Fluorine-doped indium oxide (IO) nanocubes separated by nanometric gaps constitute a versatile system hosting high-quality mid-infrared plasmons with potential application in optoelectronics and light harvesting. In this theory-experiment combined work, we predict large tunability of these hybridized plasmon modes by controlling the gap size and the dimensionality of the gap region. We confirm this prediction through electron energy-loss spectroscopy (EELS) measurements performed in a scanning transmission electron microscope (STEM). Our theorical-experimental results elucidate the influence of gap geometry on the coupled plasmons and field concentration in doped IO nanostructures, and further suggest exciting applications in plasmonic sensing and surface-enhanced spectroscopies.

This video was recorded for SPIE Photonics West 2022

Ultrafast pump-probe spectroscopy was applied to measure several fundamental material parameters in β-Ga2O3. These include times for the hole self-trapping into a polaron state, electron-phonon scattering, and energy of the lowest conduction band side valley. These different parameters were assessed by using spectrally tuneable pump and probe pulses at proper wavelengths. The obtained 300 K scattering times are 0.5 ps for the hole self-trapping, 4.5 fs for the electron-polar optical phonon scattering, and 80 fs for scattering to and from the side valley. The energy of the lowest side valley in the conduction band is 2.6 eV.

Potential applications for gallium oxide, up until now, have far exceeded our ability to scale up production. As one crucial example, gallium oxide as a material in cube satellites has been shown to provide superior climate modeling in the ozone layer. Gallium oxide’s wide bandgap and other favorable properties make it an ideal material for space-based applications. However, scaling gallium oxide production will require innovative methods to reduce defect density. AI analysis of process and optical inspection data, from substrate to device packaging, will allow manufacturers to assign causality to defects and adaptively control the production process to improve quality.

We investigate the specifics of trigonal materials and their heterostructures, in particular alpha-phase (corundum phase) alumina and gallia and their alloy alpha-(Al,Ga)2O3. Compared to more common hexagonal semiconductor materials (like group-III nitrides), the symmetry is reduced. Regarding the elastic properties, this leads to the occurrence of shear strains in heteroepitaxy and a difference between a- and m-planes. Particular care must be taken when evaluating Raman scattering for the determination of the Raman tensor; for thin films, also the thickness must be taken into account. Also results on electrical properties will be given.

Monoclinic β-Ga2O3 nanowires were fabricated using chemical vapor deposition and doped with nitrogen using remote plasma. The monoclinic phase and high crystallinity of the nanowires were confirmed by XRD and TEM, while nitrogen incorporation into the nanowires was confirmed by X-ray absorption and Raman spectroscopies. Temperature-resolved cathodoluminescence characterisation revealed a green luminescence band at 2.5 eV due to the N incorporation. The UV emission at 3.4 eV associated with self-trapped holes and its temperature-dependant behaviour were found to be identical for the undoped and N-doped nanowires. The experimental findings will be discussed in context of theoretical calculations for N-doped Ga2O3.

We present measurement protocols of performances, test and calibrations of new compact solid-state photodetectors based on β-Ga2O3 oxides, and optimized for the UVC. They present reduced dark currents, permitting room temperature operation suppressing need for a cooling system (mass and power savings) and avoiding cold surfaces that traps environmental contamination. Detectors' response peak around 215-220 nm with a bandpass of 30 nm, allowing to observe the UVC wavelength band responsible of ozone creation in the stratosphere (Herzberg continuum, 200-242 nm) and to achieve solar-blindness for wavelengths above 250 nm. Other key assets of β-Ga2O3 detectors are their radiation hard properties (longer lifetime), and possible sensitivity (several hundreds mA/W at -5 V) that allows operation at lower voltages (reduced power), a key asset for Space applications. These detectors, evaluated, tested and calibrated, will be integrated on the INSPIRE-7 nanosatellite to be launched in 2023.

In this presentation, we discuss the integration of amorphous GaOx into back-gated transistors. The a-GaOx films (22 -100 nm) were grown by plasma-enhanced atomic layer deposition (PE-ALD). The conductivity of the films was tuned by changing the O2 plasma exposure time during the ALD cycles, which determines the content in oxygen vacancies. Back-gated transistors were fabricated with Al2O3 gate oxide on highly-doped Si substrate, with or without encapsulation of the top surface. The electrical properties of the devices will be discussed. Low sub-threshold swing (~150 mV/dec), on/off ratio >105 and operating drain voltage below 5V were obtained.

β-Ga2O3 epitaxy from metal-organic chemical vapor deposition (MOCVD) has exhibited low background defects and high mobility which are promising for high-power devices. Vertical field-plate Schottky diodes have been fabricated using MOCVD β-Ga2O3 epitaxy that showed punch through breakdown with a specific on-resistance (Ron,sp) of 0.67 mΩ-cm2. This Ron,sp is among the lowest of comparable β-Ga2O3 drift layer thickness reports and can be contributed from the high-mobility MOCVD β-Ga2O3 epitaxy. We also demonstrated Pseudo vertical diodes fabricated on a thicker MOCVD β-Ga2O3 on Fe-doped substrate that showed higher voltage, better leakage current, and improved surface properties compared to the thinner films on Sn-doped substrate epitaxy.

We present κ-Ga2O3 layers grown by tin-assisted PLD on highly conductive Al-doped ZnO back contact layers. κ-Ga2O3 deposited on c-sapphire typically exhibits no lateral current flow. Significant currents can only be detected when a vertical current flow through the κ-Ga2O3 layer is enabled by the back contact confirming a strong conductivity anisotropy possibly due to suppressed transport across rotational domain boundaries. Pt/PtOx or Pd/PdOx Schottky contacts and NiO or ZnCo2O4 p-type contacts exhibit rectification ratios up to seven orders of magnitude. Further, we obtain a mean barrier height of ~2.1 eV and ideality factors as low as ~1.3 for Pt/PtOx/κ-Ga2O3 Schottky barrier diodes.

We will report on the following key recent advances in MOVCD growth and device demonstration based on homoepitaxial 010-oriented beta gallium Oxide thin films and heterostructures- (i) expanded MOCVD growth window with high quality films grown at a substrate temperature as low as 600 C, (ii) record ohmic contact specific resistance and regrown ohmic contacts using low temperature epitaxy, (iii) sharp doping profiles leading to demonstration of pure 2DEG using MOCVD-grown aluminum gallium oxide/gallium oxide heterojunctions, (iv) high quality in-situ semiconductor/dielectric interfaces grown using MOCVD, (v) a figure of merit of 355 MW/cm2 with a breakdown voltage of 2.44 kV in a β- Ga2O3 MESFET, and (vi) lateral breakdown voltages as high as 4.5 kV in a gate pad connected field plated MESFET. The low temperature epitaxy and processing approach also enables growth and fabrication of transistors on engineered composite substrates for thermal management.

We propose a novel exchange correlation potential[1] for DFT investigations of semiconductor materials, based on physical properties of the underlying microscopic screening. We demonstrate that it reproduces the low temperature band gap of several materials. Moreover, on the example of defects in semiconductors, it respects the required linearity condition of the total energy with the fractional occupation number, as expressed by the generalized Koopman’s theorem. It is shown, that alloys can be treated with a common choice of the functional. We also show that this novel functional can be used as a kernel in linear response TDDFT to reproduce excitonic effects in optical spectra.

We propose to explore tandem junctions associating single crystalline silicon bottom cell (Eg = 1.12 eV) and wide bandgap (1.7 eV) CuIn0.75Ga0.25S2 (pure-sulfide CIGSu) top cell, using GaP intermediate layer. Our purpose is to grow CIGSu films under epitaxial conditions on GaP/Si(001) to improve the top cell efficiency, thanks to a reduction of the structural defects density detrimental for the cell performance, so that CIGSu/Si tandem cells can emerge as cost competitive for the next generation of PV modules. Record efficiency on standard AZO/ZnMgO/CdS/CIGSu/Mo/Glass solar cell and epitaxy of CIGSsu on GaP/Si are demonstrated.

Chromogenic materials exhibit tunable properties as a consequence of an external stimulus such as light (photochromism), temperature (thermochromism) or potential (electrochromism..). Those smart compounds find applications in buildings and automobile industry by controlling light and heat transfer through windows for transmissive devices while colour changes in reflective devices offer great interest in the field of displays and printed electronics. Among various oxides, vanadium oxides plays a peculiar role as they adopt a specific property in respect of their stoichiometry, namely thermochromism for VO2 and electrochromism for V2O5. Comparing thin films of few hundred nanometers by RF sputtering method or thick films of few micrometers, specific attention will be devoted to the role of dopants. For instance easy tuning of the transition temperature down to RT and up to 130°C will be reported for Nb and Fe doped VO2 respectively while Mo-doping improves EC properties.

This presentation focuses on structure property/relationships in advanced materials, emphasizing multifunctional systems that exhibit multiple functionalities. Such systems are then used as building blocks for the fabrication of various emerging technologies. In particular, nanostructured materials synthesized via the bottom–up approach present an opportunity for future generation low cost manufacturing of devices [1]. We focus in particular on recent developments in solar technologies that aim to address the energy challenge, including third generation photovoltaics, solar hydrogen production, luminescent solar concentrators and other optoelectronic devices. [2-40]. References [1] J. Phys. Cond. Matt. 16, S1373 (2004); [2] Adv. Mater. 22, 1741 (2010); [3] J. Am. Chem. Soc. 132, 8868 (2010); [4] Adv. Mater. 23, 1724 (2011); [5] Appl. Phys. Lett. 98, 202902 (2011); [6] Chem. Comm. 48, 8009 (2012); [7] Adv. Func. Mater. 22, 3914 (2012); [8] Nanoscale 4, 5588 (2012); [9] Nanoscale 5, 873 (2013); [10] J. Power Sources 233, 93 (2013); [11] Chem. Comm. 49, 5856 (2013); [12] J. Phys. Chem. C 117, 14510 (2013); [13] Nature Phot. 9, 61 (2015); [14] Nanoscale 8, 3237 (2016); [15] Nano Energy 27, 265 (2016); [16] Small 12, 3888 (2016); [17] Nanotechnology 27, 215402 (2016); [18] J. Mater. Chem. C 4, 3555 (2016); [19] Sci. Rep. 6, 23312 (2016); [20] Adv. En. Mater. 6, 1501913 (2016); [21] Nanoscale 8, 4217 (2016); [22] Adv. Sci. 3, 1500345 (2016); [23] Small 11, 5741 (2015); [24] Small 11, 4018 (2015); [25] J. Mater. Chem. A 3, 2580 (2015); [26] Nano Energy 34, 214 (2017); [27] Nano Energy 35, 92 (2017); [28] Adv. Func. Mater. 27, 1401468 (2017); [29] Adv. En. Mater. 8, 1701432 (2018); [30] Chem 3, 229 (2017); [31] J. Chakrabartty et al., Nature Phot. 12, 271 (2018); [32] Nano Energy 55, 377 (2019); [33] Nanoscale Horiz. 4, 404 (2019); [34] Appl. Cat. B 250, 234 (2019); Adv. Func. Mater. 29, 1904501 (2019); [35] ACS Photonics 6, 2479 (2019); [36] Appl. Cat. B 264, 118526 (2020); [37] Adv. Func. Mater. 30, 1908467 (2020); [38] J. Mater. Chem. A 8, 20698 (2020); [39] Nano Energy 79, 105416 (2021); [40] Nano Energy 81, 105626 (2021).

Recently, transparent conducting oxides such as indium tin oxide and aluminum-doped zinc oxide have been characterized in their epsilon-near-zero crossover regions due to their strong enhancement of light-matter interaction. A newer technique, known as beam deflection, can be used to enable single-detector measurements that characterizes the complex nonlinear refractive index by detecting the angular deflection and transmission of a probe beam. Here we describe two key nonidealities in beam deflection measurements, 1) the spatio-temporal interaction of the beams with a finite relative angular separation, 2) the apparent angular deviation occurring due to strong spatially non-uniform absorption.

We report on the binding energy of a charged exciton (trion) confined in a single, epitaxially grown 1.7nm thick ZnO/(Zn,Mg)O quantum well as large as 22 meV or 27.6 meV when determined in micro-photoluminescence or transmission measurements, respectively. The attribution of the lines is further confirmed by the magnetic field dependences of the emission intensity. Charged exciton emission is found to persist up to near room temperature. The QW width was determined from high resolution transmission electron microscopy measurements. The binding energy comparable to thermal energy at room temperature is promising for trion based spintronic and optoelectronic applications.

We have fabricated a novel type of ultracompact spectrometer without dispersive element(s) suitable for the use in smartphones. It comprises a waveguide with a linear photodetector array on top. The photosensitive layer features a steep chemical concentration gradient, fabricated from (MgxZn1-x)O, allowing for spectral detection in the UV. The dimensions of the device make it ultracompact with a volume of less than 1 cubic millimeter.

Micro/Nano LED is one of hot topics for the next generation of display beyond OLED. GaN-based and Phosphide-based LEDs show terribly low emission efficiencies as the chip size gets smaller like <10. Therefore, current LED technology can’t provide efficient micro/nano LEDs suitable for VR/AR/MR display applications. We will introduce a revolutionary light emitting device, called Hybrid LED, in the presentation. Hybrid LED is composed of ZnO-based Oxide semiconductors and GaN-based Nitride semiconductors. Hybrid LED is a breakthrough for micro-LED display because its emission efficiency is constantly good enough for 5,000+ PPI display without affected by chip size unlike conventional Nitride-based and Phosphide-based LEDs. After brief discussion and review on Physical properties of Hybrid LEDs, commercial Hybrid LEDs in different colors (from blue to red) and chip sizes (a few to hundred microns) will be demonstrated to show how outstanding Hybrid LEDs are, compared with typical commercial GaN LEDs.

We investigate α-(Al_xGa_1-x)₂O₃ layers deposited by PLD for 0≤x≤1 on a- and m-plane sapphire. RSM measurements reveal a fundamental difference for these planes. Pseudomorphic α-(Al_xGa_1-x)₂O₃ on m-plane sapphire shows a shear strain e'5 along the c-axis vanishing on a-plane sapphire. Similarly, only relaxed m-plane α-(Al_xGa_1-x)₂O₃ exhibits a global lattice tilt in c-axis direction. Modeling of lattice constants and e'5 as function of x prove the shear strain to be due to the non-vanishing C14 component of the stress-strain tensor for α-(Al_xGa_1-x)₂O₃ contributing only for the m-plane. We further explain the occurrence of the lattice tilt and identify possible relaxation mechanisms.