A5003920888- Semiconductor Quantum Structures and Devices
- Graphene research and applications
- Semiconductor materials and devices
- GaN-based semiconductor devices and materials
- Semiconductor Lasers and Optical Devices
- Advanced Semiconductor Detectors and Materials
- Semiconductor materials and interfaces
- Photonic and Optical Devices
- Quantum and electron transport phenomena
- Nanowire Synthesis and Applications
- Quantum Dots Synthesis And Properties
- Electronic Packaging and Soldering Technologies
- Silicon and Solar Cell Technologies
- Advancements in Semiconductor Devices and Circuit Design
- Chalcogenide Semiconductor Thin Films
- Graphene and Nanomaterials Applications
- Nonlinear Optical Materials Studies
- 2D Materials and Applications
- Ga2O3 and related materials
- Copper Interconnects and Reliability
- Research in Social Sciences
- Integrated Circuits and Semiconductor Failure Analysis
- 3D IC and TSV technologies
- Forensic and Genetic Research
- Laser Material Processing Techniques
University of Helsinki
2001-2024
Institute for Molecular Medicine Finland
2024
Aalto University
2006-2018
Tieto (Finland)
2013-2018
Helsinki Institute of Physics
2008
Abstract Gallium selenide (GaSe) is a layered semiconductor and well-known nonlinear optical crystal. The discovery of graphene has created new vast research field focusing on two-dimensional materials. We report the properties few-layer GaSe using multiphoton microscopy. Both second- third-harmonic generation from flakes were observed. Unexpectedly, even peak at wavelength 390 nm, corresponding to fourth-harmonic or sum frequency pump light, was detected during spectral measurements in thin flakes.
A field-effect device based on dual graphene-GaSe heterojunctions is demonstrated. Monolayer graphene used as electrodes a GaSe channel to form two opposing Schottky diodes controllable by local top gates. The exhibits strong rectification with tunable threshold voltage. Detailed theoretical modeling explain the operation and distinguish differences compared single diode.
Single- and few-layer graphene was studied with simultaneous third-harmonic multiphoton-absorption-excited fluorescence microscopy using a compact 1.55 μm mode-locked fiber laser source. Strong generation (THG) (MAEF) signals were observed high contrast over the signal from substrate. High also achieved between single- bilayer graphene. The measurement is straightforward very fast compared to typical Raman mapping, which conventional method for characterization of Multiphoton proved be an...
We report on the nonlinear optical properties of few-layer GaTe studied by multiphoton microscopy. Second and third harmonic generation from flakes were observed in this study with laser pump wavelength 1560 nm. These processes found to be sensitive number layers. The second- third-order susceptibilities 2.7 × 10−9 esu (1.15 pm/V) 1.4 10−8 (2 10−16 m2/V2) estimated, respectively.
A reproducible route for tuning localized surface plasmon resonance in scattering type near-field optical microscopy probes is presented. The method based on the production of a focused-ion-beam milled single groove near apex electrochemically etched gold tips. Electron energy-loss spectroscopy and scanning transmission electron are employed to obtain highly spatially spectroscopically resolved maps probes, revealing at visible near-infrared wavelengths. By changing distance L between probe...
We have established Raman fingerprint of GaTe and GaSe to investigate their crystal quality. As unencapsulated, they both oxidise in ambient conditions which can be detected analysis. X-ray photoelectron spectroscopy (XPS) analysis shows a good agreement with 50-nm-thick Al2O3 encapsulation layer deposited by atomic deposition (ALD) inhibits degradation conditions.
Graphene electro-optic modulators (GEOMs) are emerging as a viable alternative to conventional material-based mainly due their broadband and ultrafast performance. These GEOMs with combined advantages of small footprint low energy consumption can potentially enable various high-performance applications that not possible using approaches. Here, we report the first actively Q-switched lasers GEOM. In contrast previously reported passively modulated by two-dimensional layered saturable...
Flexible electronics serve as the ubiquitous platform for next-generation life science, environmental monitoring, display, and energy conversion applications. Outstanding multi-functional mechanical, thermal, electrical, chemical properties of graphene combined with transparency flexibility solidifies it ideal these Although vapor deposition (CVD) enables cost-effective fabrication high-quality large-area films, one critical bottleneck is an efficient reproducible transfer to flexible...
A methodology for the structural analysis of graphene‐related materials using parameterized principal component (PCA), ideal large‐scale data treatment, is introduced. First, we review different aspects Raman spectroscopy and functional characterization sp 2 ‐bonded carbon materials, which are important understanding problem. The PCA then introduced applied to scenarios: identify structures graphene samples with numbers layers. Automating these techniques desired industrial applications....
Metal–graphene contact resistance is a technological bottleneck in the realization of viable graphene-based electronics. We report model that useful for finding gate-tunable components this resistance, determined by tunneling carriers between 3D metal and 2D graphene underneath, followed Klein to channel. This quantifies intrinsic factors control including effect unintended chemical doping. Our results agree with experimental several metals.
Transformation of self-assembled InAs quantum dots (QDs) on InP(100) into rings (QRs) is studied. In contrast to the typical approach III--V semiconductor QR growth, QDs are not capped form rings. Atomic force micrographs reveal a drastic change from after growth interruption in tertiarybutylphosphine ambient. Strain energy relief QD discussed and mechanism for dot-to-ring transformation by As/P exchange reactions proposed.
In this work, low temperature growth of GaAs epitaxial layers on Ge substrates by metalorganic vapor phase epitaxy has been studied. The experiments show that a 530°C and V/III ratio 3.5 result in smooth surfaces. Atomic force micrographs do not any anti-phase boundaries the surface grown misoriented substrate. X-ray diffraction curves layer tilt is reduced as lowered. Synchrotron topography reveals very threading dislocation densities 300 cm -2 for layers. Additionally, no misfit...
In this paper, low energy electron beam (5–20 keV, 0–500 μAs/cm2) induced damage on a GaN/InGaN/GaN near-surface quantum well structure is studied. Exposure to shown significantly reduce the optical quality of structure. It also observed that reducing causes larger PL intensity reduction. This can be explained by considering penetration depth, which smaller with lower e-beam energies. The believed attributed enhanced dislocation mobility upon irradiation. However, further studies are needed...
This paper examines the utilization of plasma-enhanced atomic layer deposition grown AlN in fabrication a high-k insulator on GaAs. It is shown that GaAs MIS capacitors with an unpinned Fermi level can be fabricated utilizing thin ex-situ deposited passivation layer. The illumination and temperature induced changes inversion side capacitance, maximum band bending 1.2 eV indicates capacitor reaches inversion. Removal surface oxide not required contrast to many common approaches.
We demonstrate nonlinear behavior in three-terminal T-branch graphene devices at room temperature. A rectified output the center branch is observed when device biased by a push–pull configuration. Nonlinearity assumed to arise from difference charge transfer through metal–graphene contact barrier between two contacts. The sign of rectification can be altered changing carrier type using back-gate voltage.
We present prominent tunable and switchable room-temperature rectification performed at 100 kHz ac input utilizing micrometer-scale three-terminal junction field-effect devices. Monolayer CVD graphene is used as both a channel gate electrode to achieve all-graphene thin-film structure. Instead of ballistic theory, we explain the characteristics through an electric-field capacitive model based on self-gating in high source–drain bias regime. Previously, nanoscale junctions with (or...
Abstract The paternally inherited Y chromosome is highly informative of genetic ancestry, therefore making it useful in studies population history. In Finland, two Y-chromosomal haplogroups reveal the major substructure population: N1a1 enriched northeast and I1a southwest, suggested to reflect eastern western ancestry contributions population. Yet, beyond these lineages, distribution finer-scale variation has not been assessed Finland. Here, we provide most comprehensive study among Finns...
Using single-layer CVD graphene, a complementary field effect transistor (FET) device is fabricated on the top of separated back-gates. The local back-gate control transistors, which operate with low bias at room temperature, enables highly tunable characteristics due to separate over electrostatic doping channels. Local back-gating allows level independently supply voltage, operation very VDD. Controllable also allow compensation variation in unintentional typically observed graphene....
Abstract This paper presents X‐ray diffraction and atomic force microscopy investigation of GaP thin films grown on silicon (100) substrate by metalorganic vapour phase epitaxy. Crystalline has been two‐step growth method, in which first a low temperature nucleation layer is at 475 °C, then, 100‐nm‐thick 700 °C. The comprised trenches smooth terraces are attributed to anti‐phase domains. Without the forms cross‐hatch pattern wires. Formation wires anisotropic diffusion, thus, grow along...
We report the synchronization of two actively Q-switched fiber lasers operating at 1.5 μm and 2 with a shared broadband graphene electro-optic modulator. Two monolayer sheets separated high-kHfO2 dielectric layer are configured to enable light modulation. The modulator is by optical laser cavities (i.e., an erbium-doped cavity thulium/holmium-codoped cavity) Q-switch lasers, resulting in stable synchronized pulses repetition rate ranging from 46 kHz 56 kHz.
White beam synchrotron x-ray topography (WBSXRT) is a non-destructive technique, which capable of analysing the strain and/or dislocation distribution in single crystal materials. This paper discusses application WBSXRT to analysis fields due microelectronic packaging integrated circuits. A ball grid array package containing an Intel® Pentium® III microprocessor was employed investigate spatial extent imposed on underlying silicon substrate reflow process for lead–tin solder bumps.