Vivian Kaixin Lin

AlGaN/GaN two-dimensional-electron gas heterostructures on 200 mm diameter Si(111)

This Letter reports on the epitaxial growth, characterization, and device characteristics of crack-free AlGaN/GaN heterostructures on a 200 mm diameter Si(111) substrate. The total nitride stack thickness of the sample grown by the metal-organic chemical vapor deposition technique is about 3.3 ± 0.1 μm. The structural and optical properties of these layers are studied by cross-sectional scanning transmission electron microscopy, high-resolution x-ray diffraction, photoluminescence, and micro-Raman spectroscopy techniques. The top AlGaN/GaN heterointerfaces reveal the formation of a two-dimensional electron gas with average Hall mobility values in the range of 1800 to 1900 cm2/Vs across such 200 mm diameter GaN on Si(111) samples. The fabricated 1.5 μm-gate AlGaN/GaN high-electron-mobility transistors exhibited the drain current density of 660 mA/mm and extrinsic transconductance of 210 mS/mm. These experimental results show immense potential of 200-mm diameter GaN-on-silicon technology for electronic devi...

Damping of the acoustic vibrations of individual gold nanoparticles.

In this letter, the ultrafast vibrational dynamics of individual gold nanorings has been investigated by femtosecond transient absorption spectroscopy. Two acoustic vibration modes have been detected and identified. The influence of the mechanical coupling at the nanoparticle/substrate interface on the acoustic vibrations of the nano-objects is discussed. Moreover, by changing the environment of the nanoring, we provide a clear evidence of the impact of the surrounding medium on the damping of the acoustic vibrations. Such results are reported here for the first time on individual nanoparticles. This work points out a new sensing method based on the sensitivity of the acoustic vibration damping to the surrounding medium.

Direct Current and Microwave Characteristics of Sub-micron AlGaN/GaN High-Electron-Mobility Transistors on 8-Inch Si(111) Substrate

We report for the first time the DC and microwave characteristics of sub-micron gate (~0.3 µm) AlGaN/GaN high-electron-mobility transistors (HEMTs) on 8-in. diameter Si(111) substrate. The fabricated sub-micron gate devices on crack-free AlGaN/GaN HEMT structures exhibited good pin.-off characteristics with a maximum drain current density of 853 mA/mm and a maximum extrinsic transconductance of 180 mS/mm. The device exhibited unit current-gain cut-off frequency of 28 GHz, maximum oscillation frequency of 64 GHz and OFF-state breakdown voltage of 60 V. This work demonstrates the feasibility of achieving good performance AlGaN/GaN HEMTs on 8-in. diameter Si(111) for low-cost high-frequency and high-power switching applications.

Acousto-plasmonic and surface-enhanced Raman scattering properties of coupled gold nanospheres/nanodisk trimers.

This work is devoted to the fundamental understanding of the interaction between acoustic vibrations and surface plasmons in metallic nano-objects. The acoustoplasmonic properties of coupled spherical gold nanoparticles and nanodisk trimers are investigated experimentally by optical transmission measurements and resonant Raman scattering experiments. For excitation close to resonance with the localized surface plasmons of the nanodisk trimers, we are able to detect several intense Raman bands generated by the spherical gold nanoparticles. On the basis of both vibrational dynamics calculations and Raman selection rules, the measured Raman bands are assigned to fundamental and overtones of the quadrupolar and breathing vibration modes of the spherical gold nanoparticles. Simulations of the electric near-field intensity maps performed at the Raman probe wavelengths showed strong localization of the optical energy in the vicinity of the nanodisk trimers, thus corroborating the role of the interaction between the acoustic vibrations of the spherical nanoparticles and the surface plasmons of the nanodisk trimers. Acoustic phonons surface enhanced Raman scattering is here demonstrated for the first time for such coupled plasmonic systems. This work paves the way to surface plasmon engineering for sensing the vibrational properties of nanoparticles.

Plasmonic properties of gold ring-disk nano-resonators: fine shape details matter

Using numerical simulations, we demonstrate that fine shape details of gold nanoring-disks are responsible for significant modifications of their localized surface plasmon properties. The numerical results are supported by optical transmission measurements and by atomic force microscopy. In particular, we found that, depending on the ring wall sharpness, the spectral shift of the ring-like localized surface plasmon resonance can be as large as few hundred nanometers. These results shed the light on the strong sensitivity of the surface plasmon properties to very small deviations of the ring and disk shapes from the ideally flat surfaces and sharp edges. This effect is particularly important for tailoring the surface plasmon properties of metallic nanostructures presenting edges and wedges for applications in bio- and chemical sensing and for enhancement of light scattering.

InGaN∕GaN light emitting diodes on nanoscale silicon on insulator

The authors report on the fabrication of InGaN∕GaN-based light emitting diodes (LEDs) on nanoscale silicon-on-insulator (SOI) substrates. The LED structures are grown on (111)-oriented 45nm thick SOI overlayer by metal organic chemical vapor deposition. Square-shaped mesa patterns are created by standard LED processing steps including multiple-mask photolithography, inductive coupled plasma etching, and contact metallization. Due to the high reflective Si∕SiO2 beneath AlN buffer and high refractive contrasts at the interfaces, the authors observed multiple interference peaks from LEDs on SOI and such effect resulted in an increased integrated electroluminescence intensity when compared to LED structures fabricated on bulk Si(111).

Gold nanoring trimers: a versatile structure for infrared sensing

In this work we report on the observation of surface plasmon properties of periodic arrays of gold nanoring trimers fabricated by electron beam lithography. It is shown that the localized surface plasmon resonances of such gold ring trimers occur in the infrared spectral region and are strongly influenced by the nanoring geometry and their relative positions. Based on numerical simulations of the optical extinction spectra and of the electric near-field intensity maps, the resonances are assigned to surface plasmon states arising from the strong intra-trimer electromagnetic interaction. We show that the nanoring trimer configuration allows for generating infrared surface plasmon resonances associated with strongly localized electromagnetic energy, thus providing plasmonic nanoresonators well-suited for sensing and surface enhanced near-infrared Raman spectroscopy.

Dual wavelength sensing based on interacting gold nanodisk trimers

Fabrication and surface plasmon properties of gold nanostructures consisting of periodic arrays of disk trimers are reported. Using electron beam lithography, disk diameters as small as 96 nm and gaps between disks as narrow as 10 nm have been achieved with an unprecedented degree of control and reproducibility. The disk trimers exhibit intense visible and infrared surface plasmon resonances which are studied as a function of the disk diameter and of the pitch between trimers. Based on simulations of the optical extinction spectra and of the electric near-field intensity maps, the resonances are assigned to a single trimer response and to collective surface plasmon excitations involving electromagnetic interaction between the trimers. The sensing properties of the disk trimers are investigated using various coating media. The reported results demonstrate the possible use of gold disk trimers for dual wavelength chemical sensing.

Micro-Raman probing of residual stress in freestanding GaN-based micromechanical structures fabricated by a dry release technique

In this study, the authors have employed micro-Raman scattering to characterize the residual stress in freestanding GaN-based micromechanical structures on (111)-oriented silicon substrates. Arrays of freestanding cantilevers and microbridges have been fabricated using a combination of dry etching techniques. The Si material beneath the GaN microstructures is removed by a nonplasma XeF2-based dry release technique. Two distinct sets of GaN-based layers on Si(111) with a different amount of growth-induced tensile stress are selected for the fabrication of freestanding cantilevers. The residual stress in these micromechanical structures is determined from the peak shift of the E2-high phonon mode of GaN. Such GaN mechanical structures on Si platforms may be useful for the fabrication of GaN-based microelectromechanical systems and sensors.

Surface micromachined freestanding ZnO microbridge and cantilever structures on Si(111) substrates

In this study, the authors report on the fabrication processes to realize the freestanding ZnO micromechanical structures on Si(111) substrates. Arrays of freestanding cantilevers and microbridges have been fabricated using a combination of dry etching techniques. The mechanical properties of the released ZnO structures are characterized by micro-Raman spectroscopy. The residual stress in these freestanding micromechanical structures is determined from the E2(2) phonon peak shift. Such a method to realize the freestanding structures on Si platform would be useful for the fabrication of ZnO-based microelectromechanical systems and sensors.