Browsing by Author "Dee, Chang Fu"

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AlGaN/GaN MIS-HEMTs With High Quality ALD-Al2O3 Gate Dielectric Using Water and Remote Oxygen Plasma As Oxidants
(2018-12-01)
Wang, Huan-Chung
;
Hsieh, Ting-En
;
Lin, Yueh-Chin
;
Luc, Quang Ho
;
Liu, Shih-Chien
We demonstrate the electrical performances of AlGaN/GaN metal-insulator-semiconductor-high electron mobility transistors (MIS-HEMTs) with high quality Al2O3 gate dielectric deposited by plasma enhanced atomic layer deposition using both H2O and remote O-2 plasma as oxygen sources. Excellent gate-dielectric/GaN interface and Al2O3 film quality were obtained, resulting in a very small threshold voltage hysteresis and a low interface trap density. The MIS-HEMT device exhibited high on/off current ratio of similar to 10(10), steep subthreshold slope, small gate leakage current, low dynamic on-resistance degradation, and effectively current collapse suppression. These results indicate that incorporating remote O-2 plasma in the ALD-Al2O3 deposition process is an effective and simple way to provide high quality gate dielectric for the GaN MIS-HEMTs production.
Characterization of AlInN Layer Grown on GaN/Sapphire Substrate by MOCVD
(2013-02-01)
Huang, Wei-Ching
;
Chang, Edward-Yi
;
Wong, Yuen-Yee
;
Lin, Kung-Liang
;
Hsiao, Yu-Lin
The AlInN layers have been grown with different growth parameters on GaN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The effects of growth parameters such as pressure and temperature on the Al incorporation during AlInN material growth have been investigated. The results showed that lower pressure provides a tendency for higher Al incorporating in the AlInN layer. Besides, as the temperature was increased from 700 degrees C to 780 degrees C, an estimation of 4% reduction on the indium composition has been observed for each 20 degrees C increment. XRD analysis showed that the best crystal quality of AlInN occured at 80% Al composition because of the higher lattice matching with GaN. Based on the above criteria, an Al0.8In0.2N/GaN HEMT device with 2 mu m gate length has also been fabricated. The DC characteristics showed a saturated current, I-dss of 280 mA/mm and transconductance of 140 mS/mm.
Effect of Graded AlxGa1-xN Layers on the Properties of GaN Grown on Patterned Si Substrates
(2012-02-01)
Hsiao, Yu-Lin
;
Lu, Lung-Chi
;
Wu, Chia-Hsun
;
Chang, Edward Yi
;
Kuo, Chien-I
2.2-mu m-thick crack-free GaN films were grown on patterned Si substrates. The crack-free GaN films were obtained by patterning Si substrate and optimizing the graded AlxGa1-xN layers. With the increase of the graded AlxGa1-xN layer thickness, the GaN crystal quality improved as judged from the X-ray diffraction data. By applying multi-AlxGa1-xN layers on the patterned Si substrate, a 31% reduction of tensile stress for the GaN film was obtained as measured by micro-Raman. For the AlGaN/GaN high electron mobility transistor grown on 1 x 1 cm(2) larger patterns, the device exhibits maximum drain current density of 776 mA/mm and maximum transconductance of 101 mS/mm. (c) 2012 The Japan Society of Applied Physics
Effect of surface passivation by a low pressure and temperature environment-grown thermal oxide layer for multi-crystalline silicon solar cells
(2018-08-30)
Liao, Shun Sing
;
Chuang, Chuan Lung
;
Lin, Yueh Chin
;
Dee, Chang Fu
;
Majlis, Burhanuddin Yeop
In this study, we show that the efficiency and carrier life time of multi-crystalline silicon solar cells were significantly improved by using a low pressure (20,000 Pa) and temperature (650 degrees C similar to 750 degrees C) environment grown thermal oxide (TO) as the surface passivation layer. In this experiment, during the first stage, the oxidation process was done at 650 degrees C and a lower pressure of 20,000 Pa for 2 mins under the flow a gas mixture of N-2/O-2 in ratio of 2:1. In the second stage, a temperature of 750 degrees C was used at the same pressure for the post-growth annealing process under a pure N-2 ambient for 25 mins. Consequently, conversion efficiency was significantly increased by 0.55% with the surface passivation layer grown by low pressure and temperature TO process. The sheet resistance, carrier lifetime, internal quantum efficiency (IQE), increased by 6.32 Omega/sq., 22.18 mu s, 4.33%, respectively, and the average reflection was reduced of 0.62%. Thus, the low pressure and temperature thermal oxidation process was an efficient way to increase the efficiency of the multi-crystalline silicon solar cells.
Electrical bistabilities behaviour of all-solution-processed non-volatile memories based on graphene quantum dots embedded in graphene oxide layers
(2019-09-01)
Jaafar, Muhammad Musoddiq
;
Ooi, Poh Choon
;
Wee, M. F. Mohd. Razip
;
Haniff, Muhammad Aniq Shazni Mohammad
;
Mohamed, Mohd Ambri
This study demonstrates the feasibility of all-solution-processed mean to fabricate carbon-based non-volatile memory (NVM). The NVM devices were fabricated on polyethylene terephthalate (PET) substrate using spin-coating and spray-coating techniques in the structure of silver nanowires (AgNWs)/graphene oxide (GO)/graphene quantum dots (GQDs)/graphene oxide (GO)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/PET. PEDOT:PSS was used as the bottom conductive layer and deposited by spin-coating method. GQDs were used as a charge trapping site in the structure and embedded in the two GO insulator layers. The AgNW metal electrode was formed on top of GO/GQDs/GO/PEDOT:PSS by the spray-coating method. The overall smooth surface morphology of the spray-coated films serves as good contact with the top metal electrode. The electrical characterization of the fabricated device shows the bistable current states with the ON/OFF ratio of 10(5). The NVM device can be programmed and erased multiple times. Various conduction mechanisms were proposed to describe the charge trapping process in GQD based on the obtained current-voltage measurement.
Evaluation of AlGaN/GaN metal-oxide-semicondutor high-electron mobility transistors with plasma-enhanced atomic layer deposition HfO2/AlN date dielectric for RF power applications
(2017-09-01)
Chiu, Yu Sheng
;
Luc, Quang Ho
;
Lin, Yueh Chin
;
Huang, Jui Chien
;
Dee, Chang Fu
A plasma enhanced atomic layer deposition (PEALD) HfO2/AlN dielectric stack was used as the gate dielectric for AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) for high-frequency power device applications. The capacitance-voltage (C-V) curves of the HfO2/AlN/GaN MOS capacitor (MOSCAP) showed a small frequency dispersion along with a very small hysteresis (similar to 50 mV). Moreover, the interface trap density (D-it) was calculated to be 2.7 x 10(11)cm(-1)V(-1) s(-1) at 150 degrees C. Using PEALD-AlN as the interfacial passivation layer (IPL), the drain current of the HfO2/AlN MOS-HEMTs increased by about 46% and the gate leakage current decreased by six orders of magnitude as compared with those of the conventional Schottky gate AlGaN/GaN HEMTs processed using the same epitaxial wafer. The 0.3-mu m-gate-length HfO2/AlN/AlGaN/GaN MOS-HEMTs demonstrated a 2.88W/mm output power, a 23 dB power gain, a 30.2% power-added efficiency at 2.4 GHz, and an improved device linearity as compared with the conventional AlGaN/GaN HEMTs. The third-order intercept point at the output (OIP3) of the MOS-HEMTs was 28.4 as compared with that of 26.5 for the conventional GaN HEMTs. Overall, the MOS-HEMTs with a HfO2/AlN gate stack showed good potential for high-linearity RF power device applications. (C) 2017 The Japan Society of Applied Physics
High-frequency Sezawa guided mode of GaN/sapphire using high aspect ratio electrode
(2019-11-01)
Jaafar, Muhammad Musoddiq
;
Wee, M. F. Mohd Razip
;
Dee, Chang Fu
;
Faiz, Mohd Syafiq
;
Chang, Edward Yi
The propagation of surface acoustic wave (SAW) on the piezoelectric substrate requires conventionally an interdigitated electrode structure to excite the mechanical displacement at resonance frequency. The control of the electrode thickness could be useful to manipulate the energy confinement and the band dispersion of the surface guided mode. It has been demonstrated recently that high aspect ratio (HAR) electrode could produce a dispersive shear horizontal and vertically polarized surface modes in the bulk piezoelectric substrate. In this theoretical study, we propose to employ a high aspect ratio electrode on top of the GaN/sapphire-layered substrate enabling the presence of Sezawa surface mode. Based from the dispersion band, we obtained a higher frequency of surface guided mode in the non-radiative zone in the GaN/sapphire heterostructure configuration compared to the bulk GaN substrate. Indeed, these guided modes are induced by the hybridization between Sezawa surface mode and the mechanical resonance of the HAR electrode producing nearly a flat band at the limit of First Brillouin Zone. Furthermore, the displacement of each guided modes indicates the confinement of energy mostly in the electrode with a slight amount of energy in the top layer of the substrate. We demonstrated also the frequency tuning of guided mode using diverse materials for the electrode but also the thickness of GaN layer. The obtained results could be useful for the development of high-frequency telecommunication and sensing device based on Sezawa surface acoustic wave.
InGaP/GaAs Dual-Junction Solar Cell with AlGaAs/GaAs Tunnel Diode Grown on 10 degrees off Misoriented GaAs Substrate
(2012-08-01)
Yu, Hung Wei
;
Chung, Chen Chen
;
Wang, Chin Te
;
Hong Quan Nguyen
;
Binh Tinh Tran
InGaP/GaAs dual-junction solar cells with different tunnel diodes (TDs) grown on misoriented GaAs substrates are investigated. It is demonstrated that the solar cells with P++-AlGaAs/N++-GaAs TDs grown on 10 degrees off GaAs substrates not only show a higher external quantum efficiency (EQE) but also generate a higher peak current density (J(peak)) at higher concentration ratios (185 x) than the solar cells with P++-GaAs/N++-InGaP TDs grown on 6 degrees off GaAs substrates. Furthermore, the cell design with P++-AlGaAs/N++-GaAs TDs grown on 10 degrees off GaAs substrates does not generate a disordered InGaP epitaxial layer during material growth, and thus shows superior current-voltage characteristics. (c) 2012 The Japan Society of Applied Physics
Porous (001)-faceted Zn-doped anatase TiO2 nanowalls and their heterogeneous photocatalytic characterization
(2014-01-01)
Saad, Siti Khatijah Md
;
Umar, Akrajas Ali
;
Hong Quan Nguyen
;
Dee, Chang Fu
;
Salleh, Muhamad Mat
The synthesis of a poriferous and high energy (001) faceted anatase Zn-doped TiO2 nanowall (ZnTNW), vertically grown on an indium tin oxide substrate, is presented. The ZnTNW was prepared using a modified liquid phase deposition method using zinc nitrate (Zn(NO3)(2)center dot xH(2)O) as a fluoride scavenger in the presence of hexamethylenetetramine. In a typical procedure, the ZnTNW nanowall with length and thickness of approximately 2 mu m and 60 nm, respectively, can be obtained from the reaction during a 5 h growth process. X-ray diffraction analysis shows that the nanowall has an anatase structure with a dominant high energy (001) basal plane. Meanwhile, the X-ray energy dispersive analysis confirms the presence of Zn in the TiO2 nanowall. High resolution transmission electron microscopy analysis results reveal, surprisingly, that the ZnTNW is single crystalline in nature although it has a highly porous (surface and bulk) structure. Photocatalytic properties of the ZnTNW were examined in the degradation of methylene blue. It was found that the ZnTNW exhibits excellent photocatalytic efficiency with kinetic reaction rate, turnover number and turnover frequency as high as 0.004 min(-1), 760 and 11 min(-1), respectively. The photocatalytic performance of the ZnTW was found to be higher for about 10% and 50% than the pristine TiO2 nanowalls and (001) faceted poriferous TiO2 microtablet, which reflected the effective effect of the Zn doping. The ZnTNW may find potentially use in photocatalytic heterogeneous applications.
Reliability study of high-k La2O3/HfO2 and HfO2/La2O3 stacking layers on n-In0.53Ga0.47As metal-oxide-semiconductor capacitor
(2016-02)
Chu, Chung-Ming
;
Lin, Yueh-Chin
;
Lee, Wei-I
;
Dee, Chang Fu
;
Wong, Yuen-Yee
This study investigates the time-dependent dielectric breakdown (TDDB) characteristics of La2O3/HfO2 and HfO2/La2O3 stacking layers on an n-In0.53Ga0.47As metal-oxide-semiconductor capacitor. Both designs improved the reliability compared with a single layer of HfO2. The TDDB followed the thermochemical E model. The current transportation mechanism changed from thermionic emission to Frenkel-Poole emission because of the traps creation under voltage stress. Both designs resulted in similar lifespans and voltage accelerating factors. However, the La2O3/HfO2 design had a longer lifespan because of the lower interface trap density and insertion of the HfO2 diffusion barrier layer between La2O3 and n-In0.53Ga0.47As. The oxide stacks exhibited excellent reliability and achieved a lifespan of 28.4 years. (C) 2016 The Japan Society of Applied Physics
Structural and photoluminescence investigation on the hot-wire assisted plasma enhanced chemical vapor deposition growth silicon nanowires
(2012-06-01)
Chong, Su Kong
;
Goh, Boon Tong
;
Wong, Yuen-Yee
;
Nguyen, Hong-Quan
;
Do, Hien
High density of silicon nanowires (SiNWs) were synthesized by a hot-wire assisted plasma enhanced chemical vapor deposition technique. The structural and optical properties of the as-grown SiNWs prepared at different rf power of 40 and 80 W were analyzed in this study. The SiNWs prepared at rf power of 40 W exhibited highly crystalline structure with a high crystal volume fraction. X-C of similar to 82% and are surrounded by a thin layer of SiOx. The NWs show high absorption in the high energy region (E > 1.8 eV) and strong photoluminescence at 1.73 to 2.05 eV (red-orange region) with a weak shoulder at 1.65 to 1.73 eV (near IR region). An increase in rf power to 80 W reduced the X-C to similar to 65% and led to the formation of nanocrystalline Si structures with a crystallite size of < 4 nm within the SiNWs. These NWs are covered by a mixture of uncatalyzed amorphous Si layer. The SiNWs prepared at 80 W exhibited a high optical absorption ability above 99% in the broadband range between 220 and similar to 1500 nm and red emission between 1.65 and 1.95 eV. The interesting light absorption and photoluminescence properties from both SiNWs are discussed in the text. (C) 2012 Elsevier B.V. All rights reserved.
Structure deformation of indium oxide from nanoparticles into nanostructured polycrystalline films by in situ thermal radiation treatment
(2013-10-17)
Chong, Su Kong
;
Azizan, Siti Nur Azieani
;
Chan, Kee Wah
;
Hong-Quan Nguyen
;
Chiu, Wee Siong
A microstructure deformation of indium oxide (In2O3) nanoparticles by an in situ thermal radiation treatment in nitrous oxide plasma was investigated. The In2O3 nanoparticles were completely transformed into nanostructured In2O3 films upon 10 min of treatment time. The treated In2O3 nanoparticle sample showed improvement in crystallinity while maintaining a large surface area of nanostructure morphology. The direct transition optical absorption at higher photon energy and the electrical conductivity of the In2O3 nanoparticles were significantly enhanced by the treatment.
The Effect of the Thickness of the Low Temperature AlN Nucleation Layer on the Material Properties of GaN Grown on a Double-Step AlN Buffer Layer by the MOCVD Method
(2016-02)
Huang, Wei-Ching
;
Chu, Chung-Ming
;
Hsieh, Chi-Feng
;
Wong, Yuen-Yee
;
Chen, Kai-Wei
The influence of low-temperature AlN (LT-AlN) nucleation layer thickness on the material properties of the GaN layer grown on the double-step AlN layer is investigated. When GaN was grown without the LT-AlN nucleation layer, the GaN layer has low sheet resistance of 464 ohm/sq and the surface was decorated with pitted region. On the other hand, when a LT-AlN layer with a thickness of 5 nm was inserted, a GaN layer with sheet resistance higher than 10(6) ohm/sq was achieved. This thin nucleation layer also improved the GaN morphology, suppressed inversion domain formation, and reduced oxygen impurity incorporation. However, the surface morphology and quality of the GaN crystal were severely degraded when the LT-AlN thickness was increased to 10 nm due to the formation of disorientated grains in the LT-AlN layer.
The Growth and Fabrication of High-Performance In0.5Ga0.5As Metal-Oxide-Semiconductor Capacitor on GaAs Substrate by Metalorganic Chemical Vapor Deposition Method.
(2012-01-01)
Hong Quan Nguyen
;
Hai Dang Trinh
;
Yu, Hung Wei
;
Hsu, Ching Hsiang
;
Chung, Chen Chen
Growth conditions have investigated for growing high quality In0.3Ga0.7As and In0.5Ga0.5As on GaAs substrate by metalorganic chemical vapor deposition method. Annihilation reactions between threading dislocations observed by transmission electron microscopy are experimental evidences to confirm threading dislocations had been blocked in InxGa1-xAs buffer layers. A high quality smooth surface In0.5Ga0.5As epi-film with threading dislocation density of 2x10(6) cm(-2) was achieved at growth temperature of 490 degrees C. Metal-oxide-semiconductor capacitor devices fabricated on In0.5Ga0.5As/GaAs perform nice capacitance-voltage response, with small frequency dispersion. The conductance contours indicate that the Fermi level moves freely to the lower part of the InGaAs bandgap without pinning.
The growth of pine-leaf-like hierarchical SnO2 nanostructures
(2014-01-01)
Dee, Chang Fu
;
Tiong, Teck Yaw
;
Varghese, Binni
;
Sow, Chorng-Haur
;
Wong, Yuan-Yee
Pine-leaf-like SnO2 hierarchical nanostructures (NSs) were grown by a two-step vapour transport deposition process with a combination of vapour-solid and vapour-liquid-solid mechanisms at the primary and secondary processes, respectively. This type of hierarchical structure consisted of SnO2 trunk with homo-branching nanowires (NWs). The branched NWs connected the trunk NWs at included angles of 56 degrees and 90 degrees for two different types of hierarchical NSs. Based on the thermodynamic calculation, the formation of branched NWs at those angles are all energetically favourable.
The growth of pine-leaf-like hierarchical SnO2 nanostructures
(2014-01-01)
Dee, Chang Fu
;
Tiong, Teck Yaw
;
Varghese, Binni
;
Sow, Chorng-Haur
;
Wong, Yuan-Yee
Pine-leaf-like SnO2 hierarchical nanostructures (NSs) were grown by a two-step vapour transport deposition process with a combination of vapour-solid and vapour-liquid-solid mechanisms at the primary and secondary processes, respectively. This type of hierarchical structure consisted of SnO2 trunk with homo-branching nanowires (NWs). The branched NWs connected the trunk NWs at included angles of 56 degrees and 90 degrees for two different types of hierarchical NSs. Based on the thermodynamic calculation, the formation of branched NWs at those angles are all energetically favourable.
Titanium dioxide-mediated resistive nanobiosensor for E. coli O157:H7
(2020-03-17)
Nadzirah, Sh.
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Hashim, U.
;
Gopinath, Subash C. B.
;
Parmin, N. A.
;
Hamzah, Azrul Azlan
A titanium dioxide nanoparticle (TiO2 NP)-mediated resistive biosensor is described for the determination of DNA fragments of Escherichia coli O157:H7 (E. coli O157:H7). The sol-gel method was used to synthesize the TiO2 NP, and microlithography was applied to fabricate the interdigitated sensor electrodes. Conventional E. coli DNA detections are facing difficulties in long-preparation-and-detection-time (more than 3 days). Hence, electronic biosensor was introduced by measuring the current-voltage (I-V) DNA probe without amplification of DNA fragments. The detection scheme is based on the interaction between the electron flow on the sensor and the introduction of negative charges from DNA probe and target DNA. The biosensor has a sensitivity of 1.67 x 10(13) omega/M and a wide analytical range. The limit detection is down to 1 x 10(-11) M of DNA. The sensor possesses outstanding repeatability and reproducibility and is cabable to detect DNA within 15 min in a minute-volume sample (1 mu L).
Tunable Spectrum Selectivity for Multiphoton Absorption with Enhanced Visible Light Trapping in ZnO Nanorods
(2018-05-17)
Tan, Kok Hong
;
Lim, Fang Sheng
;
Toh, Alfred Zhen Yang
;
Zheng, Xia-Xi
;
Dee, Chang Fu
Observation of visible light trapping in zinc oxide (ZnO) nanorods (NRs) correlated to the optical and photoelectrochemical properties is reported. In this study, ZnO NR diameter and c-axis length respond primarily at two different regions, UV and visible light, respectively. ZnO NR diameter exhibits UV absorption where large ZnO NR diameter area increases light absorption ability leading to high efficient electron-hole pair separation. On the other hand, ZnO NR c-axis length has a dominant effect in visible light resulting from a multiphoton absorption mechanism due to light reflection and trapping behavior in the free space between adjacent ZnO NRs. Furthermore, oxygen vacancies and defects in ZnO NRs are associated with the broad visible emission band of different energy levels also highlighting the possibility of the multiphoton absorption mechanism. It is demonstrated that the minimum average of ZnO NR c-axis length must satisfy the linear regression model of Z(p,min) = 6.31d to initiate the multiphoton absorption mechanism under visible light. This work indicates the broadening of absorption spectrum from UV to visible light region by incorporating a controllable diameter and c-axis length on vertically aligned ZnO NRs, which is important in optimizing the design and functionality of electronic devices based on light absorption mechanism.