C. A. Paulson

Quantitative scanning near-field microwave microscopy for thin film dielectric constant measurement.

We combine a scanning near-field microwave microscope with an atomic force microscope for use in localized thin film dielectric constant measurement, and demonstrate the capabilities of our system through simultaneous surface topography and microwave reflection measurements on a variety of thin films grown on low resistivity silicon substrates. Reflection measurements clearly discriminate the interface between approximately 38 nm silicon nitride and dioxide thin films at 1.788 GHz. Finite element simulation was used to extract the dielectric constants showing the dielectric sensitivity to be Deltaepsilon(r)=0.1 at epsilon(r)=6.2, for the case of silicon nitride. These results illustrate the capability of our instrument for quantitative dielectric constant measurement at microwave frequencies.

Effects of hydrogen implantation damage on the performance of InP/InGaAs/InP p-i-n photodiodes transferred on silicon

Functioning InP/InGaAs/InP p-i-n photodiodes were integrated onto a Si substrate using hydrogen-induced layer transfer process (ion cut) combined with selective chemical etching. This device transfer process minimizes the hydrogen implantation-induced damage and simultaneously improves the transferred surface flatness for device processing. After transfer, the dark current under the reverse bias increased by ∼1.5 times over that of the as-grown photodiodes at −1.5 V, while the photoinduced current was comparable to that of the as-grown sample. These results were discussed in terms of interactions between minority carriers and the remaining implantation-induced damage.

Epitaxial GaN1−yAsy layers with high As content grown by metalorganic vapor phase epitaxy and their band gap energy

GaN1−yAsy epitaxial alloy samples with [N]≫[As] were grown by metalorganic vapor phase epitaxy. The range of As content achieved, up to y=0.067, greatly extends the range of achievable As levels to values that are well within the miscibility gap of the GaN–GaAs system. The single-phase epitaxial nature of the alloy samples was confirmed by x-ray diffraction. The As-content dependence of the band gap was determined by optical absorption measurements. A highly-bowed bandgap was observed as a function of the As content, and a refined value of the bowing parameter of 16.9±1.1 eV was determined.

High crystalline-quality III-V layer transfer onto Si substrate

In this study, an approach combining ion cutting and selective chemical etch for the transfer of high crystalline-quality III-V layers on SiO2∕Si substrate has been investigated. This layer transfer scheme takes advantage of the ion-cutting process by conserving III-V substrates for reuse and simultaneously improving the transferred layer quality and surface condition without using chemical and mechanical polishing. The relocation of the ion-implantation damage maximum enables the transfer of relatively defect-free InP-based layers onto a Si substrate coated with an oxide layer and results in structures ready for further optoelectronic device fabrication or epitaxial growth.

Quadraxial probe for high resolution near-field scanning rf/microwave microscopy

The authors propose and demonstrate a miniaturized quadraxial probe that employs a differential feed technique for use in near-field rf/microwave transmission microscopy. Their quadraxial probe’s electric field measurements show higher electric field localization than a conventional coaxial (monopole) probe. The improved spatial resolution and more sensitive phase measurement of the quadraxial probe versus coaxial probe are further validated by a metal line scan experiment.

Demonstration of near-field scanning photoreflectance spectroscopy

A near-field scanning optical microscope (NSOM) was developed to perform photoreflectance (PR) spectroscopy experiments at high spatial resolution (∼1 μm). Representative PR spectra are shown, along with an image illustrating the capability of observing contrast in images due to the strength of a PR feature. It was found that sufficiently high intensity light from the NSOM tip can produce photovoltages large enough to limit the spatial resolution of the electric field determination by PR. The photovoltage effect is measured as a function of light intensity, and the results are discussed in terms of a simple photovoltage expression.

Near-field scanning optical microscopy investigation of immiscibility effects in In1−xGaxP films grown by liquid phase epitaxy

Near-field scanning optical microscopy (NSOM) and electron probe microanalysis (EPMA) were used to study the topographic and microscopic optical properties of indium–gallium–phosphide (In1−xGaxP) samples grown by liquid phase epitaxy on gallium–arsenide substrates. NSOM imaging found strong and highly localized variations in the photoluminescence (PL) intensity for samples that were highly lattice mismatched with the substrate. The topography and optical features were roughly spatially correlated for these samples. Shifts in the PL peak energy position (by as much as 27 meV) were found during scans across highly mismatched samples, whereas no shifts were seen for In1−xGaxP films with a nearly lattice matched composition. Compositional fluctuations were determined to be the cause of these PL peak energy shifts. EPMA provided corroborating evidence that compositional fluctuations are spatially correlated with the topography. These composition fluctuations arise from the known solid–solid miscibility gap in ...

Atomic Force Microscopy Probe with Integrated Loop and Shielded Leads for Micromagnetic Sensing

The effort to produce an instrument that can achieve high spatial resolution, nondestructive, surface and sub-surface imaging for a variety of materials comes with many challenges. One approach, magnetic resonance-force microscopy (MRFM), lies at the nexus of two sensitive technologies: magnetic force microscopy (MFM) and magnetic resonance imaging (MRI). MFM uses a magnetic tip in a standard atomic force microscope (AFM) to obtain magnetic information about a surface. A difference in the magnetic moments of surface atoms in different regions on the surface varies the cantilever resonance. MRI, on the other hand, uses the spin states of magnetically biased atoms to differentiate between chemical species.

Localized microwave measurement using AFM-compatible scanning nearfield microwave microscope cantilever with ultra-tall coaxial probe

We have demonstrated localized microwave measurements using SNMM cantilevers integrated with ultra-tall coaxial tips. Our results demonstrate improved electromagnetic field confinement with enhanced immunity to the parasitic capacitive coupling that is typically associated with SNMM imaging using cantilever based probes. Dielectric spectroscopy capabilities at microwave frequencies are currently being pursued for material characterization in nanometer scale.

Fabrication and measurements using ultra-tall near-field coaxial tips

We present a new method for microfabrication of coaxial silicon tips with heights >50 /spl mu/m. The coaxial silicon tip acts as an electrically small antenna. Microwave measurements using a microfabricated coaxial tip chip are performed with a network analyzer HP8753D and an atomic force microscope (AFM). Scanning near-field microwave microscopy (SNMM) using the ultra-tall coaxial tip is demonstrated with a commercial AFM silicon probe in noncontact mode as a sample.