Session Chair: Detlev Grützmacher, Peter Grünberg Institut, Forschungszentrum Jülich
1:30pm - 2:00pm Invited
GeSn Mid-Infrared Photonics
National Chung-Cheng University, Taiwan
Group-IV based electronic-photonic integrated circuit (EPIC) operating in the mid-infrared (MIR) region (1.55-8μm) is a new technology for communication applications. Si-based GeSn heterostructures are promising candidates to create new MIR photonic devices for this purpose. Incorporating Sn into Ge can effectively modulate the bandgap energy, thus offering unique advantages for developing basic building blocks including light emitters and photodetectors for MIR EPICs. Here we present our recent results and discuss the use of GeSn heterostructures developing new MIR photonic devices. Low-temperature molecular beam epitaxy (MBE) technology is employed to grow high-quality, high Sn-content GeSn/Ge heterostructures on Si substrates. Light emitters and photodetectors based on GeSn/Ge heterostructures are also fabricated and characterized. The results show that, increasing the Sn content can effectively redshift the emission wavelength into the MIR region. In addition, GeSn-based photodetectors with a Sn content of >5% exhibit an extended cutoff wavelength beyond 2000 nm. These results demonstrate the feasibility of GeSn-based photonic devices for MIR EPIC applications.
2:00pm - 2:30pm Invited
Inverse Design of Si Nano Materials for Optoelectronic and Spintronic Applications
Institute of Semiconductors, Chinese Academy of Sciences, China
The Materials Genome Initiative (MGI) was lunched to help businesses discover, develop, and deploy new materials twice as fast. Semiconductors playing a key role in a wide assortment of technologies and industries ranging from economy, human well being, and national security are essential part of the materials genome initiative. Here we present demos of semiconductor materials genome to accelerate the development of Si-based light emission and spintronics. (1) Receipts for optics-friendly silicon. Si is the darling of the microelectronics industry, but it has an Achilles’ heel: Si can not absorb or emit light without the help of phonons. This so-called indirect band gap makes it an inefficient option for light-emitting diodes and solar cells. On the other hand, there is an urgent requirement for an optical emitter that is compatible with standard, silicon-based ultra-large-scale integration technology. The discovered Si/Ge magic sequence superlattices or core/multishell nanowries exhibit orders more efficient at absorbing (emission) light than their existing counterpart records and approach more than 10% brightness of real direct gap materials, such as GaAs. In principle, such magic sequence superlattice could be prepared with molecular beam epitaxy, and the nanowire can be prepared by selective area metalorganic vapor phase epitaxy. Enhanced valley splitting towards a spin qubit in Si. (2) Electronic spins in Si are raising contenders for qubits -- the logical unit of quantum computation-- owing to its outstanding spin coherence properties and compatibility to standard electronics. A remarkable limitation for spin quantum computing in Si hosts is the orbital degeneracy of this material's conduction band, preventing the spin-1/2 states from being an isolated two-level system. Very recently, we numerically inverse designed Si quantum well to isolating a single electron valley state in Si by a magic-sequence of Ge/Si barrier layers.
2:30pm - 2:45pm Oral
Investigating Ferroelectric Behavior of Nanoscale Perovskites using Scanning Probe Microscopy Techniques
Rajasekaran GANESHKUMAR1, Suhas SOMNATH2, Chin Wei CHEAH1, Stephen JESSE2, Sergei V KALININ2, Rong ZHAO1
1Engineering Product Development, Singapore University of Technology and Design, Singapore; 2Center for Nanophase Materials, Oak Ridge National Laboratory, United States
Perovskite ferroelectrics remains one of the technologically important group of materials. In the last several years, a material system was claimed ferroelectric in nature by interpreting the electromechanical response obtained using a Piezoresponse force microscopy (PFM). However, there is a great deal of ambiguity in the existing reports on nanoscale system as the PFM hysteresis loops can originate from a number of alternate mechanisms. Here, we systematically investigate the ferroelectric behaviour of electrospun potassium niobate (KNO) nanofibers using various scanning probe microscopy techniques. Band excited (BE) scans revealed that PFM signals are dominated by changes in resonant frequency due to rough surfaces, rather than the actual piezo-response amplitude. Contact-mode Kelvin Probe Force Microscopy experiment was performed to identify the alternate signal origins such as tip-induced charge injection and electrostatic forces between the tip and nanofiber surface. Furthermore, impact of relative humidity (RH) on the KNO nanofiber’s local piezoelectric strength, switching behaviour and tip-induced charges was explored. These observations will provide a clarity in studying newly developed nanoscale ferroelectrics, especially crucial to materials with low piezoelectric coefficients.
2:45pm - 3:00pm Oral
Directly Synthesis of Mn-Doped Silicon Nanowires via the Vapor-Liquid-Solid Mechanism
1National Taiwan University, Taiwan; 2Center for Condensed Matter Sciences, Taiwan; 3National Synchrotron Radiation Research Center, Taiwan
It’s expected that diluted magnetic semiconductors (DMSs) exhibit both the electronic transport properties and spintronic characteristics. It has been reported that room temperature ferromagnetism is present in Mn+-implanted Si nanowires, showing that low dimensional DMSs are potentially useful for future spintronic device applications. However, ion implantation may produce unwanted defects that could degrade the device performance. In this work, we therefore attempt to directly synthesize high quality Mn-doped silicon nanowires via the Vapor-Liquid-Solid growth method. We use Cs-corrected scanning transmission electron microscopy to analyze the morphology and compositional distribution of as-grown nanowires. Magnetic properties of the nanowires are measured by electron spin resonance instrument, and the concentration of Mn is measured by synchrotron radiation based X-ray absorption spectroscopy. We use Au-Mn (Au:Mn = 9:1) binary liquid alloy catalyst to grow Si nanowires at 600°C. However, due to the low solubility of Mn and slow diffusion kinetics of Mn in Si crystal, effective doping of Mn in crystalline Si nanowires cannot be achieved at the typical nanowire growth temperatures. High-temperature anneal (>900°C) of the nanowires in vacuum may cause severe morphology change of nanowires. We therefore anneal the nanowires in air to form a stable oxide shell surrounding the nanowires at 900°C to avoid the morphology change of nanowires. The subsequent fast diffusion of Mn forms Mn silicide near the catalyst in the nanowires. The nanowires may present magnetic properties for spintronic application.
3:00pm - 3:15pm Oral
Comparison of Low Temperature Silane-based Silicon Oxides from 100°C to 300°C
Hou Jang LEE, Bi-Rong, Michelle CHEW
Institute of Microelectronics, Agency for Science Technology and Research (A*STAR), Singapore
Silane-based silicon oxides with deposition temperatures ranging from 100°C to 300°C have been analyzed and characterized using FTIR, AFM and EDX analysis. Their dry etch and wet etch rates have also been characterized for comparison. These silane oxides were all deposited in the same PECVD (Plasma Enhanced Chemical Vapor Deposition) reactor chamber with capacitively coupled plasma. During deposition the wafer sat on a resistively heated bottom electrode. The deposition temperature of the film was determined by the temperature of the heated bottom electrode, which varied from 100°C to 300°C. As the deposition temperature increased from 100°C to 300°C, the deposition rate decreased correspondingly but not linearly. Higher deposition temperature resulted in lower deposition rates for the silicon oxide. At the same time, the dry etch rates of silicon went down with higher deposition temperatures, indicating that the silicon oxide became denser and more robust with higher deposition temperatures. Nevertheless, it was possible to deposit silicon oxide at temperatures as low as 100°C. Such low temperature silicon oxide films are suitable for potential applications on MEMS (Microelectrical Mechanical Structures), TSV’s (Through Silicon Vias) as well as the bonded wafers that require low processing temperature silicon oxide films.