bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Manganese Source Material on Characteristics of Zn2SiO4:Mn Phosphor Particles Prepared by Spray Pyrolysis
Authors: Kang Yun Chan
Published: July 2005

The type of manganese material used as an activator source affected the luminous characteristics of Zn2SiO4:Mn phosphor particles in spray pyrolysis. The prepared Zn2SiO4:Mn particles had different optimum post-treatment temperatures and reduction conditions for obtaining the maximum photoluminescence intensity from the manganese source material used. The particles prepared from manganese nitrate and sulfate had higher photoluminescence intensities than the commercial product prepared by solid-state reaction method after post-treatment at 1200°C without using a reduction process. However, the maximum photoluminescence intensity under vacuum ultraviolet excitation was obtained from the particles prepared from manganese chloride, post-treated at 1120°C for 5 h and reduced at 775°C, which was 10% higher than that of the commercial product. Manganese source material also affected the decay time (τ10) of the Zn2SiO4:Mn phosphor particles. The manganese chloride was favored for the formation of the phosphor particles having a short decay time and high brightness under vacuum ultraviolet excitation.
Analysis of Static and Dynamic Performance of Short-Channel Double-Gate Silicon-on-Insulator Metal-Oxide-Semiconductor Field-Effect Transistors for Improved Cutoff Frequency
Authors: Kranti Abhinav , Chung Tsung Ming , Raskin Jean-Pierre
Published: July 2005

A comprehensive analysis of the static and dynamic characteristics of deep submicron double-gate (DG) and single-gate (SG) silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) is presented, based on two-dimensional (2D) numerical simulations for high-frequency analog applications. Results from the static analysis show that a DG MOSFET offers excellent performance with respect to short-channel immunity, drain current enhancement and improvement in transconductance, Early voltage and voltage gain. We also analyze the impact of volume inversion (VI) on the performance of DG devices under saturation conditions, and investigate, in detail, the level of current enhancement and the bias conditions under which it can be achieved. Results show that a current as high as 15 times that of single-gate (SG) MOSFETs can be achieved in DG devices at a transconductance-to-current ratio of 25 V-1. Analysis of the dynamic part shows that due to the dual-gate structure, DG devices offer nearly twice the gate-source capacitance as compared to SG devices, thus limiting the cutoff frequency at higher gate voltages and longer channel lengths. At shorter channel lengths (L≤50 nm) and low gate overdrive voltages (<400 mV), DG devices show a significant improvement in cutoff frequency compared to SG devices, thus making double-gate SOI MOSFETs potential candidates for high-frequency analog applications.
Selectable Logarithmic/Linear Response Active Pixel Sensor Cell with Reduced Fixed-Pattern-Noise Based on Dynamic Threshold MOS Operation
Authors: Terauchi Mamoru , Hamasaki Atsushi , Suketa Arinori
Published: July 2005

A selectable logarithmic/linear response active pixel sensor cell with reduced fixed-pattern-noise is proposed. It is composed of four dynamic threshold metal-semiconductor-oxide field-effect transistors (DTMOSs), which have inherently fewer characteristic fluctuations than conventional bulk counterparts. Therefore this proposed active pixel sensor cell is expected to reduce fixed-pattern-noise as compared with that of a device composed of bulk metal-oxide-semiconductor field effect transistors (MOSFETs) without any external noise reduction circuitry particularly in the logarithmic response mode. The effectiveness of the proposed sensor cell is partly experimentally verified using test devices that simulate the readout portion of the proposed sensor cell.
Liquid Crystal Anamorphic Lens
Authors: Ye Mao , Yokoyama Yoshitaka , Sato Susumu
Published: July 2005

A liquid crystal (LC) anamorphic lens is realized using an LC cell with a transparent electrode and a divided electrode with a hole in the center. By applying appropriate potentials on the divided electrode, the LC cell behaves like an optical lens with astigmatic properties. An incident plane lightwave experiences a nearly elliptical profile of phase retardation. The astigmatism is also electrically controllable.
Device Design Consideration for Vth-Controllable Four-Terminal Double-Gate Metal-Oxide-Semiconductor Field-Effect Transistor
Authors: Masahara Meishoku , Liu Yongxun , Sakamoto Kunihiro , Endo Kazuhiko , Sekigawa Toshihiro , Matsukawa Takashi , Suzuki Eiichi
Published: July 2005

The optimum device design for a threshold-voltage (V
th)-controllable four-terminal double-gate metal-oxide-semiconductor field-effect transistor (4T-DGFET) has been investigated by device simulation. The effects of the device parameters, e.g., workfunction (φm) of the double gate, gate oxide thickness (T
ox), effective gate length (L
eff), and the range of the second gate voltage (V
g2) on 4T-DGFET performance have been systematically examined. Simulation results show that lowering φms and increasing the second gate oxide thickness (T
ox2) are preferable for the improvement of 4T-DGFET performance. The short channel effects (SCEs) for the 4T-DGFET have also been investigated in terms of V
th roll-off, degradation in subthreshold slope (S) and back-gate-effect factor (γ). It is shown that all the SCEs become severer with increasing T
ox2. As a result, in the case of the ultrashort L
eff regime, a thick T
ox2 is not so preferable. In particular, under the limited V
g2 condition, a thin T
ox2 is advantageous for enhancing the drive current due to the high V
th controllability and SCE immunity.
Improvement of Oxidation-Induced Ge Condensation Method by H+ Implantation and Two-Step Annealing for Highly Stress-Relaxed SiGe-on-Insulator
Authors: Sadoh Taizoh , Matsuura Ryo , Ninomiya Masaharu , Nakamae Masahiko , Enokida Toyotsugu , Hagino Hiroyasu , Miyao Masanobu
Published: July 2005

The effects of the H+ implantation (8.1 keV and 0–5×1016 cm-2) and two-step annealing (1st: 500°C for 30 min, 2nd: 850°C for 60 min) on the stress relaxation of c-Si1-x
Ge
x
buffer layers on insulator (SGOI) formed by the oxidation-induced Ge condensation process have been investigated. The stress relaxation of SGOI during oxidation (1100°C) was significantly improved by high-dose (>1015 cm-2) H+ implantation. However, the oxidation was also enhanced by the implantation. The enhanced oxidation was completely suppressed by the two-step annealing before oxidation. The enhanced stress relaxation was attributed to the enhanced gliding of the c-Si1-x
Ge
x
layers on SiO2. This newly developed combination method of H+ implantation, the two-step annealing, and the oxidation-induced Ge condensation will be a powerful tool in the fabrication of highly relaxed SGOI for growth of strained Si layers.
Modeling Geometry-Dependent Floating-Body Effect Using Body-Source Built-In Potential Lowering for SOI Circuit Simulation
Authors: Su Pin , Lee Wei
Published: July 2005

This paper presents a compact silicon-on-insulator (SOI) model to capture the geometry-dependent floating-body effect using the body-source built-in potential lowering approach. This physically accurate model circumvents the modeling challenge imposed by the trend of the coexistence of partial-depletion (PD) and full-depletion (FD) devices in a single SOI chip by considering short-channel, reverse short-channel and reverse narrow-width floating-body effects. The implication on circuit simulation, under the unified Berkeley short-channel IGFET model-silicon-on-insulator (BSIMSOI) framework, has also been addressed. This geometry-dependent body-source built-in potential lowering model will further enhance the device design of scaled SOI complementary metal-oxide-semiconductor (CMOS) below 100 nm.
Influence of Charge Traps within HfSiON Bulk on Positive and Negative Bias Temperature Instability of HfSiON Gate Stacks
Authors: Fujieda Shinji , Kotsuji Setsu , Morioka Ayuka , Terai Masayuki , Saitoh Motofumi
Published: July 2005

We characterized how positive and negative bias temperature instabilities (PBTI and NBTI) occur in HfSiON gate stacks. The PBTI was confirmed to be suppressed by using amorphous (a-) HfSiON instead of crystallized (c-) HfSiON. The a-HfSiON reduced the capture cross-section and lowered the density of electron traps, which explains the suppression of the PBTI. The different trap parameters for a-HfSiON and c-HfSiON suggest that the electron traps of these structures have different origins. The PBTI of a-HfSiON gates occurred through electron trapping without generation of interface traps, while the NBTI of a-HfSiON gates occurred through generation of interface traps and positive oxide charges. Furthermore, it was found that the NBTI of a-HfSiON gates also involves electron trapping. Additionally, the subthreshold slope decreased under positive BT stress. We attribute these characteristic BTI behaviors of HfSiON gates to the influence of charge traps that are present within the HfSiON bulk.
Evaluation of Interface States Density and Minority Carrier Generation Lifetime for Strained Si/SiGe Wafers Using Transient Capacitance Method
Authors: Wang Dong , Ninomiya Masaharu , Nakamae Masahiko , Nakashima Hiroshi
Published: July 2005

Interface states density (N
ss) and minority carrier generation lifetime (τg) were evaluated in detail for strained Si/SiGe wafers by deep-level transient spectroscopy and metal-oxide-semiconductor transient capacitance methods. N
ss shows a nondependence on strained Si thickness (d
Si) within a critical thickness and a clear dependence on Ge fraction (Ge%). τg shows a strong dependence on both d
Si and Ge%. The reasons for these dependences are discussed in detail.
Study of Gate Length Dependence of Two-dimensional Carrier Profile in N-FET by Scanning Tunneling Microscopy
Authors: Fukutome Hidenobu , Aoyama Takayuki , Arimoto Hiroshi
Published: July 2005

We measured the two-dimensional carrier profiles of n-type field effect transistors (n-FETs) with various gate lengths (Lg) by scanning tunneling microscopy. The extension overlap and the distribution of the depletion layers were evaluated to clarify that the measured carrier profiles were consistent with the roll-off characteristic of corresponding transistors. The effect of a pocket implant on a long transistor appeared where the lateral depletion width was locally shorter than the vertical one. In the n-FET with a gate length less than 40 nm, the effect of the pocket impurities from the opposite side mainly appeared as a reduction in the extension overlap in the deep region. Although the presence of this pocket increased the top channel concentration, the short length of the effective channel resulted in the spread of the depletion layer in the deep-channel region via the two-dimensional effect.
Low-Temperature Formation of Poly-Si1-xGex (x: 0–1) on SiO2 by Au-Mediated Lateral Crystallization
Authors: Kanno Hiroshi , Aoki Tomohisa , Kenjo Atsushi , Sadoh Taizoh , Miyao Masanobu
Published: July 2005

The Au-mediated low-temperature (400°C) crystallization of amorphous-Si1-x
Ge
x
(x: 0–1) on SiO2 has been investigated. A growth velocity exceeding 20 µm/h was obtained for samples in the entire range of Ge fractions (x: 0–1), although it decreased with increasing Ge fraction. These values are much higher than those obtained by conventional Ni-mediated crystallization. As a result, strain-free poly-Si1-x
Ge
x
(x: 0–1) with large areas (>20 µm) were obtained at a low temperature (400°C). This newly developed method has a high potential for fabricating poly-Si1-x
Ge
x
(x: 0–1) on a glass substrate.
Contactless Characterization of Fixed Charges in HfO2 Thin Film from Photoreflectance
Authors: Sohgawa Masayuki , Yoshida Masato , Naoyama Takuji , Tada Taizou , Ikeda Kouji , Kanashima Takeshi , Fujimoto Akira , Okuyama Masanori
Published: July 2005

Fixed oxide charges in HfO2 thin films have been characterized by photoreflectance spectroscopy (PRS). HfO2 films were deposited on Si by pulsed laser deposition (PLD) in N2, O2 and a mixture of these gases. PRS spectral intensity decreases with increasing positive charge in a film. HfO2 deposited in N2 has larger positive charges than that deposited in O2 because of smaller PRS spectral intensity of the former. It is confirmed by ArF laser irradiation that this positive charge is caused by oxygen defects in HfO2. Moreover, the effects of rapid thermal annealing (RTA) on HfO2/Si have been evaluated by PRS. The PRS spectral intensity becomes maximum by RTA at 600°C in N2 or O2. It is suggested that the suitable temperature for the RTA of the HfO2/Si structure prepared by PLD is 600°C.
Growth of Periodic SiO2 Nanostructures Using a 157 nm F2 Laser
Authors: Takao Hiromitsu , Okoshi Masayuki , Inoue Narumi
Published: July 2005

Periodic nanostructures on SiO2 films were fabricated by Fresnel diffraction of a mask with a square aperture using the photochemical deposition method. In this method, an F2 laser beam at a low laser fluence simultaneously irradiates a silicone rubber target and a substrate through the mask. The SiO2 nanostructures are photochemically grown according to the intensity distribution at room temperature. The fringe period of the nanostructure formed on the substrate corresponded to the calculated results, and can be reduced up to ∼200 nm by decreasing the distance from the mask to the substrate.
Transient Charging and Relaxation in High-k Gate Dielectrics and Their Implications
Authors: Lee Byoung Hun , Young Chadwin , Choi Rino , Sim Jang Hwan , Bersuker Gennadi
Published: July 2005

Recent results on device instability indicate that the methodologies developed for electrical characterization of metal oxide semiconductor (MOS) devices with SiO2 gate dielectric may not be sufficiently accurate for high-k devices. While the physical origin of the instabilities in high-k devices is yet to be identified, it is found that many of the abnormal electrical characteristics of high-k devices can be explained by assuming fast and slow transient chargings in high-k dielectric. In this paper, transient charging effects in high-k gate dielectrics are reviewed and their implications on test methodologies are discussed.
Trapping/De-Trapping Gate Bias Dependence of Hf-Silicate Dielectrics with Poly and TiN Gate Electrode
Authors: Sim Jang Hoan , Choi Rino , Lee Byoung Hun , Young Chadwin , Zeitzoff Peter , Kwong Dim-Lee , Bersuker Gennadi
Published: July 2005

Constant voltage stress induced V
th shift and its detrapping characteristics under the negative gate bias has been extensively investigated with HF-silicate dielectrics with poly and TiN gate electrode. The threshold voltage shift in negative-channel metal-oxide semiconductor (NMOS) transistors under the positive gate bias stress is found to be associated mostly with the reversible electron trapping. A proper negative bias can be used to de-trap the electrons accumulated during the positive stress. However, an aggressive de-trapping can cause an additional V
th instability due to the excessive de-trapping of existing charge or additional hole trapping at the interface with poly gate. TiN metal gate is found to be more stable with de-trapping negative gate bias. To de-trap the electrons accumulated in the dielectric during the positive constant voltage stress (CVS), the negative bias and its duration should be chosen very carefully to avoid the additional charging associated with the hole trapping.
Novel Extraction Method for Size-Dependent Mobility Based on BSIM3-Like Compact Model
Authors: Tanaka Takuji , Goto Ken-ichi , Nakamura Ryou , Satoh Shigeo
Published: July 2005

We applied a BSIM3-like compact model in order to analyze size dependent low field mobility in MOSFETs. By using the newly proposed extraction method, we have successfully extracted the gate length dependence of mobility degradation due to halo doping and the mobility enhancement due to mechanical stress. Moreover, parasitic resistance at source and drain R
sd has been accurately extracted in a variable mobility case. The new method is applicable to wide ranges of device sizes, structures and materials.
Thermal Stability and Electrical Properties of (La2O3)1-x(Al2O3)x Composite Films
Authors: Fujitsuka Ryota , Sakashita Mitsuo , Sakai Akira , Ogawa Masaki , Zaima Shigeaki , Yasuda Yukio
Published: July 2005

(La2O3)1-x
(Al2O3)
x
composite films (La2O3:Al2O3 = 100:0, 80:20, 67:33, 50:50) were synthesized using pulsed laser deposition. We investigated their thermal stability and electrical properties as high dielectric constant gate dielectric films. La2O3 (an Al2O3 content of 0%) films were uniformly crystallized as La-silicate after rapid thermal annealing (RTA) at 1000°C for 15 s in an N2 ambient. We found that the addition of Al2O3 suppresses crystallization, and amorphous structures are retained in the samples with an Al2O3 content of 33% or greater. Furthermore, Al2O3 addition suppresses diffusion of Si into upper composite films during RTA. The smallest capacitance equivalent oxide thickness of 1.2 nm was achieved for a sample with an Al2O3 content of 20% and with leakage current density of 3.9×10-3 A/cm2 at + 1 V relative to the flat band voltage.
Tunable-Focus Cylindrical Liquid Crystal Lenses
Authors: Lin Yi-Hsin , Ren Hongwen , Fan-Chiang Kuan-Hsu , Choi Wing-Kit , Gauza Sebastian , Zhu Xinyu , Wu Shin-Tson
Published: July 2005

Tunable-focus cylindrical liquid crystal lenses of four different electrode configurations are analyzed. Simulation results show that the proposed devices can have different focal lengths even if they have the same aperture size. A good agreement between experiment and simulation results is obtained. The imaging property of one of the cylindrical liquid crystal lenses is also demonstrated.
Accuracy of Secondary Ion Mass Spectrometry Depth Profiling for Sub-keV As+ Implantation
Authors: Eto Takanori , Shibahara Kentaro
Published: July 2005

The depth profiling of sub-keV As+ implantation for sub-10 nm junction formation was investigated. The tail slope of profiles measured by secondary ion mass spectrometry (SIMS) using 300 eV Cs+ was much gentler than that of simulated profiles. Model calculation considering the mixing effect due to Cs+ bombardment during SIMS measurement explained the SIMS tail well. This implies that accurate As depth profiling by simply lowering primary Cs+ energy is difficult because of ion gun limitations. At the surface region, a 1.4-nm-thick surface layer was found. This layer is considerably thick for the sub-10 nm junction and is thicker than 0.4 nm for 5 keV implantation.
Ultra-Short Pulse Current–Voltage Characterization of the Intrinsic Characteristics of High-κ Devices
Authors: Young Chadwin D. , Zhao Yuegang , Pendley Michael , Lee Byoung Hun , Matthews Kenneth , Sim Jang Hoan , Choi Rino , Brown George A. , Murto Robert W. , Bersuker Gennadi
Published: July 2005

An ultra-short pulse current–voltage (I–V) measurement technique has been applied to high-κ gate transistors to investigate the effects of fast transient charging. It is shown that the fast electron trapping may contribute to the degradation of transistor performance (i.e., low mobility) observed with direct current (DC) characterization methods, as well as pulse techniques in the tens of microseconds range and above. In particular, in the samples with significant electron trapping, the drain current in the saturation regime is shown to improve by up to 40% from its DC values when the characterization is performed with pulse I–V measurements in the nanosecond range.
Breakdown Mechanisms and Lifetime Prediction for 90-nm-Node Low-Power HfSiON/SiO2 CMOSFETs
Authors: Terai Masayuki , Yabe Yuko , Fujieda Shinji , Morioka Ayuka , Kotsuji Setsu , Iwamoto Toshiyuki , Saitoh Motofumi , Ogura Takashi , Saito Yukishige , Watanabe Hirohito
Published: July 2005

The mechanisms of gate leakage current and that of time dependent dielectric breakdown (TDDB) failure of HfSiON/SiO2 gate dielectrics having an equivalent oxide thickness of 1.6 nm were investigated. The leakage current mechanism was found to be different for low and high electric fields, which we attribute to the difference in barrier height between interfacial SiO2 and HfSiON. The mechanism of TDDB also proved to be different for low and high electric fields. Accordingly, TDDB lifetime must be evaluated in the low-gate-bias region, where the leakage current mechanism is the same as that of the actual FET operating voltages. A system for detecting defect generation using an emission microscope was developed, enabling low-bias TDDB measurements of large-gate-area transistors. Through this investigation, it was predicted that HfSiON/SiO2 has much more than 10 years' TDDB reliability.
Green and Ultraviolet Emissions From Anatase TiO2 Films Fabricated by Chemical Vapor Deposition
Authors: Najafov Hikmat , Tokita Shuji , Ohshio Shigeo , Kato Ariyuki , Saitoh Hidetoshi
Published: July 2005

Luminescence properties of anatase TiO2 films grown on sapphire substrates by atmospheric chemical vapor deposition have been investigated over a wide temperature range of 20 K to 300 K. An intense green emission band associated with localized exciton recombination has been observed at low temperatures under photoexcitation. The emission exhibited temperature quenching with an activation energy of ∼48 meV. The shape of the emission spectrum was considerably modified upon electron beam excitation. The principal feature of this modification is a reversible redistribution of the spectrum intensity, which causes the appearance of a new UV emission band at high acceleration voltages. Details of the mutual relationship between the green and UV emission processes are considered in terms of the linear coupling configuration coordinate model. We propose that the temperature quenching of green emission is attributed to a combination of various thermally stimulated processes within the configuration coordinate diagram and energy migration through the excited state of the UV emission.
Substrate Leakage Current in InGaP/GaAs Heterojunction Bipolar Transistors
Authors: Chang Yang-Hua , Chang Zhi-Juan , Hsieh Yi-Jing
Published: July 2005

Substrate leakage current in InGaP/GaAs heterojunction bipolar transistors (HBTs) has been observed. For a substrate thickness of 100 µm and an emitter area of 60 µm2, the parasitic current is on the order of 10-8 A. The current flowing between the collector terminal and the substrate can be decomposed into linear and parabolic components. The parabolic dependence is also observed in Medici simulation. A theoretical derivation based on electron drift in the substrate shows parabolic dependence on applied voltage, consistent with our measurement and Medici simulation. In addition, it has been found that the current is inversely proportional to the cube of substrate thickness. To account for this substrate parasitic effect, a modification of the vertical bipolar inter-company (VBIC) model is proposed.
High Temperature Performance and Low Frequency Noise Characteristics of AlGaN/GaN/AlGaN Double Heterostructure Metal-Oxide-Semiconductor Heterostructure Field-Effect-Transistors with Photochemical Vapor Deposition SiO2 Layer
Authors: Wang Chun-Kai , Chang Shoou-Jinn , Su Yan-Kuin , Chiou Yu-Zung , Kuo Cheng-Huang , Chang Chia-Sheng , Lin Tien-Kun , Ko Tsun-Kai , Tang Jing-Jou
Published: July 2005

High quality SiO2 films were successfully deposited onto AlGaN using photochemical vapor deposition (photo-CVD). The interface state density, D
it, of photo-CVD SiO2 was estimated to be only 1.1×1011 cm-2eV-1 at room temperature and still only 3.5×1012 cm-2eV-1 even at 175°C. With a 1 µm gate length, it was found that the maximum saturated drain-source current (I
ds), maximum transconductance (g
m) and gate voltage swing (GVS) of the AlGaN/GaN/AlGaN double heterostructure metal-oxide-semiconductor heterostructure field-effect-transistors (MOS-HFETs) fabricated were 755 mA/mm, 95 mS/mm and 8 V, respectively. Even at 300°C, the maximum saturated I
ds and maximum g
m of the MOS-HFETs fabricated were still kept at 527 mA/mm and 77 mS/mm, respectively. Furthermore, from the low frequency noise power spectrum, it was found that noise power density of the AlGaN/GaN/AlGaN double heterostructure was lower and presented pure 1/f noise with smaller trapping effects than conventional structures.
High Performance 0.1 µm GaAs Pseudomorphic High Electron Mobility Transistors with Si Pulse-Doped Cap Layer for 77 GHz Car Radar Applications
Authors: Kim Sungwon , Noh Hunhee , Jang Kyoungchul , Lee JaeHak , Seo Kwangseok
Published: July 2005

In this study, 0.1 µm double-recessed T-gate GaAs pseudomorphic high electron mobility transistors (PHEMT's), in which an InGaAs layer and a Si pulse-doped layer in the cap structure are inserted, have been successfully fabricated. This cap structure improves ohmic contact. The ohmic contact resistance is as small as 0.07 Ωmm, consequently the source resistance is reduced by about 20% compared to that of a conventional cap structure. This device shows good DC and microwave performance such as an extrinsic transconductance of 620 mS/mm, a maximum saturated drain current of 780 mA/mm, a cut-off frequency fT of 140 GHz and a maximum oscillation frequency of 260 GHz. The reverse breakdown is 5.7 V at a gate current density of 1 mA/mm. The maximum available gain is about 7 dB at 77 GHz. It is well suited for car radar monolithic microwave integrated circuits (MMICs).
Transconductance Linearity Improvement of Enhancement-Mode Pseudomorphic HEMT with High Gate Forward Turn-On Voltage
Authors: Jang Kyoungchul , Lee Jaehak , Kim Sungwon , Lee Jongwon , Seo Kwangseok
Published: July 2005

In this paper we discuss the sources of the transconductance reduction of enhancement-mode pseudomorphic high electron mobility transistor (E-pHEMT) at a high gate bias and methods of improving the transconductance at a high gate bias. E-pHEMT usually suffers from severe transconductance reduction at a high gate bias. Our simulation showed that this reduction is mainly due to the low channel carrier density and high access resistance of the ungated region rather than the parasitic MESFET phenomenon. An epi structure that facilitates electron transfer through the barrier layer of the ungated region and self align gate (SAG) process lead to an improvement in transconductance linearity.
Gate Leakage Reduction Mechanism of AlGaN/GaN MIS-HFETs
Authors: Kikuta Daigo , Takaki Ryohei , Matsuda Junya , Okada Masaya , Wei Xin , Ao Jin-Ping , Ohno Yasuo
Published: July 2005

The gate leakage reduction mechanism of AlGaN/GaN metal-insulator-semiconductor (MIS) heterostructure field-effect transistors (HFETs) is investigated and compared with those of three types of HFET, namely; a conventional HFET, a standard MIS-HFET and a specially prepared MIS-HFET with a metal interlayer. It is found that the resistance of the AlGaN layer with an insulator deposited on its surface is much higher than that of the AlGaN layer with a metal. From the fitting of transconductance-frequency characteristics, the resistance of the insulator-deposited AlGaN layer is about 5 orders of magnitude higher than that of the metal-deposited AlGaN layer. From dc measurements, the resistance of the insulator-deposited AlGaN layer at a negative gate bias is higher than that of the insulator layer. From these results, it can be concluded that gate leakage is suppressed by the high resistance of the AlGaN layer in the MIS-HFET at a negative gate bias.
Growth of AlGaN/GaN Quantum Wire Structures by Radio-Frequency-Radical-Assisted Selective Molecular Beam Epitaxy on Prepatterned Substrates
Authors: Sato Taketomo , Oikawa Takeshi , Hasegawa Hideki
Published: July 2005

The feasibility of the selective molecular beam epitaxy (MBE) growth of AlGaN/GaN quantum wire (QWR) structures on prepatterned substrates is investigated. The detailed studies on growth features have revealed that size-reducing selective growth is possible on mesa patterns having the <11-20>-orientation, but not on those having the <1-100>-orientations. The behavior reflects complex growth kinetics on high-index crystalline facets. The lateral wire width of QWR structures formed selectively on a top mesa can be controlled by adjusting the growth thickness and the initial size of mesa patterns. From cathodoluminescence (CL) measurements, emission from the embedded AlGaN/GaN QWR structure has been clearly identified.
Epitaxial Growth of Al-Doped β-FeSi2 on Si by Ion Beam Synthesis
Authors: Maeda Yoshihito , Terai Yoshikazu , Itakura Masaru
Published: July 2005

Ion-beam-synthesized (IBS) β-FeSi2/Si(100) heterojunctions were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Clear epitaxial growth of β-FeSi2 on Si(111) and large crystal domains laterally grown on the surface were demonstrated in Al-doped samples. The optical processes near the heterojunction were examined by photoluminescence spectra measured on the different optical configurations. The epitaxial growth due to Al doping was found to be effective in reducing the density of nonradiative recombination centers and enhancing an electron-hole injection. Solid phase epitaxy (SPE) of Si taking place at the Al-doped interface was found to be the dominant contribution to lateral growth on the surface and epitaxial growth of β-FeSi2.
Near-Ultraviolet InGaN/GaN Light-Emitting Diodes Grown on Patterned Sapphire Substrates
Authors: Wang Woei-Kai , Wuu Dong-Sing , Shih Wen-Chung , Fang Jau-Shing , Lee Chia-En , Lin Wen-Yu , Han Pin , Horng Ray-Hua , Hsu Ta-Cheng , Huo Tai-Chan , Jou Ming-Jiunn , Lin Aikey , Yu Yuan-Hsin
Published: July 2005

We describe the microstructure and optical properties of near-ultraviolet InGaN-GaN light-emitting diodes (LEDs) fabricated onto conventional and patterned sapphire substrates (PSSs) using metalorganic chemical vapor deposition. The PSS LED with an optimized hole depth (1.5 µm) shows an improvement of the room-temperature photoluminescence intensity by one order of magnitude compared with that of the conventional LED. As much as a 63% increased light emission intensity of the PSS LED was obtained at a forward current of 20 mA. For a typical lamp-form PSS LED (at 20 mA), the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The increase of the output power could be partly due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, which was further confirmed by the transmission-electron-microscopy and etch-pit-density studies for the GaN-on-PSS samples. Moreover, the emitted light scattering at the GaN/PSS interface could also contribute to the enhancement of light extraction efficiency.
High-Power GaN-Based Light-Emitting Diodes with Transparent Indium Zinc Oxide Films
Authors: Uang Kai-Ming , Wang Shui-Jinn , Chen Shiue-Lung , Wu Chin-Kun , Chang Shu-Cheng , Chen Tron-Min , Liou Bor-Wen
Published: July 2005

Large-area (0.6 mm×0.6 mm–1.5 mm×1.5 mm), high-power GaN-based blue-light-emitting diodes (LEDs) with an indium zinc oxide (IZO) overlay as a transparent conduction layer (TCL) and the effects of the overlayer on light output power (Lop) improvement are investigated. Experimental results show that sputter-deposited IZO TCLs with thicknesses in the range of 100–500 nm have a low resistivity ranging from 12.1–3.1×10-4 Ω-cm and a transparency ≥80% in the visible light range. The benefit obtained from the use of an IZO TCL is much more profound in LEDs of larger chip size; in addition, the optimum IZO TCL thickness is approximately 300 nm. As compared to the case without an IZO layer, under an injection current of 60–1000 mA, a 39–90% improvement in Lop has been achieved from LEDs (1.5 mm×1.5 mm) with a 300-nm-thick IZO TCL.
Growth, Fabrication, and Operating Characteristics of Ultra-Low Threshold Current Density 1.3 µm Quantum Dot Lasers
Authors: Ray Sumon K. , Groom Kristian M. , Hogg Richard A. , Liu Hui-Yun , Sellers Ian R. , Hopkinson Mark , Badcock Tom J. , Ramsay Andrew J. , Mowbray David J. , Skolnick Maurice S.
Published: July 2005

A detailed study of the operating characteristics of low threshold current density 1.3 µm quantum dot lasers is reported. The effects of gain saturation are discussed and the temperature performance of these devices is shown to be enhanced by the implementation of improved laser fabrication technologies.
Open-Circuit Voltage Improvement in InGaAs/InP Heterojunction Solar Cells
Authors: Kim Choul-Young , Cha Jung-Ho , Kim Jaeho , Kwon Young-Se
Published: July 2005

We proposed single-heterojunction and double-heterojunction cell structures to increase the open-circuit voltage in InGaAs/InP-based solar cells. Compared with a homojunction cell, an open-circuit voltage improvement for the single-heterojunction cell is not observed, but an increase of 30.2% in open-circuit voltage for the double hetero-junction cell is observed. As a result, the efficiency of the double-heterojunction cell is increased by 23.9% that of the homojunction cell.
Improvement in Extraction Efficiency of GaN-Based Light-Emitting Diodes with Textured Surface Layer by Natural Lithography
Authors: Yang Chiao-Chih , Horng Ray-Hua , Lee Chia-En , Lin Wen-Yu , Pan Kuan-Fu , Su Ying-Yong , Wuu Dong-Sing
Published: July 2005

In this study, p-side-up GaN-based light-emitting diodes (LEDs) with textured indium-tin oxide (ITO) or silicon dioxide (SiO2) surface layers were investigated by natural lithography using polystyrene spheres (PSs) as an etching mask. It was found that the ITO top layer provides better roughness than SiO2. Under the optimum surface treatment parameter, the roughnesses of textured ITO and SiO2 surface layers are 140 nm and 15 nm, respectively. The diameter of PSs in the textured ITO surface is still maintained at about 250–300 nm. Correspondingly, the size of PSs in the SiO2 surface is reduced to about 100 nm. The output powers of LEDs with textured ITO and SiO2 surfaces and conventional LEDs are 10.9, 9.5, and 8.5 mW at 20 mA, respectively. LEDs fabricated using the textured ITO surface produced an output power that exceeded that of planar-surface LEDs by about 28% at 20 mA dc current.
Optical Polarization Properties of InAs/GaAs Quantum Dot Semiconductor Optical Amplifier
Authors: Jayavel Pachamuthu , Kita Takashi , Wada Osamu , Ebe Hiroji , Sugawara Mitsuru , Arakawa Yasuhiko , Nakata Yoshiaki , Akiyama Tomoyuki
Published: July 2005

We have investigated cleaved-edge photoluminescence (PL) polarization properties of InAs/GaAs quantum dot (QD) traveling-type semiconductor optical amplifiers (SOAs). Transverse-electric (TE) and transverse magnetic (TM) mode PL intensities of the devices have been examined. TE-mode PL intensity of QD-SOA is observed to be much stronger than TM-mode. The results indicate that the valence band edge of the QDs is heavy-hole like. Temperature dependence on the PL polarization properties of QD-SOA has been carried out and analyzed. It is observed that an enhancement of TM-mode PL intensity of QD-SOA at higher temperature is due to the fact that the inhomogeneous thermal strain induced effect.
Photonic Crystal Slabs with Hexagonal Optical Atoms and Their Application in Waveguides
Authors: Yang Lin , Motohisa Junichi , Fukui Takashi
Published: July 2005

The standard plane wave expansion (PWE) method with the supercell method was used to calculate the band diagrams of photonic crystal slabs (PCSs) with hexagonal optical atoms. A hole-type PCS with hexagonal optical atoms has almost the same width of first band gap for the TE-like mode as its two-dimensional (2D) counterpart. However, the first band gap of a pillar-type PCS with hexagonal optical atoms shrinks considerably compared with that of its 2D counterpart. The hole-type PCS with normal hexagonal optical atoms has a slightly wider first band gap for TE-like modes than does that with orthogonal hexagonal optical atoms. PCSs with normal and orthogonal hexagonal optical atoms have band gaps that can be compared to those of PCSs with circular optical atoms. Hence they are appropriate structures for fabricating PC devices. The dispersion curves of line-defect PC waveguides were also calculated by the PWE method with the supercell method and several potential methods for modulating their dispersion curves were also discussed. Modulating the width of the line defect and the size of the optical atoms along the line defect were proved to be effective ways for obtaining a single-mode line-defect PC waveguide with a large bandwidth.
Optical Characteristics of Responsivity-Enhanced InGaAs/InP Heterojunction Phototransistors
Authors: Jo Young-Chang , Joe Seuk-Jin , Kim Hoon , Choi Pyong
Published: July 2005

A highly sensitive InGaAs/InP heterojunction phototransistor (HPT) has been proposed and characterized using front-side optical injection. We also present optimized epitaxial structures to increase the optical gain and discuss the device operation mechanism and experimental results. The experimental results show that our device has an optical responsivity of 122.5 A/W, which is significantly higher than that of a conventional PIN photodetector with the same light absorbing area. This optical responsivity is extremely high and seems to exceed that of the APD. This high value of responsivity originates from the optical gain-enhanced device structure. The typical optical gain is approximately 188, which is much higher than that of any HPTs that have been reported. This means HPTs are 188 times more sensitive than PIN photodetectors. The proposed device can be easily fabricated using conventional HBT processing without additional steps. With these InGaAs/InP HPTs, we can construct a highly sensitive near-IR imaging system to detect very weak optical signals.
Electrical Conduction Behavior of Layered Perovskite La1-xBa1+xGaO4-δ
Authors: Lee Kyu Hyoung , Kim Jong Hwa , Kim Hye Lim , Kim Shin , Lee Hong Lim
Published: July 2005

Layered perovskite oxides of the system La1-x
Ba1+x
GaO4-δ were synthesized and their electrical conduction behavior was studied. The oxides of the composition range 0≤x≤0.2 were analyzed as a single orthorhombic phase with a K2NiF4-type structure. In the presence of water vapor, proton conduction was observed due to the incorporation of water into the oxygen vacancies for these oxides. Below 350°C, La0.8Ba1.2GaO3.9 was considered to be a pure proton conductor and the activation energy for proton conduction was measured as 0.77 eV. In a dry atmosphere, it exhibited mixed conduction consisting of oxygen ions and holes at a high oxygen partial pressure, p(O2), and showed only oxygen-ion conduction at an intermediate and low p(O2).
Novel Cyclo Olefin Copolymer Used as Waveguide Film
Authors: Hwang Shug-June , Yu Hsin Her
Published: July 2005

A novel cyclo olefin copolymer (COC) waveguide film was fabricated and characterized. The optical properties as well as the absorption spectrum of this polymer film were observed using a prism coupler and by Fourier transformation infra-red (FTIR) spectroscopy. Atomic force microscopy (AFM) was also used to monitor the morphology of the waveguide film to probe the influence of an external electric field. In addition, the moisture resistance of this waveguide film was explored by water permeation measurements.
InGaAs/AlGaAs Quantum Wire DFB Buried HeteroStructure Laser Diode by One-Time Selective MOCVD on Ridge Substrate
Authors: Takasuka Yasuyuki , Yonei Kenji , Yamauchi Hiromi , Ogura Mutsuo
Published: July 2005

A quasi-buried heterostructure (BH) quantum wire (QWR)-distributed feedback (DFB) laser was realized by one-time selective metalorganic chemical vapor deposition (MOCVD) on a ridge substrate with a submicron grating. One-time selective MOCVD led to the formation of a ridge waveguide with a BH structure and a QWR array for gain-guided DFB laser diode (LD) without additional etching or regrowth process. The threshold current is 15 mA, and the threshold current density is 850 A/cm2. A stable single longitudinal mode was preserved until 3 Ith, after which another mode emerged at a high drive current at 813.6 nm. This suggests a complex-coupled DFB-mode operation. The elimination of the regrowth step enlarges the range of material for extended wavelengths and operational temperatures.
10 Gbps InGaAs:Sb-GaAs-GaAsP Quantum Well Vertical Cavity Surface Emitting Lasers with 1.27 µm Emission Wavelengths
Authors: Chang Ya-Hsien , Kuo Hao-Chung , Chang Yi-An , Chu Jung-Tang , Tsai Min-Ying , Wang Shing-Chung
Published: July 2005

InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) with 1.27 µm emission wavelength were grown by metal-organic chemical vapor deposition (MOCVD) and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than ∼35% as the temperature is increased from room temperature to 70°C. With a bias current of only 5 mA, the 3 dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10 Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with a modulation current efficiency factor (MCEF) of ∼5.25 GHz/(mA)1/2. Bit error rates of less than 10-12 are demonstrated for 10 Gb/s data transmission from 25°C to 70°C. We also accumulated life test data up to 1000 h at 70°C/10 mA.
Annealing Temperature Effects on Synthesis of n-TiO2/dye/p-CuI Solid-State Solar Cells
Authors: Rusop Mohamad , Shirata Tetsuya , Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: July 2005

The effects of annealing temperature on the properties of titanium dioxide (TiO2) films for the fabrication of dye-sensitized solid-state photovoltaic solar cells using XeCl excimer pulsed laser-deposited copper iodide (CuI) thin films, n-TiO2|dye|p-CuI cells have been studied. An efficient enhancement of incident photon-to-current conversion efficiency (IPCE) charge generation is observed by illumination through the TiO2 layer of the fabricated n-TiO2|dye|p-CuI cells. Dye molecules adsorbed on the TiO2 surface act as a relay, particularly under illumination through the TiO2 layer in the wavelength range of 300–400 nm. The cell performances are shown by in the current–voltage (I–V) working curves under illumination when exposed to AM 1.5 illumination condition (100 mW/cm2, 25°C). The n-TiO2|dye|p-CuI solid-state photovoltaic solar cell fabricated using TiO2 films annealed at 450°C for 6 h shows maximum short circuit current density (J
sc) of approximately 12.2 mA/cm2 and an open circuit voltage (V
oc) of approximately 480 mV with good reproducibility. The fill factor and power conversion efficiency were about 47.8% and 2.8%, respectively.
Design of Photonic Crystal Directional Coupler with High Extinction Ratio and Small Coupling Length
Authors: Yamamoto Noritsugu , Watanabe Yoshinori , Komori Kazuhiro
Published: July 2005

As one of the key component of photonic crystal optical circuit devices, the directional coupler is investigated. We explain the reason the directional coupler consisting of an ordinary symmetric parallel waveguide cannot have a high extinction ratio and a small coupling length simultaneously. To realize both characteristics simultaneously, we propose a novel directional coupler structure. By numerical calculation, we show the possibility of a directional coupler with a high extinction ratio (-24 dB) and a small coupling length (18a).
Sintering and Piezoelectric Properties of Potassium Sodium Niobate Ceramics with Newly Developed Sintering Aid
Authors: Matsubara Masato , Yamaguchi Toshiaki , Kikuta Koichi , Hirano Shin-ichi
Published: July 2005

As a candidate for lead-free piezoelectric materials, (K0.5Na0.5)NbO3 (KNN)-based ceramics have been successfully synthesized via a solid state reaction. In this study, KNN-based ceramics were sintered under atmospheric pressure by adding the newly developed sintering aid (K5.4Cu1.3Ta10O29, KCT). The effects of KCT addition on the sinterability and electrical properties of the KNN ceramics were examined. The KCT addition to KNN at more than 0.38 mol% was effective to improve the sinterability of the KNN ceramics. The phase transition temperature of the KNN ceramics prepared indicated that part of KCT reacted with the KNN matrix during the sintering process. The ε
r, k
p, N
p and Q
m values of prepared KNN ceramics strongly depended upon the KCT content. The KCT addition to KNN greatly improved the Q
m values (>1000) of the KNN ceramics. The Q
m and k
p of 0.38 mol% KCT added KNN ceramics were 1200 and 0.42, respectively. In addition, the KNN ceramics with 0.38 mol% KCT showed large field induced strain of 0.09% at 40 kV/cm, and d
33 of approximately 190 pm/V under a unipolar field from 30 to 40 kV/cm.
Carrier Transport Model for Lateral p-i-n Photodiode in High-Frequency Operation
Authors: Konno Kohkichi , Matsushima Osamu , Hara Kiyohito , Suzuki Gaku , Navarro Dondee , Miura-Mattausch Mitiko
Published: July 2005

We present an analytical model for carrier transport in a lateral p-i-n photodiode from DC to high-frequency operation. The model derives a nonstationary description of photodiode behavior in Fourier space. Transient photodiode response calculated by the model is in excellent agreement with measurement at high-applied reverse bias. The model is particularly useful for circuit simulation of optoelectronic integrated circuits where computational accuracy and reduced computational runtime are required.
Charge-State Control of Phosphorus Donors in Silicon-on-Insulator Metal-Oxide-Semiconductor Field-Effect Transistor
Authors: Ono Yukinori , Nishiguchi Katsuhiko , Inokawa Hiroshi , Horiguchi Seiji , Takahashi Yasuo
Published: July 2005

The drain current vs gate-voltage characteristics of a phosphorus-doped n-channel silicon-on-insulator metal-oxide-semiconductor field-effect transistor have been investigated. It was shown that, by controlling the voltage to the substrate at 20 K, the charge states of phosphorus donors can be changed in a controlled manner. Most of the donors are neutralized for the substrate voltage of around 0 V, while a major portion of the donors is ionized for a positive or negative voltage. Such a change can be detected by monitoring the change in the threshold voltage of the transistor. This is an experimental demonstration of the systematic control and monitoring of donor charge states in silicon.
Spectrum of Plasma Oscillations in Slot Diode with Two-Dimensional Electron Channel
Authors: Satou Akira , Khmyrova Irina , Chaplik Alexander , Ryzhii Victor , Shur Michael
Published: July 2005

We strictly calculate the spectrum of plasma oscillations in a slot diode containing a two-dimensional electron channel with strip-like highly conducting contacts. The spectrum of plasma oscillations in a gated two-dimensional electron channel (without contacts) is calculated as well. We use the hydrodynamic electron transport model involving a two-dimensional Poisson equation. It is shown that the features of the structure geometry affect the oscillation spectrum.
Quantum Dots and Their Tunnel Barrier in Semiconducting Single-Wall Carbon Nanotubes with a p-Type Behavior
Authors: Tsuya Daiju , Suzuki Masaki , Aoyagi Yoshinobu , Ishibashi Koji
Published: July 2005

Electrical transport properties have been measured in an individual p-type semiconducting single-wall carbon nanotube at the temperature range from 1.5 K to 160 K. The quantum dot transport has been observed, which depends on the gate voltage range. In the small positive gate voltage range, the single quantum dot behavior was observed, while the multi-dot behavior was observed in the further positive gate voltage. In the sufficiently large positive gate voltage range, no current flowed. The barrier height in the single quantum dot regime was estimated to be ∼10 meV by measuring the temperature dependence of the current–voltage curve at a Coulomb peak position.