Emerging Technologies 2018 Session Listing
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Session E1: Advanced Materials
Start Time: 13:30, Wednesday, May 09
Room: Mt. Currie South
Chaired by Yi-Hwa Liu, Yale University (firstname.lastname@example.org) and Karen Kavanagh, Simon Fraser University (email@example.com)
- 13:30 Rehan Kapadia, University of Southern California
Compound semiconductors on anything
The electronic and photonic circuits and systems that form the backbone of the modern world are predicated on the ability to create high quality semiconductors. Yet, high-performance electronic and photonic grade semiconductors are nearly exclusively grown on lattice matched substrates. This substrate limitation arises due to the fundamental mechanisms of nucleation and growth in state-of-the-art vapor phase growth techniques, which proves to be extremely limiting and costly. Here we demonstrate a platform for growth of compound semiconductors from microscale liquid metal templates. Using these templates, we can control nucleation and growth of these compound semiconductors, enabling single crystalline devices on non-epitaxial substrates. To grow single crystalline material in the desired form-factors, from liquid metal templates on arbitrary substrates presents a significant challenge, as dewetting of the liquid films prevent control over the ultimate material geometry. Through a basic thermodynamic approach, we show that it is possible to control dewetting on nearly any material, and subsequently grow compound semiconductors on these same substrates. Using this approach, we demonstrate growth and characterization of crystalline InP, InAs, and GaP, on silicon nitride, graphene, gadolinium oxide on silicon, and metals.
- 13:50 Giuseppe Greco, National Research Council, Italy
with E. Schilirò, R. Lo Nigro, I. Deretzis, A. La Magna, G. Nicotra, F. Roccaforte, F. Iucolano, S. Ravesi, P. Prystawko,
P. Kruszewski, M. Leszczyński, R. Dagher, E. Frayssinet, A. Michon, Y. Cordier, and F. Giannazzo
2D materials integration with nitrides for high frequency applications
Graphene (Gr) integration with Al(Ga)N/GaN heterostructures has been recently proposed to implement a Hot Electron Transistor (HET), with Gr working as the ultrathin base and the Al(Ga)N/GaN 2DEG as the emitter [1,2]. Although THz operation has been predicted for Gr base HETs, achieving the targeted performances ultimately depends on the structural and electrical properties of the interfaces. Here, two approaches were explored to fabricate Gr/Nitrides heterostructures: the transfer of Gr grown by chemical vapour deposition (CVD) on catalytic metals (Cu) , and the direct CVD growth of Gr on AlN and AlGaN/GaN templates on Si, SiC or sapphire substrates, as well as on bulk AlN [1,2]. Furthermore, different strategies were considered to obtain a base-collector barrier with optimal hot electrons transmission, i.e. the atomic layer deposition of ultra-thin dielectrics (Al2O2, HfO2) or the transfer of thin MoS2 films onto Gr . Finally, arrays of HETs were fabricated by integration of these elementary building blocks. Vertical current transport across the heterostructures was studied by electrical measurements on device test structures and by local CAFM analyses [2,5,6]. In addition, XRD, STEM/EELS, XPS, LEED, Raman and AFM analyses were used to investigate the heterostructures structural/chemical properties. These experimental information were compared with ab-initio DFT calculations of the Gr/Nitride interfacial properties.
 F. Giannazzo, G. Fisichella, G. Greco, A. La Magna, F. Roccaforte, B. Pecz, R. Yakimova, R. Dagher, A. Michon, Y. Cordier, Phys. Status Solidi A, 1700653 (2017).  A. Zubair, A. Nourbakhsh, J.-Y. Hong, M. Qi, Y. Song, D. Jena, J. Kong, M. Dresselhaus, T. Palacios, Nano Lett. 17, 3089 (2017).  G. Fisichella, G. Greco, F. Roccaforte, F. Giannazzo, Nanoscale, 6, 8671 (2014).  G. Fisichella, E. Schilirò, S. Di Franco, P. Fiorenza, R. Lo Nigro, F. Roccaforte, S. Ravesi, F. Giannazzo, ACS Applied Materials & Interfaces 9, 7761-7771 (2017).  G. Greco, F. Iucolano, F. Roccaforte, Appl. Surf. Sci. 383, 324-345 (2016).  G.Greco, P. Fiorenza, F. Iucolano, A. Severino, F. Giannazzo, F. Roccaforte, ACS Appl. Mater. Interfaces 9,35383-35390 (2017).
- 14:10 Guangrui (Maggie) Xia, University of British Columbia
Thermal thinning and Raman spectroscopy in the study of 2D black phosphorus
2D black phosphorus (BP) is a promising material for ultra-thin and flexible electronic and photonic applications. So far, there have not been an effective method in depositing uniform and high quality 2D BP samples, which have been fabricated by thinning from bulk BP. We report a new controllable and scalable approach to prepare high-quality few-layer black phosphorus, which is thermal sublimation. Uniform and crystalline 2 to 4-layer BP with an area from 10 to 1,000μm2 was prepared with this method. No micron scale defects were observed. The uniformity and crystallinity of BP samples after thermal thinning were confirmed by Raman spectra and Raman mapping. The sublimation rate of BP was around 0.18 nm / min at 500 K and 1.5 nm / min at 550 K. Both room and high temperature Raman peak intensity ratio Si/A2g as functions of BP thickness were established for in-situ thickness determination and control. A fast method to determine the BP crystal orientation by angle-resolved Raman spectroscopy with 442 nm excitation will also be presented.
- 14:30 Antoine Fleurence, Japan Advanced Institute of Science and Technology
Epitaxial silicene on ZrB2(0001): a 2D allotrope of silicon
Two-dimensional materials are of great interest for the miniaturization of the electronic devices and the realization of new functionalities. In this perspective, silicene, a graphene-like two-dimensional honeycomb structure made of Si atoms, offers new opportunities to scale down the Si-based nanotechnologies. The analogy of silicene with graphene is reflected by the existence of Dirac cones in the calculated band structure of free-standing silicene. However, in contrast to graphene, silicene was only fabricated in epitaxial forms with electronic and structural properties deviating from those of the free-standing form. Among the few substrates on which silicene has been experimentally observed, (0001)-oriented zirconium diboride (ZrB2) thin films grown on Si(111) have the unique capability of promoting the spontaneous and self-terminating growth of a silicene sheet made of atoms segregating from the Si substrate. In this talk, I will present the structural, electronic and chemical properties of epitaxial silicene, which are stemming from the particular sp2/sp3 hybridization of the orbitals in the two-dimensional allotrope of silicon.
- 14:50 Feng Xiong, University of Pittsburgh
Tuning electrical and thermal transport in two-dimensional materials via electrochemical intercalation
Layered two-dimensional (2D) transition-metal dichalcogenides (TMDs) such as MoS2 have shown great promise for nano- and opto-electronics. The interlayer separation in MoS2 (~0.65 nm) provides perfect sites to accommodate guest species such as alkali metal ions (Li+) through a process known as intercalation. Recently, intercalation has been shown to be an effective technique to reversibly tune material properties of layered 2D films.
In this work, we report an in-situ platform to electrochemically intercalate Li ions into the interlayer spacing of ultrathin MoS2 nanosheets, controllably tuning their electrical and thermal properties. Our in-situ optical and Raman illustrate the dynamics of the electrochemical intercalation process and reveal a reversible 2H to 1T phase transitions in MoS2 upon Li intercalation and de-intercalation. Through Hall measurement, we notice a 100x increase in carrier concentration in Li-intercalated MoS2 due to charge transfer.
We also study cross-plane thermal transport in MoS2 upon intercalation using time-domain thermoreflectance (TDTR). We find that the thermal conductance decreases by a factor of ~7-9x upon lithiation, and is fully reversible upon de-intercalation.
This capability to reversibly engineer the physical and chemical properties of nanomaterials through intercalation is promising and could enable exciting opportunities in optoelectronics, transparent electrodes, energy harvesting and storage.
- 15:10 COFFEE BREAK
(Mt. Curie Foyer)
- 15:30 Byron Gates, Simon Fraser University
Extending the strategies for modifying the surfaces of semiconductor materials and devices
The interfaces of semiconducting materials and their oxides are integral to the design of fabrication routes for preparing freestanding semiconductor materials, such as components in microelectromechanical systems, or the preparation of interfaces for electronic devices that serve as electronic, mechanical or other types of chemical and biochemical sensors. A variety of strategies are used to modify the surfaces of these materials either during or following fabrication processes. The properties that are desired from these interfaces include tuning their ability to repel or retain water, to overcome stiction during fabrication processes or subsequent applications, to resist fouling from biochemical species, to tune the electronic and/or electrochemical properties of their interfaces, and to improve the durability of the underlying materials. A strategy for modifying these materials is introduced in this contribution that are enabling a new approach to tuning the properties and uses of semiconductor materials. These surface modifications are demonstrated for a variety of applications and surface chemistries.
- 15:50 Faisal Mohd-Yasin, Griffith University
Sputtered AlN and ZnO thin films on 3C-SiC/Si substrates for piezoelectric applications
Aluminum Nitride (AlN) and Zinc Oxide (ZnO) thin films have been deposited on a variety of substrates such as silicon, glass, sapphire etc. In this talk, I present the DC and RF sputtering of the said films on epitaxial cubic-silicon carbide-on-silicon substrates. The later were fabricated in-house at Queensland Micro- and Nanotechnology Centre. The effects of the sputtering parameters towards growing highly c-axis structures will be elucidated. The sputtered AlN and ZnO films are suitable for piezoelectric applications. This conclusion is supported by the values of the structural, morphological and mechanical parameters of these materials.
- 16:10 Yvon Cordier, Centre National de la Recherche Scientifique
with Y. Cordier, R. Comyn, E. Frayssinet, M. Lesecq, N. Defrance and J-C. DeJaeger
On the advantages of a lower growth temperature for GaN HEMTs on Silicon
Lower growth temperature is generally considered as a drawback for achieving high crystal quality heteroepitaxial III- Nitrides, but in the case of GaN on Silicon, the necessity to reduce the nucleation temperature of AlN gives molecular beam epitaxy (MBE) the opportunity to demonstrate high performance high frequency devices like Al(Ga)N/GaN high electron mobility transistors (HEMTs). Compared to metal organic vapor phase epitaxy (MOVPE), the control of the interface between the AlN nucleation layer and the substrate is easier and the reduced growth temperature allows to obtain a more electrically resistive interface while keeping good crystal quality. Furthermore, thanks to the high purity of ammonia-MBE, compensation doping is not necessary to achieve resistive buffer layers and we have shown that further reducing the growth temperature of AlN within the nucleation and stress mitigating layers has a noticeable impact on the lateral and vertical buffer leakage currents with resulting vertical breakdown voltage up to 740V in 2 μm thick structures. As a consequence, the buffers of MBE grown HEMT structures exhibit low RF propagation losses (below 0.5 dB/mm up to 70 GHz) while structures regrown by MOVPE on MBE AlN-on-Si templates confirm that the thermal budget is critical for achieving a high resistivity.
- 16:30 Marco Rahm, Technische Universität Kaiserslautern
with J. Kappa, K.M. Schmitt and D. Sokoluk
Grating modulators for terahertz coded aperture imaging
In terahertz science, imaging technologies display the highest technological potential, although they currently lack of data acquisition speed which bars them from a number of key applications on the commercial market. A promising step to overcome these limitations was the introduction of coded aperture imaging techniques into the terahertz frequency domain. Pursuing the ultimate goal to develop imaging terahertz spectroscopes over a wide frequency range, the key challenge is the implementation of spatial light modulators with wide spectral modulation bandwidth and sufficient modulation contrast.
Here, we present a spectrally broadband modulator concept based on a switchable grating in Littrow configuration . We demonstrate that such a modulator can potentially modulate terahertz waves in a frequency range from 1.7 THz to 3 THz at a modulation depth of more than 0.6. Furthermore, we numerically study coded aperture imaging of a binary image and its reconstruction. As a great advantage, the approach allows to dynamically alter the pixel size of the modulator by adjusting the number of micromirrors that define a pixel. By this means, also aperiodic grating structures can be implemented.
1. J. Kappa, K. M. Schmitt, and M. Rahm, Opt. Express 25, 20850 (2017).
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