AVS 66 Session TF+EM+MI-TuM: Thin Films for Microelectronics, Photonics, and Optoelectronic Applications

Tuesday, October 22, 2019 8:00 AM in Room A122-123

Tuesday Morning

Session Abstract Book
(345KB, Apr 26, 2020)
Time Period TuM Sessions | Abstract Timeline | Topic TF Sessions | Time Periods | Topics | AVS 66 Schedule

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8:00 AM TF+EM+MI-TuM-1 Monolithic Integration of III-Vs on Si for Electronic and Photonic Applications
Philipp Staudinger, Svenja Mauthe, Noelia Vico Trivino, Marilyne Sousa, Clarissa Convertino, Yannick Baumgartner, Preksha Tiwari, Heinz Schmid, Kirsten Moselund (IBM Research Zurich, Switzerland)

For more than half a century researcher have been working on monolithic integration of III-V materials on Si in order to achieve seamless integration of III-V with Si CMOS. Progress has been made in recent years for example on nanowires [1], aspect ratio trapping (ART) [2] and other selective growth techniques suitable for III-V device integration. Here, I will discuss our work on Template-Assisted Selective Epitaxy (TASE) [3], as a novel epitaxial technique where III-V nanostructures are grown within an oxide template.

In this method we first use a combination of lithography and etching to define our structures in Si. These might be vertical or lateral nanowires, or more exotic shapes such as hall-bars, rings and disks. The Si features are covered by an oxide, which is opened locally, and the Si is partially etched exposing a Si nucleation seed within a hollow oxide cavity (template). The template is subsequently filled by metal-organic chemical vapor deposition (MOCVD) grown III-V material. The geometries of the III-V features are lithographically defined by the shape of the hollow template and to a large extent independent of growth conditions.

The versatility of this technique will be shown through several experimentally demonstrated devices, such as InGaAs MOSFETs [4], heterojunction tunnel FETs [5] and monolithically integrated room temperature optically pumped GaAs [6] and InP microdisk lasers [7].

The quality of the TASE-grown material is assessed by high-resolution scanning transmission electron microscopy (HR-STEM). Devices are free from propagating defects and dislocations, but stacking faults are present as expected for selective epitaxy. By controlling the twinning, we were successful in demonstrating pure wurtzite InP micro-substrates for the first time. We also compare lasing performance to that of devices based on defect-free bonded material, which currently represents the state-of-the-art in terms of photonic integration.

This work received funding from H2020 ERC project PLASMIC (Grant No. 678567), SiLAS (Grant No. 735008) and the SNF (Project 200021_156746).

1. B. Mayer et al., Nano Lett., vol. 16, no. 1, pp. 152–156, 2016.

2. Z. Wang et al., Nat. Photonics, vol. 9, pp. 837–842, 2015.

3. H. Schmid et al. Appl. Phys. Lett. 2015, 106 (23), 233101.

4. L. Czornomaz et al., Symp. VLSI Tech., 2015, pp. T172–T173, 2015.

5. Cutaia, D. et al., Symp. VLSI Tech., pp. 403-407, (2016).

6. S. Wirths et al., ACS Nano 12 (3), pp. 2169, 2018.

7. S. Mauthe et al., submitted to IEEE J. Sel. Top. Quantum Electron. (2019).

8. M. Sousa et al. , 2018 IEEE Nano, DOI: 10.1109/NANO.2018.8626223

9. P. Staudinger et al., Nano Letters, vol. 18 (12), 7856, 2018.

8:40 AM TF+EM+MI-TuM-3 A Scheme for Better Future Technology by developing AlGaN based Highly Responsive Photosensing Devices
Neha Aggarwal, Shibin Krishna, Lalit Goswami, Govind Gupta (CSIR-National Physical Laboratory, India)
All species on Earth are affected by UV radiation, from environment-to-humans, industrial-to-residential, defense-to-technology; a number of current & futuristic applications of detecting UV radiation exist. For fabricating UV photodetectors (PDs), III-Nitrides are promising candidates due to their superior material properties such as wide-direct bandgap, high thermal conductivity, good radiation hardness, etc. Also, III-nitrides are intrinsically blind to the visible region of EM spectrum; thus, do not require expensive optical filters unlike existing Si-based UV PDs. Among nitrides, AlGaN based heterostructures have gained huge interest in optoelectronic applications due to their ability to tune the bandgap by modulating Al concentration which allows them to select the cut-off wavelength depending upon the application. Further, to facilitate the integration of AlGaN based devices with existing Si technology, Si substrates were utilized for growing AlGaN heterostructures. However, large lattice mismatch between AlGaN & Si may restrict the growth of defect-free AlGaN, thus a nucleation layer is needed to avoid cracking due to tensile strain. Incorporation of AlN as interlayer reforms the tensile stress in AlGaN layer directly grown on Si into compressive stress which yields the desired crack-free epitaxial structure. In this work, extensive efforts are employed to grow AlN on Si (111) substrate via PAMBE & successfully accomplished best quality AlN with lowest HRXRD FWHM of 15 arcmin having screw dislocation density of 8.5×108 cm−2. Then, we have performed hetero-epitaxial growth of AlxGa1−xN on AlN buffered Si (111) for x in 0.30-0.45 range & discusses the compositional fluctuations associated with changes in buffer growth parameters. As the buffer growth conditions changes, Al composition varies from 0.30-0.45 & FWHM is reduced from 55.6 to 36.4 arcmin. To realize a highly responsive UV PD, uniformly oriented AlGaN nano-islands are grown aimed to efficiently absorb photons due to increased surface-to-volume ratio. On this, we also implemented interdigitated (ID) electrode configuration to collect higher photo-generated charge carriers. The fabricated AlGaN UV PDs having cut-off wavelength of 284 nm yielded a significant enhancement in responsivity from 36.4 to 140.5 A/W at 2 V bias upon changing electrodes from non-ID to ID. However, the developed UV detection device exhibit high response towards UV with responsivity value of 182 mA/W under 2.5 V bias which is better than the commercially available UV detectors. Conclusively, the highly responsive AlGaN UV-PD on Si displays potential application in the development of advanced optoelectronic devices.
9:00 AM TF+EM+MI-TuM-4 Correlating the Optical Property Evolution in the Au-Ni Binary Thin Films: From Metastable Solid Solution to Phase Separated Alloy
Robyn Collette, Yueying Wu, Philip D. Rack (University of Tennessee Knoxville)

Surface plasmon resonances can be sustained by metallic nanostructures and have been explored for potential optoelectronic device applications. Metallic alloys provide a pathway to tune the plasmonic response of a material. Additionally, alloying may allow for multifunctional materials to be realized. For example, Au-Ni alloys may combine the magnetic properties of ferromagnetic Ni with the plasmonic properties of Au. However, limited studies have been conducted on Au-Ni alloys for use in plasmonic devices. Since the behavior of the alloys depends on the structure, it is first critical to understand the relationship between the structure and the optical properties of the alloy.

In this study, the optical properties of Au1-xNix alloy thin films are investigated by employing a combinatorial sputtering approach. The dielectric function is measured using spectroscopic ellipsometry and is correlated to the composition (energy dispersive x-ray spectroscopy), and phases present (x-ray diffraction). As-deposited alloys form a metastable solid solution, however, annealed alloys exhibited phase separation into Au-rich and Ni-rich phases due to the large miscibility gap in the Au-Ni material system. The optical properties are then rationalized by modeling the dielectric function of the solid solution alloys with a Drude-Critical Point analytical model. Lastly, the efficacy of the model is demonstrated which shows that the dielectric function of the phase separated alloys may be approximated using a composition-weighted average of two solid solution dielectric functions.

9:20 AM TF+EM+MI-TuM-5 Integration of Electro-optically Active BaTiO3 and BaxSr1-xTiO3 with Buffered Si (001) by Chemical Methods
John G. Ekerdt, Bryce Edmondson, Edward Lin (University of Texas at Austin); Sunah Kwon (University of Texas at Dallas); Alexander Demkov (University of Texas at Austin); Moon J. Kim (University of Texas at Dallas)

Recent investigations into thin film BaTiO3 (BTO) show it is a promising candidate for on-chip photonic devices due to its large linear electro-optic (EO) coefficient (r > 100-1000 pm/V) relative to more conventional photonic materials such as LiNbO3 (~30 pm/V) or strained Si (~2 pm/V). However, such high coefficients are achieved only by costly and inherently un-scalable physical vapor deposition techniques. In recent studies, we have investigated chemical routes to the integration of electro-optically active BTO thin films with Si, which offer faster and more scalable methods of deposition. Specifically, atomic layer deposition (ALD) of 40 nm BTO films and chemical solution deposition (CSD) of 85 nm BTO films on SrTiO3 (STO) templates on Si (001) prepared by molecular beam epitaxy (MBE) yield epitaxial BTO films with microstructure and defect nature markedly different from physical deposition techniques. Furthermore, we explored CSD of c-axis in-plane BaxSr1-xTiO3, which is difficult to achieve by physical methods and offers unique insight into the EO behavior of this highly tunable dielectric. X-ray diffraction and scanning transmission electron microscopy confirmed epitaxial, distorted tetragonal structures with a range of structural defects, and electrical and electro-optical measurements showed diminished ferroelectricity and EO response compared to MBE-grown thin films or bulk BTO. ALD-grown films exhibited optical hysteresis with coercivity of ~10 kV/cm, an effective linear EO coefficient of 26 pm/V for 40 nm films, and leakage currents caused by oxygen vacancies. CSD-grown films did not show evidence of ferroelectric hysteresis but maintained EO response with a coefficient of 25 pm/V and had very low leakage current. Past reports of chemical vapor deposited films yielded an EO coefficient of 7 pm/V. These results provide further understanding into the relationship between film structure and linear EO behavior.

9:40 AM TF+EM+MI-TuM-6 Nonlinear Optical Properties of TiO2-based ALD Thin Films
Theodosia Gougousi, Robinson Kuis, Isaac Basaldua, Paul Burkins, Jaron Kropp, Anthony Johnson (University of Maryland, Baltimore County)

Nonlinear materials in thin film form are highly desirable for the development of ultrafast all-optical system on-a-chip platforms, optical frequency converters and optical limiting applications. Conventional nonlinear optical (NLO) materials are usually cut from bulk crystals or are liquids that are not suitable for integration with the contemporary semiconductor industry process flow. The third order nonlinear response of ALD TiO2-based films is investigated using thermally managed Z-scan technique. Some of the as-deposited films exhibit very high nonlinear response which is orders of magnitude higher than conventional nonlinear optical materials such as silica fibers and CS2. Thermal treatment of the films at 450°C for 3 hours in an oxygen rich atmosphere affects the films’ optical properties and results in the loss of the high nonlinear optical response. TiO2 films deposited by Physical Vapor Deposition (PVD) from a 99.9% TiO2 target at room temperature are used as control samples and their nonlinear optical response is found below the detection limit of the Z-scan setup. This extraordinary nonlinear optical behavior of the TiO2 ALD films is linked to the presence of a very small at. % of TiN bonding in the film. We will present detailed characterization of these films by x-ray photoelectron spectroscopy, x-ray diffraction and UV-Vis absorption. The high level of control of the nonlinear index of refraction, n2, using the deposition process coupled with the ability of ALD to coat nonplanar geometries with atomic level precision and the fact that these processes are CMOS compatible have the potential to provide a breakthrough in optical device design and applications.

View Supplemental Document (pdf)
10:00 AM BREAK - Complimentary Coffee in Exhibit Hall
11:00 AM TF+EM+MI-TuM-10 Atomic Layer Deposition on Hexagonal Ge and SiGe Nanowires for Surface Passivation
Willem-Jan Berghuis (Department of Applied Physics, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands); Erwin Kessels, Jos Haverkort, Erik Bakkers, Alain Dijkstra, Elham Fadaly, Marcel Verheijen (Eindhoven University of Technology, The Netherlands)

Semiconductor nanowires (NWs) are nanoscale rods with a typical length of a few microns. They are made of materials such as Ge, Si, InP, GaAs. Due to their high aspect ratio, nanowires have a very high surface-to-volume-ratio, which leads to a large influence of the surface on their electronic and optical properties. Surface states facilitate recombination of electron-hole pairs, which reduces the photovoltaic conversion efficiency of NW solar cells [1] or which decreases the output of NW based LEDs or lasers. The surface can also induce space charge regions in the nanowires, which greatly affects their conductivity and which can be critical in for example sensing applications [2]. To reach the desired performance of nanowires in their applications, it is important to control the surface effects.

Atomic layer deposition (ALD) is a deposition technique that allows for preparation of ultrathin films with sub-nanometer thickness control and with an excellent conformality on high aspect ratio structures such as nanowire arrays. For these reasons ALD is a suitable technique to cover nanowires with thin films to control the surface properties.

Recently, nanowires have enabled the growth of Ge and SiGe in the hexagonal diamond crystal phase [3]. In contrast to the cubic crystal phase of these materials, the hexagonal crystal phase leads to a direct bandgap. The latter makes this material an interesting candidate to realize solid-state lasers that are compatible with the current silicon-based electronics. One of the important steps to accomplish this is to reduce the surface recombination losses; i.e. to passivate the surface.

The aim of this work is to explore the surface passivation of these hexagonal Ge and SiGe nanowires. We do so by covering the nanowires with ultrathin films of Al2O3 prepared by thermal and plasma-assisted ALD (PE-ALD). Secondly, we cover the wires with a stack of POx/Al2O3. The latter is a relatively new passivation scheme that has proven very successful for the surface passivation of InP nanowires [4] and Si wafers [5]. The change in photoluminescence (PL) of the nanowires as a function of the ALD films has been studied to assess the surface passivation and the influence of various pre- and post-treatments. Conformal coating of hexagonal Ge nanowires has been realized and we have observed an improvement of the photoluminescence for NWs covered with PE-ALD Al2O3 and POx/Al2O3.

View Supplemental Document (pdf)
11:20 AM TF+EM+MI-TuM-11 Oxidation Studies of Silicon Germanium (SiGe) using In-Situ Steam Generated (ISSG) and Plasma Enhanced Atomic Layer Deposited (PEALD) Oxides
Yi Song, Shahab Siddiqui, Curtis Durfee, Abraham Pana, Juntao Li, Michael Belyansky, Sebastian Naczas, Erin Stuckert, Liying Jiang, James Demarest, Veeraraghavan Basker, Dechao Guo, Huiming Bu (IBM Research Division, Albany, NY)
SiGe is a versatile material for the semiconductor industry for sub-7 nm node technology development; it can be used as a high mobility channel material in FinFET, and as multiple sacrificial layers to form channel regions in gate all around (GAA) nanosheet device architecture. Understanding SiGe film oxidation is important for matching oxidation rates between SiGe layers with different Ge% in nanosheet applications [1]. In this paper, a study of ISSG (800 oC) and PEALD (room temperature to 300 oC) oxidation processes is performed on blanket Si1-xGex films ranging from x = 0.25 to 0.80. We establish the boundaries of three distinct regions of oxidation behavior for the ISSG process (Region I: 0 < x < 0.5, Region II: 0.5 < x < 0.67, and Region III: x > 0.67). Historically, low Ge oxidation has been extensively studied [2-4]. Here, we show for Region I, the ISSG oxidation rate is very small (1.7 nm of oxide growth in 5 sec). The oxidation rate rapidly increases in Region II as x increases, where it reaches a maximum (13.8 nm in 5 sec) at the Region II/Region III boundary, then abruptly drops in Region III as x increases due to complete sublimation of Ge (see Figure 1). The abrupt increase in the ISSG oxidation rate between Regions I and II makes it difficult to match oxide thicknesses for the wide range of Ge% utilized by nanosheet device architecture. Therefore, we studied a lower temperature oxidation process (PEALD) which has a lower oxidation rate. We found that PEALD oxidation rates are unchanged across the Region I/II boundary, even for higher temperatures up to 300 oC as shown in Figure 2. This enables oxide thickness matching for a wide range of Ge%. These results are applicable to the development of various nanotechnologies such as nanosheet and high mobility channel FinFET devices. View Supplemental Document (pdf)
11:40 AM TF+EM+MI-TuM-12 Precision Defect Engineering of Metal/Insulator/Metal (MIM) Diodes using Localized ALD Transition Metal Impurities in Al2O3 Tunnel Barriers
Konner Holden, Yitong Qi, John F. Conley, Jr. (Oregon State University)

Thin film MIM tunnel diodes are receiving increased interest for high-speed applications such as THz detection and rectenna based energy harvesting. Traditionally, current density vs. field (J-ℰ) asymmetry (ƒasym = J-/J+) with MIM diodes has been achieved through metal work function differences (ΔΦM). Recently, nanolaminate insulator tunnel barrier MIIM diodes enabled by ALD showed improved ƒasym, non-linearity, and responsivity at low voltage by step tunneling through the wider bandgap (EG) insulator to the conduction band of the narrow EG insulator.1 Intrinsic defects present in narrow EG insulators were later demonstrated to further improve low ℰ asymmetry via defect enhanced direct tunneling, when paired with an insulator dominated by tunneling.2,3 In this work, we investigate the impact of localized extrinsic defects by using ALD to intentionally introduce Ni at precise intervals in an Al2O3 tunnel barrier.

ALD of Al2O3 on TiN was performed at 200 °C using TMA and H2O. Five samples were prepared in which a 100 cycle Al2O3 ALD sequence was interrupted by two cycles (c) of Ni(tBu2DAD)2 and O3 after 25, 50, 75, and every 25 c of Al2O3. As-deposited MIM devices were tested with bias applied to an Al top electrode (Fig. 1).

DC J-ℰ sweeps of the 100 c device show Fowler-Nordheim tunneling (FNT) at high ℰ, with ƒasym > 1 due to ΔΦM ≈ 0.2 eV (Fig. 1). The addition of Ni cycles in all cases leads to an increase in J at low ℰ vs. the 100 c Al2O3 device, suggesting defect related conduction. At high ℰ, however, J of all Ni devices is lower than the 100 c device, suggesting suppression of FNT. The 25/2/75 and 75/2/25 (Al2O3/Ni/Al2O3) devices show ƒasym opposite of the 100 c device, while the 50/2/50 and 25/(2/25)x3 devices are roughly symmetric (Fig. 1). The greater reduction in J at large negative ℰ, ƒasym reversal, and reduced J-ℰ slope for the 25/2/75 and 75/2/25 devices suggest that FNT is suppressed more for emission from the smaller ΦM electrode (Al) than for TiN. FNT suppression appears greatest for the 75/2/25 device in which Ni is closest to the Al, pointing to an increase in effective barrier height, likely due to negative charge in the Al2O3. Capacitance (C) vs. ℰ sweeps (Fig. 2) reveal a positive voltage shift in Cmin for all Ni devices, consistent with negative charge.

The asymmetry reversal demonstrates the possibility of precision defect engineering of MIM tunnel devices using ALD. An in-depth discussion of J-ℰ and C-ℰ, temperature-IV, frequency-CV, other impurities, and annealing will be presented.

1. Alimardani et al., APL 102 143501 (2013).

2. Alimardani et al., JAP 116, 024508 (2014).

3. Alimardani and Conley, Jr., APL 105, 082902 (2014). View Supplemental Document (pdf)
12:00 PM TF+EM+MI-TuM-13 Improvement in the Electrical Characteristics of a-ZTO based TFTs via Microwave Assisted Annealing of Channel Layer
Sunil Uprety, Min Khanal, Horyun Lee, Shatila Sarwar (Auburn University); Ashwanth Subramanian (Stony Brook University); Ehsaan Hassani, Tae-Sik Oh, Xinyu Zhang (Auburn University); Chang-Yong Nam (Brookhaven National Laboratory); Minseo Park (Auburn University)

In this research, we have investigated the effect of microwave-assisted annealing of amorphous zinc tin oxide (a-ZTO) channel layers on the electrical characteristics of the thin film transistors (TFTs). A multi-stacked a-ZTO layer was deposited on the oxidized Si wafer using sol-gel process. The precursor solution was prepared by dissolving zinc acetate dihydrate and tin chloride dihydrate into methoxyethanol. The solution was spin coated and calcined in a hot plate at 285°C. The as-calcined a-ZTO wafers were microwave annealed. The microwave (MW) annealing was carried on a commercial microwave oven at different power levels with the sample placed in a kiln which acts as a susceptor. The films remained amorphous even after MW annealing, which was evidenced by X-ray diffraction. The devices were fabricated using the microwave-annealed and as-calcined samples. Hall measurement is being carried out to study the concentration and mobility of charge carries. The performance of the TFTs with as-calcined and MW annealed channel layers were compared. Improvement in the electrical characteristics of the TFTs with MW annealed films were noted. It is believed that the microwave irradiation may promote the enhancement of the electrical characteristics of TFTs. Further research is being pursued to elucidate the role of microwave annealing in improvement of the device performance.

Session Abstract Book
(345KB, Apr 26, 2020)
Time Period TuM Sessions | Abstract Timeline | Topic TF Sessions | Time Periods | Topics | AVS 66 Schedule