Chew Beng Soh

Chew Beng Soh
Singapore Institute of Technology (SIT) | SIT · Electrical Engineering

ECE NUS (PhD)

About

69
Publications
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Introduction
Chew Beng Soh is currently a faculty of Singapore Institute of Technology (SIT), Engineering Cluster. Chew Beng does research in Condensed Matter Physics, and Solid State Physics, Surface Engineering and Composite materials

Publications

Publications (69)
Article
This paper reports the 3D printing of fibre-reinforced ceramic composite with hierarchical structures. Through printing precursor formulation, short SiC fibres have been successfully incorporated into silicate materials and gradient porous hierarchical structure has been achieved for the printed parts. The mechanical testing shows a 27% improvement...
Article
This article proposes a method for optimal placement of phasor measurement units (PMUs) to improve measurement redundancy distribution in a system under normal operating condition or in presence of contingency. The minimum number of PMUs is determined using integer linear programming method, after which the measurement redundancy is optimized using...
Article
Full-text available
Herrigbone structures are identified on the chitins of the Mantis shrimp. Bio-inspired helicoidal arrangement of composite layers can mimic these herringbone structures. First, the carbon composite samples are fabricated using the hand lay-up method, followed by a curing process using a hot press system. The impact absorption properties of these sa...
Article
Full-text available
Hip fractures has been prevalent especially among aged elderly. This can lead to permanent disability of the elderly as they are wheel-chaired bound after suffering from hip fractures. In this work, we explore the design of a protective hip pad which encapsulate the hydrogel and fibres composite in a laminated sheet. The hydrogel was fabricated usi...
Conference Paper
Recently there has been extensive research to address the shortcomings of the widely used phosphor coated Light Emitting Diodes (LEDs) such as the slow recombination rate. In-situ Indium rich InGaN quantum dots (QD) was incorporated into multi-quantum wells (MQWs) to generate a broad emission spectrum. In this research, we aim to study the effect o...
Article
Full-text available
Alcohol sensing devices provide safety precautions against exposure to toxic gases in both indoor and outdoor environments. In this study, for comparison between TiO2 and BaTiO3 materials, alcohol-sensing tests determine the better material. The two materials that makes up the seed layers have excellent dielectric constants while Titania nano-rods...
Article
InGaN/GaN multiple quantum well (MQW) structures have been grown by metalorganic chemical vapor deposition on c-plane sapphire substrates. Inverted diamond-like surface defects (i.e., V-pits) with a density of ∼5×109cm−2 have been observed in an eight-QW structure with Ga0.83In0.17N (3.6nm thick) and GaN (12.7nm thick) as the well- and barrier-mate...
Article
We report the fabrication and characterization of high voltage AlGaN/GaN metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) with selectively regrown In0.14Ga0.86N contact using a CMOS compatible gold-free process. Device with the regrown InGaN contact with a gate-to-drain spacing LGD of 5 µm achieves an off-state breakdown volt...
Article
High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the {111} facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ±...
Article
GaN grown on sapphire is electrochemically etched in HF and in KOH. Etching in HF results in a network of nanopillars while that etched in KOH results in a network of pores. The higher density of voids from the network of pores shows the highest strain relaxation for a 1.2 µm thick GaN overgrown on the porous templates. In general, a light-emitting...
Article
Auger recombination in InN films grown by metal-organic chemical vapor deposition was studied by steady-state photoluminescence at different laser excitation powers and sample temperatures. It was dominant over radiative recombination and Shockley-Read-Hall recombination at low temperatures, contributing to the sub-linear relationship between the i...
Article
We have investigated the microstructure and optical properties of GaN grown on vertically standing Si nanostructures by MOCVD. The array of Si nanostructures was formed by a simple metal-assisted etching of Si(111) substrates. The resulting nanostructures have size features ranging from 20 to 70 nm with fill-factor between 40-45%, and varying heigh...
Article
indium rich InGaN nanostructures grown by MOCVD were incorporated in InGaN/GaN quantum wells for long wavelength emission by optimizing the growth condition for the quantum dots (QDs) and InGaN quantum wells. The indium rich InGaN QDs were about 20 nm in diameter and 1.5 nm in height with a density of ∼1 × 1010 cm−2. The InGaN nanostructures in qua...
Article
Phosphor-free amber light emitting quantum dots with bimodal size distribution have been effectively incorporated in InGaN/GaN light emitting diodes (LEDs). With overgrowth of the LEDs structure on electrochemically etched nanoporous GaN templates, a reduction in density of threading dislocations and lower biaxial stress are achieved. A higher dens...
Article
Using temperature-dependent photoluminescence (PL), we report a detailed study on the optical transitions in AlyInxGa1−x−yN (0.01≤ × ≤ 0.023, 0.07 ≤ y ≤ 0.14) of variable thickness (20 – 100 nm) grown on GaN by metalorganic chemical vapor deposition (MOCVD). At 100 K, highest electron mobility has been obtained for samples with 40 nm thick AlInGaN...
Article
Indium rich InGaN nanostructures grown by metalorganic chemical vapor deposition were incorporated in InGaN/GaN quantum wells for long wavelength generation. These results were achieved by optimizing the growth temperature of the nanostructures, InGaN quantum well, the AlN capping layer and the GaN barrier layers. Before the growth of nanostructure...
Article
Full-text available
Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on na...
Article
Blue light emitting diodes (LEDs) have been fabricated with InGaN/GaN well layers (QWs) on micro-patterned sapphire substrate (PSS). Low pressure growth of GaN layer on PSS effectively reduces the density of edge dislocations. The growth of InGaN/GaN MQWs on PSS as compared to conventional sapphire substrate (CSS) improves the internal quantum effi...
Article
Phosphor-free apple-white light emitting diodes (LEDs) have been fabricated using dual stacked InGaN/GaN multiple quantum wells (MQWs) comprising a lower set of long wavelength emitting indium rich nanostructures incorporated in MQWs with an upper set of cyan-green emitting MQWs. The LEDs were grown on nano-epitaxial lateral overgrown (ELO) GaN tem...
Article
In this study, we report on the enhancement in the light extraction efficiency of GaN blue LEDs topped with ZnO nanorods. The ZnO nanorods were grown by a two-step hydrothermal synthesis with pre-coated ZnO nanoparticles under optimized condition to give the appropriate size and quality, giving an increase in the light output efficiency of 66%. Thi...
Article
We investigated the optical properties of ZnO nanorods on nanosilicon-on-insulator using variable temperature photoluminescence (PL) spectroscopy, and explored the contribution of exciton–phonon coupling and surface resonance effect on the emission characteristics of the nanorods. The low-temperature (<100 K) PL spectra revealed different strengths...
Article
Regrowth of GaN buffer layer on nanoporous GaN at different chamber temperature of 750 °C, 850 °C and 1000 °C are used to study the mechanism behind threading dislocations reduction in the GaN film subsequently overgrown. The growth of a 100 nm GaN buffer layer at 850 °C causes dislocations to bend into the underlying GaN and annihilated at the int...
Article
We have demonstrated deep green InGaN/GaN light emitting diodes (LEDs) on 100 nm thick (111)-oriented silicon-on-insulator (SOI) substrate. The LED structures are grown by metalorganic chemical vapour deposition. High-resolution X-ray diffraction and transmission electron microscopy have been used to characterize the structural quality of the LED l...
Article
Phosphor free tunable white light emitting diodes (LEDs) have been fabricated using stacked InGaN/GaN quantum wells (QWs) comprised of a lower set of red emitting QWs with an upper set of blue and green emitting QW layers. With antisurfactant treatment, indium rich InGaN nanostructures are incorporated in the InGaN/GaN quantum well during growth. A...
Article
The authors have employed variable temperature photoluminescence (PL) and time-resolved PL spectroscopy to probe the exciton recombination in high density and vertically aligned ZnO nanorods grown on p-type GaN/sapphire template. The low-temperature PL characterizes the dominant near-band-edge excitonic emissions from such nanorod arrays. At 4.3 K,...
Article
Full-text available
Low defect density GaN was achieved through dislocation annihilation by regrowing GaN on strain relaxed nanoporous GaN template formed by UV-enhanced electrochemical etching. The InGaN/GaN single and multiple quantum wells grown on this nanoporous GaN template show enhanced indium incorporation due to strain relaxation. The step edges of regrown Ga...
Article
We report on the fabrication of a nano-cone structured p-GaN surface for enhanced light extraction from tunable wavelength light emitting diodes (LEDs). Prior to p-contact metallization, self-assembled colloidal particles are deposited and used as a mask for plasma etching to create nano-cone structures on the p-GaN layer of LEDs. A well-defined pe...
Article
Phosphor-free cool white emitting light emitting diodes (LEDs) have been fabricated using a dual stacked In Ga N / Ga N multiple quantum wells (MQWs) comprising of a lower set of MQWs emitting yellow and an upper set of MQWs emitting blue. The lower set of MQWs incorporates indium-rich InGaN connected-dot nanostructures with a height of ∼1.0 nm in...
Article
Commercial GaN based white LEDs have been fabricated using phosphor coating of blue LEDs. We report on the growth of InGaN/GaN based white LEDs using In-rich InGaN quantum dots incorporated in the MQW layers. The photoluminescence spectrum of the MQWs shows a broad emission spectrum covering 400 to 700 nm. Cross-section TEM shows the existence of p...
Article
We report on the growth and fabrication of a LED which emits light, tunable in color, as the injection current is increased from I = 1.0 mA to 40 mA. Two multiple quantum well (MQWs) structures, designated as A and B, are grown in the LEDs, with quantum dots embedded in MQWs B while MQWs A are conventional blue emitting quantum well layers. A broad...
Article
Implantation of erbium (Er) into GaN is useful in creating selected areas to emit at the green, yellow and infrared wavelengths. Enhanced erbium activation is obtained when erbium is implanted into porous GaN formed by electrochemical etching than into as-grown GaN. This is due to the increase in surface areas for light extraction and the availabil...
Article
The high density of threading dislocations, often leading to the formation of inverted hexagonal pits in InGaN/GaN heterostructures on sapphire substrates, lowers the radiative efficiency of light emitting devices. In this study, a cracked AlGaN template has been implemented as a strain-relaxed layer for subsequent growth of InGaN/GaN heterostructu...
Article
The introduction of Si burst during the growth of GaN film on Si(111) substrate by MOCVD formed a Six Ny layer which leads to an effective reduction in the density of screw dislocations. The reduction is associated with bending of screw dislocations to form a square dislocation loop when neighbouring dislocations with opposite Burger's vector paire...
Article
In this article, we report on the structural and optical properties of ZnO nanorods grown at a relatively low temperature on glass substrates with and without a ZnO buffer by metallorganic chemical vapor deposition for transparent optoelectronic application. The thickness of the buffer layer strongly influences the aspect ratio and alignment of the...
Article
Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nano-scale pores of size 20-50 nm in the underlying grains. Electrochemical etching at The effect of GaN buffer layer grown at various temperatures from 650°C to 1015°C on these as-fabricated nano-pores templates are investigated by transmission elect...
Article
High density porous has been fabricated by UV-enhanced electrochemical etching on Si-doped layer grown by metallorganic chemical vapor deposition. A redshift from 0.7 to in the (high) phonon peak of was observed in this porous with respect to as-grown . As the phonon peak of a stress-free is observed at , it means that the fabrica...
Article
The epitaxy growth of InGaN/GaN MQWs posed a great challenge, especially when high In content have to be incorporated for long wavelength applications such as the cyan and green LEDs. To realize devices with superior characteristic, In-rich InGaN nanostrucutres (QDs) have been fabricated using InGaN wetting layer and trimethylIndium treatment in In...
Article
Porous GaN subjected to heat treatment under in-situ MOCVD chamber annealing at 850 °C for 3 minutes has shown significant annihilation of threading dislocations and improvement of its optical quality. Similar phenomenon is not observed for the porous GaN samples annealed at lower temperatures. The annealing was done in a mixed of N2 and NH3 ambien...
Article
A simple and cost-effective Si-doped porous GaN is fabricated by UV-enhanced electrochemical etching. An optimum current density of 20 mA/cm² applied for an hour in dilute NaOH solution produces a high density of uniform pores. Cross-section TEM reveals that etching takes place along the (0001) direction. A red shift of 0.7 cm⁻¹ in the E₂(high) pho...
Article
Growth of gallium nitride (GaN) on strain relaxed nanoporous GaN template by metal-organic chemical vapor deposition has produced GaN layer with 60% reduction in threading dislocation density (TDD). The porous GaN was annealed at 850 °C for 3 min in a mixed of nitrogen and ammonia ambient, which annihilated most TDs within the porous region via air...
Article
In the growth of InGaN multiple quantum well structure, V-pits has been observed to be initiated at the threading dislocations which propagate to the quantum well layers with high indium composition and substantially thick InGaN well. A set of samples with varying indium well thickness (3–7.6 nm) and composition (10–30%) are grown and characterized...
Article
Deep level transient spectroscopy has been used to characterize the deep levels in InGaN/GaN grown on sapphire substrate as well as on free-standing GaN. The deep levels at Ec−Et∼0.17–0.23 eV and Ec−Et∼0.58–0.62 eV have been detected in our samples which are present in GaN samples reported by others. These two deep levels have been attributed by us...
Article
Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20–50 nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650 to 1015 ° C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer lay...
Article
A process methodology has been adopted to bond GaN thin films to Si(100) substrates using the combination of laser lift-off and direct wafer fusion. Using optimum excimer laser conditions, 2–10 μm of GaN is lifted-off from sapphire. The lifted-off thin film is cleared from gallium residual and then suitably treated in a hydrofluoric, nitric and ace...
Article
We report a micro-Raman study of ordered self-organized dot patterns on silicon surface realized by low-energy Ar+-ion irradiation. Atomic force microscopy reveals that the average size of the silicon nanodots on the surface varies in the range 50–60nm with an average height of about 12–13nm. A gradual increase in downward shift and asymmetric broa...
Article
The effects of 248 nm KrF excimer laser irradiation on the properties of Mg-doped GaN film were investigated. The laser irradiation-induced property changes were studied by photoluminescence, I- V, C- V, DLTS, AFM measurements. It was found that under appropriate laser conditions, 248 nm KrF excimer laser irradiation could significantly increase th...
Article
The piezoelectric field generated at the AlyInxGa1−x−yN/GaN interface creates a two-dimensional electron gas (2DEG). The maximum 2DEG mobility in AlyInxGa1−x−yN/GaN, for a nominal composition of x = 0.01 and y = 0.07, is obtained for the 40-nm-thick quaternary epilayer. With further increase in the AlyInxGa1−x−yN thickness, the mobility drops due t...
Article
Using temperature-dependent photoluminescence (PL) measurements, we report a comprehensive study on optical transitions in AlyInxGa1-x-yN epilayer with target composition, x=0.01 and y=0.07 and varying epilayer thickness of 40, 65 and 100 nm. In these quaternary alloys, we have observed an anomalous PL temperature dependence such as an S-shape band...
Article
Full-text available
In a certain growth mode, V pits have been observed in AlyInxGa1−x−yN grown by metal–organic chemical vapour deposition. Room temperature photoluminescence (PL) spectra from these quaternary alloys show strong band-to-band emission with equally intense yellow luminescence (YL). Simultaneous measurements of the PL intensity and topography using ult...
Article
To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-dope...
Article
The AlInGaN alloy has emerged as the material for potential use in UV light emitting diodes and lasers due to its higher emission quantum efficiency. However, surface defects like hexagonal pits appear on the surface of this quaternary alloy and formation of these pits can degrade the device performance. In this study, we have observed inverted hex...
Article
Two sets of AlInGaN quaternary epilayers grown by metal organic chemical vapor deposition (MOCVD) were studied by atomic force microscopy (AFM), high-resolution X-ray diffraction (HR-XRD) and photoluminescence (PL) spectroscopy. In all samples a large number of pits have been observed on the surface with the density of 1×109cm−2, and hexagonal open...
Article
The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ~18, ~35, and ~70 meV, which are respectively associated with the Si shallow donors, O impuriti...
Article
In this paper, deep level defects in high quality continuous GaN films grown over a cracked Si-doped GaN template has been studied using digital deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). From TEM observation, it is found that the density of pure screw dislocations have been effectively suppressed while pur...
Article
In this paper, deep level defects in undoped and Si-doped GaN have been studied using digital deep level transient spectroscopy. Common trap levels at Ec -ET ∼ 0.15-0.20 eV and 0.59-0.62 eV were detected for both undoped and Si-doped samples. For the doped samples, three additional defect levels at Lc-Et ∼ 0.11, 0.28, and 0.45 eV were detected. The...
Article
Deep levels in InGaAlP films grown using two different V/III ratios have been studied by employing deep level transient spectroscopy (DLTS). The two samples investigated have the same composition of (Al0.3Ga0.7)0.51In0.49P and a film thickness of 0.6μm, but grown with V/III ratios 75 and 50. Two defect levels with activation energies 0.23 and 0.78e...
Article
Deep level defects in both p+/n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at Ec−Et=0.23–0.27eV with a capture cross-section of the order of 10−19–10−16cm2 for both the p+/n and n-type Schottky GaN diodes. For one se...
Article
Deep level transient spectroscopy (DLTS) characterization of defects in InGaAlP films grown using two different V/III ratios was carried out. Electron trap levels with activation energies of 0.42 eV and 0.78 eV were detected in the sample with V/III ratio of 50 and 75 respectively, using isothermal DLTS. In this paper, the severe temperature depend...
Article
In this paper, the deep level defects in (pi)-GaN Schottky and the p/(pi)GaN diodes have been studied using digital deep level transient spectroscopy (DLTS). The alternative isothermal technique offered by the DL8000 system is used in complement to conventional temperature scan technique. Electron trap levels at Ec -Et ~ (0.23 - 0.27 eV) are detect...

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