrier density and mobility of the ATO film could be uniquely determined. The gradience information could be estimated, and presented.

Transparent conductive oxides (TCO) have become crucial not only as contact layers in photovoltaic applications, but also in electrochromic devices, low emissivity glass for commercial buildings, TFT-LCD displays and touch panels, as well as in flexible PV applications. With new applications come new specifications, and the corresponding need to simultaneously optimize materials properties for new parameters. Such parameters could include physical properties such as flexibility, or thermal properties such as emissivity.

With increasing numbers of experiments needed to explore expanding process spaces, more efficient technologies and methodologies are needed to be able to develop new materials. Intermolecular Inc.’s (IM) High Productivity Combinatorial (HPC) Physical Vapor Deposition (PVD) platform is capable of screening up to 4 materials at a time. Co-sputtering of multiples sources (two to four) allows for an exponential numbers of site isolated experiments with unique composition to be deposited and characterized simultaneously.

Five different material systems were explored at Intermolecular in less than a month: aluminum zinc oxide (AZO), indium tin oxide (ITO), indium zinc oxide (IZO), indium titanium oxide, and indium silicon oxide. HPC methods allowed for the discovery of a particular IZO composition range (between 5-15% of zinc oxide, 85-95% indium oxide) that shows resistivity comparable or slightly better than the ITO baseline at IM. However, the emissivity was measured to be 10% better while maintaining transparency levels similar to ITO at the same thicknesses. This improvement in emissivity makes IZO a very promising TCO material for low-E and electrochromic applications. IM’s baseline for ITO has resistivity of 350µΩ*cm and emissivity of 0.165 (16.5% of standard silver mirror). Unlike the crystallinity of ITO, IZO’s amorphous structure provides for a much more robust process window with good repeatability. The amorphous structure also makes IZO a well suited material for flexible PV applications.

Another advantage of using multi source PVD chambers as part of a HPC workflow is the ability to deposit multi-layer TCOs. Stacks of TCO-Metal-TCO films (T-M-T) were explored using only 1 source for the TCO and 1 for the metal. Resistivity, emissivity, and transparency showed a strong correlation to the thickness of the metal layer in the T-M-T stack, as would be expected by theory. Preliminary data already indicated a 75% improvement in resistivity and 33% improvement in emissivity, though with a 23% reduction in transmittance compared to an ITO single layer film.

Transparent conductive oxides (TCOs) have been extensively studied because they are one of the most important components for large area electronics devices such as solar cells, organic light-emitting diode (OLED), optical sensors or touch screens. In recent years, there is much interest in the OLED applications like large scale display, flexible display and smart phone and so on. Indium oxide doped with tin (In₂O₃:Sn, ITO) is known for a most typical material for a transparent electrode.

However, rare and expensive indium in ITO is also blocking the use of ITO. So it is necessary to find the substitute of ITO and zinc oxide is an excellent candidate. The group 3 elements (Al, Ga B and so on) doped zinc oxide is a promising TCO material for OLED anode because of its high thermal stability and chemical durability.

Recently, many oxide semiconductors as the active channel layer for transparent thin-film transistors (TFTs) and their electronic applications, such as drivers for organic light-emitting diodes and transparent displays have been investigated because of their excellent electrical and optical properties at room temperature. Among those, sputtering-produced amorphous indium-zinc-oxide (a-IZO) thin films exhibit high electron mobility even when they are deposited at room temperature. Also, they can be used both as a channel layer and as source/drain layers of TFTs. Up to recent dates, most of researches have mainly been focused on developing the fabrication method of a-IZO TFTs or improving the device performances, however, the electrical instability including the drain current-gate bias hysteresis should be considered for practical applications. If there is a large hysteresis in TFT devices, non-uniform brightness or flickering phenomenon will occur in driving the liquid crystal display. Generally, the voltage shift (ΔV_th) due to hysteresis of TFTs suggests that negative charge carriers are trapped at the channel/gate oxide interface or injected into the dielectric from the oxide channels. It is also known that metal ion vacancies of channel layer in oxide TFTs may act as charge trapping centers to cause the hysteresis. As for a-IZO TFTs, however, there have been scattered data in the literature and the exact mechanism responsible for the hysteresis phenomenon has not been clear yet.

In this study, we have investigated the hysteresis mechanism in a-IZO TFTs with the active channel consisting of two a-IZO thin layers (hereafter, referred to as “two-step a-IZO TFT”). The TFTs were fabricated with a bottom gate structure and the a-IZO channel layers were deposited on thermally oxidized Si substrates (gate) via RF sputtering by following the two-step deposition procedures. The 1^st a-IZO layer was deposited at a relatively low oxygen partial pressure (i.e., O₂/Ar < 5 %) and the 2^nd a-IZO deposition was accompanied without stopping the vacuum, only by increasing the oxygen partial pressure (i.e., O₂/Ar > 10 %). The forward and reverse sweep characteristics of the both of two-step and monolayer a-IZO TFTs were measured in the dark using a semiconductor parameter analyzer at room temperature. Capacitance-voltage characteristic of a-IZO TFTs were measured using an impedance analyzer. In addition, the time dependent electrical properties of a-IZO TFTs were measured. The experimental results showed that the voltage shift due to hysteresis could be significantly suppressed in two-step a-IZO TFTs as compared with conventional single-channel a-IZO TFTs.

Zinc oxide (ZnO)-based semiconductors as the active channel layer for thin film transistors (TFTs) recently have attracted much attention due to their excellent characteristics such as higher mobility than amorphous silicon, the ability to perform room-temperature deposition, and high transparency. However, most of the successful ZnO-based TFTs incorporate indium and gallium, such as indium zinc oxide (IZO), indium zinc tin oxide (IZTO), and indium gallium zinc oxide (IGZO), which are relatively rare on Earth. This makes those technologies easily subject to a material shortage. Recently, some researchers have reported experimental results which demonstrate new indium and gallium-free oxide semiconductors, such as aluminum zinc tin oxide (AZTO), magnesium zinc oxide (MZO), and titanium oxide (TiO_x), as another alternative channel layer for oxide TFTs.

In recent years, amorphous oxide semiconductors (AOSs) are attracted much attention due to high mobility, low temperature deposition, suitable for flexible display, transmission, and good uniformity. The thin film transistors with a-AZTO thin film as the active layer perform higher mobility and better reliability than conventional hydrogenated amorphous silicon TFT (a-Si: H TFT). In addition, the uniformity of a-AZTO TFT is also superior to Low Temperature Polycrystalline Silicon TFT (LTPS TFT). Therefore, the a-AZTO TFT s have the potential to replace a-Si: H TFTs and LTPS TFTs for Active Matrix Organic Light Emitting Display (AMOLED). In this study, we used rf sputter, which is compatible with industry application and integration, deposit a-AZTO active layer and then modulated the different processing oxygen flux, and discussed electrical and optical properties of the device impact.

This paper investigates the effect of DC and AC hot-carrier stress under light illumination for amorphous InGaZnO thin-film transistors (TFTs). Drain current-gate voltage (I_D-V_G) as well as capacitance-voltage (C-V) measurements are utilized to analyze the degradation mechanism. Illuminated DC hot-carrier stress leads to not only a negative parallel shift but also a C-V curve distortion at the off-state. This can be attributed to the asymmetric hole-trapping effect induced barrier-lowering near the drain side. To further verify the origin of the degradation behavior, AC bias with identical stress voltage is instead imposed on either gate terminal or drain terminal. It is deduced that hole-trapping phenomenon near the drain is dominated by the voltage across gate and drain, and is responsible for the degradation mechanism under illuminated hot-carrier stress.

Dye-sensitized solar cells have been studied intensively since the discovery of DSSCs in 1991, has paved the way to cell efficiency as high as 11%, allowing to foresee the possibility of obtaining cost efficient cells.[1] In this study, ZnO thin film have been growth on FTO glass which used for dye sensitized solar cells(DSSC) by electron-beam evaporation. While a great number of various deposition techniques were reported for Zinc Oxide(ZnO) thin films, e.g. R.F and D.C. sputtering, pulsed laser deposition, metal organic chemical vapor deposition, and others. most of the ZnO active layers in TFT have been deposited by physical vapor deposition methods.

Electron was caused in N-719 and get through photoelectron (TiO₂) and TCO. Electron loss occurs at each interface. Specially, TiO₂ electrode on FTO. Fig.1 show the various components of a DSSC. It is also shows the process flow of occurred electron in dye, and electron recombination in TiO₂ to FTO interface. One of the reason deposition ZnO passivating layer can prevent recombination effectively. In addition the interfacial contact properties between the semiconductor metal oxide layer and the transparent conducting oxide (TCO) have been considered to play a significant role in the enhancement of the photovoltaic performance of DSSCs. In theory, ZnO has wide band gap (larger than 3eV) also excellent electron collecting capability and mobility[2]. ZnO passivating layer at room temperature and the chamber pressure was kept below 5 10⁶ torr at different atmosphere O₂ gas flow. Electron-beam voltage was 8kv. The crystal structure and morphology were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), The transmittance of the film was examined using a UV-spectrometer. The conversion efficiency of the DSSC fabricated was measured using I-V solar stimulator.

In the present study, Zn_yCd_1-yS thin film was coated on the ITO glass with chemical bath deposition method, using zinc acetate and cadmium acetate as precursors. Dye-sensitized solar cell was prepared from the Zn_yCd_1-yS /ITO glass with Anthocyanin, which was extracted from the grape skin, as a dye. Pt-sputtered ITO glass was used as the counter electrode. The influences of zinc/cadmium ratio and reaction time on the performance of the prepared dye-sensitized solar cell were discussed. FESEM was used to characterize the surface microstructure and sectional thickness of the Zn_yCd_1-yS film . The absorption spectra of the Zn_yCd_1-yS film and Anthocyanin dye were recorded using UV-VIS spectrophotometer . The characteristic of the Anthocyanin dye was also analyzed by FTIR spectrophotometer. Photocurrent-voltage (I-V) measurements were performed using an electrochemical analyzer. According to the UV-VIS results, Anthocyanin dye has a significant absorption band within the wavelength of 400～700nm, which can enhance the visible light absorption of the Zn_yCd_1-yS film. The results that the dye-sensitized solar cell prepared from the Zn_0.2Cd_0.8S film exhibited the best performance. The open-circuit voltage, short-circuit current, and photo-to-electron power conversion efficiency are 0.695V, 1.408mA, and 4.07%, respectively.

The effects of deposition thickness of HfO₂ film prepared by atomic layer deposition on the electrical and reliability properties were reported. Scaling the physical thickness of HfO₂ dielectric did not linearly increase the capacitance due to a thicker interfacial SiO₂ layer through oxidation process in thermal annealing. Additionally, the degree of HfO₂ crystallization is increased after the thermal annealing as the thickness of HfO₂ film is increased, resulting in a higher dielectric constant for bulk HfO₂ film. The breakdown behaviors of HfO₂ gate dielectric film is also not scaled with the thickness, but is improved with the reduction of the thickness. Furthermore, the reliability characteristics of HfO₂ dielectric under unipolar AC stress were also evaluated. A longer dielectric breakdown lifetime is observed as compared to constant voltage stress. As the thickness of HfO₂ dielectric increases, a larger lifetime enhancement is detected due to the effective charge detrapping for thicker dielectrics under AC stressing.

The aim of this study is to explore the effect of titanium (Ti) doping on the growth of behavior, microstructure and optical characteristics of tungsten oxide (WO₃), which is an important material with a wide range of technological applications in optical and optoelectronic devices. W_0.80Ti_0.20O₃ thin films were fabricated using RF magnetron sputtering deposition onto silicon and optical grade quartz substrates in wide range of growth temperatures (25-500 ˚C). X-ray diffraction (XRD), high-resolution scanning electron microscopy (SEM), optical spectrophotometery and spectroscopic ellipsometry(SE) were performed to study the effect of temperature on the growth behavior, crystal structure, texturing, surface morphology, and optical properties of W_0.80Ti_0.20O₃ films. The results show that the effect of temperature is significant on the growth, structure and optical properties of W_0.80Ti_0.20O₃ films. XRD results indicate that the W_0.80Ti_0.20O₃ films grown up to a temperature of 400˚C are amorphous. A temperature of 500 oC is needed to obtain nanocrystalline W-Ti-O films. Annealing at 600˚C to 900˚C performed on the amorphous films indicate the formation of crystalline W_0.80Ti_0.20O₃ films. The SEM imaging analysis indicates that the phase transformations are accompanied by a characteristic change in surface morphology. SE analysis indicates the thickness of all the films is ~100 nm, which is in good agreement with the value obtained by other methods. Optical band gap of WO₃ is found to be affected by the Ti-doping. Spectrophotometry and SE analysis indicate that the effect of ultra-microstructure and grain-size was significant on the optical properties of W_0.80Ti_0.20O₃ films.

This paper investigates the gate bias induced threshold voltage (V_th) instability for p-type metal oxide semiconductor field effect transistors (p-MOSFETs) with HfO₂/Ti_xN_1-x gate stack. The experiment results indicate that for different nitride concentration of metal gate, the V_th shift has a contrary trend under positive and negative gate bias stress, respectively. Applying negative gate bias stress causes an increase in V_th shift with increasing nitride concentration of metal gate. This phenomenon is associated with amount of interface states caused by nitrogen diffusion from metal gate toward interface of Si/SiO₂. On the other hand, under the positive gate bias stress, the V_th shift has a gradual decrease while nitride concentration increases in metal gate. This contrary tendency can attribute to the electron trapping effect, which is dependent on amount of existing defects in high-k bulk with different nitride concentration of metal gate.

films’ optical properties, the transmission, reflection, and absorption spectra were measured, and certain plasmonic absorption was identified. The results were then co-related with those obtained from the heating measurement. It was found that the heating enhancement due to the incorporation of Ag particles is significant. The largest temperature increment can reach 45 ^oC. The increments were dependent on the number of Ag layer, heat treatment conditions, and the oxide matrix. A theory was proposed to explain the enhanced light absorption and, therefore, the enhanced heating effect under light irradiation.

The plasma of an ICP-CVD system attached with four internal antennas was used to deposit doped and un-doped Si thin films. Hydrogenated microcrystalline silicon (μc-Si:H) films were prepared under various RF power, while the flow ratio of SiH₄/H₂ was fixed at 1/4. During deposition, an OES (optical emission spectrometer) and a plasma probe were used to characterize the conditions of plasma. The crystalllinity and opto-electrical properties of the Si:H films were investigated using Raman scattering spectroscopy, XRD, Hall effect measurement system, and UV-Vis photometer. It is found that the crystallinity of μc-Si:H film was significantly affected by plasma density which was increased with the increase of the power. This could be caused by the increase of I*_SiH3/I_Ha. It is also found the plasma potential would decrease with the increase of power, while the plasma density would increase with the increase of power. The carrier density, mobility, and photoconductivity were found related to the plasma potential and density which might affect defect density in the films.

Boron-doped amorphous carbon (a-C:B) films were deposited on n-type silicon (n-Si) wafers using reactive radio-frequency (RF) chemical vapor deposition. A boron target was used as the dopant source, and a mixture of pure methane (CH₄) and argon (Ar) gases with flow rates of 2 and 10 sccm, respectively, was selected as the precursor gas. Five kinds of a-C:B films were prepared with RF powers of 100, 200, 300, 400, and 500 W. The substrate temperature and working pressure were set at 298 K and 6 Pa, respectively. The thicknesses of a-C:B films were measured using field emission scanning electron microscopy (FESEM). Alternatively, the characteristics of a-C:B films were analyzed by X-ray photoelectron spectrometer (XPS) and Raman scattering spectra (RSS). After the a-C:B/n-Si junction was sputtered with gold (Au) and aluminum (Al) electrodes, the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Au/a-C:B/n-Si/Al heterojunction devices were measured.

FESEM results show that all the thicknesses of a-C:B films are about 100 nm. XPS analyzed results reveal that the boron atoms are successfully doped into amorphous carbon films, and the boron content increases from 0.02 to 28.87 at.% as the RF power increases from 100 to 500 W. The RSS data of a-C:B films indicate that the ratio of the integrated intensity of the D band to that of the G band (ID/IG) increases with increasing the RF power from 100 to 300 W, but decreases with increasing the RF power from 300 to 500 W. It implies that the a-C:B film prepared with the RF power of 300 W has a relatively higher graphitization degree. Our analyzed results also show that all the I-V characteristics of Au/a-C:B/n-Si/Al heterojunction devices exhibit the rectifying behavior. When the a-C:B film was prepared with the RF power of 300 W, the Au/a-C:B/n-Si/Al heterojunction device displays the best rectifying I-V characteristics, and its ideality factor is about 1.40. The C-V measurement under the frequency of 1 kHz shows that as the a-C:B film was prepared by the RF power of 300 W, the built-in voltage of the Au/a-C:B/n-Si/Al device is about 0.2 V.

An important step towards optimization of InN/GaN based devices is the identification of the structural characteristics of the corresponding interfaces since the favourable bonding configurations determine the materials polarity and consequently the direction of spontaneous polarization. We have addressed this issue through empirical potential calculations on InN/GaN interfaces comprising misfit dislocations [1]. An appropriately parameterized Tersoff interatomic potential [2] was implemented and energetic calculations were performed on interfaces of III- and N- polarity, lying at the single- or double bonds and having a wurtzite or zinc blende stacking sequence in accordance with high resolution transmission electron microscopy observations. Based on these results III-polarity interfaces, cutting single bonds are energetically favourable.

In our present study, additional calculations are performed on subcritical thickness InN/GaN QWs, which exhibit lower dislocation densities as well as reduced InN decomposition and are currently implemented in the fabrication of near-UV light emitting diodes [3,4]. Ab initio calculations are performed under modified pseudopotentials, accurately reproducing the InN and GaN band gap values, on supercells comprising 1 monolayer (ML) thick InN elastically strained in 5 nm thick GaN barriers having a wurtzite or zinc blende stacking at the interface. The former is found to be energetically favourable. Subsequent calculations on supercells comprising 1 ML thick InN in 8 and 11 nm thick GaN barriers as well as 3 ML InN in 11 nm thick GaN having a wurtzite stacking, depicted a variation in III-N bond lengths. This variation become more significant as the barrier thickness decreases or the QW thickness increases. Hence the strain and consequently piezoelectric polarization are modified. The latter is attested by density of states calculations, which show a vast decrease of the band gap when 5 nm thick barriers are considered, while a significant decrease is also recorded at the 3 ML InN / 11 nm GaN barrier heterostructure in comparison with the 1 ML InN supercell. Our results scrutinize recent experimental observations [3,4] and could prove beneficial for tailoring the optoelectronic properties of InN/GaN QWs.

[1] J. Kioseoglou et al., J. Mater. Sci. 43, 3982 (2008)

[2] J. Kioseoglou et al., Phys. Stat. Sol. (b) 245, 1118 (2008)

[3] E. Dimakis et al., Phys. Stat. Sol. (a) 205, 1070 (2008)

[4] A. Yoshikawa et al., J. Vac. Sci. Technol. B 26, 1071 (2008)

[5] Work supported by EC under the 7^th European Framework Project DOTSENSE (Grant No.

Stabilized metal silicides with low barrier for ohmic contact or high barrier for rectification has advantages for nanometer scaled device fabrication. The use of silicide instead of impurity doped silicon for drain and source has advantages in terms of processing temperature and much less trap creation during the fabrication. Ultra shallow junction can be formed easily with the metals having low diffusion coefficient in silicon. Low barrier of metal-silicide on source/drain is key point for ultrascaled complementary metal/oxide/semiconductors in future technology. On the other side Schottky barrier as a gate terminal may suffer from barrier inhomogeneity. Because of that, much better performance of SB require careful I-V analysis which gives some of suggestions related to material selection and fabrication parameters. Inhomogeneity of Schottky barrier at room temperature widely studied during the last decade. In this study, the temperature dependence of barrier distribution below room temperature presented for the first time.

With this context, the rectification effect of Er-silicide on p-Si was investigated. Sputter tehnique is used for deposition and Er-Silicide thermally activated by annealing above 300 ºC under the nitrogen atmosphere. I-V-T measurement of multiple diodes was analysed for the barrier inhomogeneity of Er-Silicide/p-Si junctions.