Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B41: Defects in Gallium OxideFocus
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Sponsoring Units: DMP Chair: Jorge Munoz, University of Texas at El Paso Room: Room 319 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B41.00001: Controlling doping in Ga2O3 and AlGaO3 alloys Invited Speaker: Chris G Van de Walle The properties of gallium oxide make it particularly suitable for applications in power electronics. Ga2O3 has a large band gap (4.8 eV) but can also be highly n-type doped. Control of doping is crucial for devices: it should be possible to control the carrier concentrations all the way from semi-insulating to highly conductive n-type material. In addition, doping of AlGaO3 alloys is required for the modulation-doped heterostructures used in devices. First-principles modeling, using advanced hybrid functional calculations within density functional theory, can greatly help in resolving experimental puzzles and guiding optimal doping conditions. I will present comprehensive first-principles studies of dopant impurities and of point defects and unintentional impurities that can act as compensating centers. Compensation of n-type doping may occur due to the formation of gallium vacancies, which have an unusual split-vacancy structure [1,2]. In (AlxGa1-x)2O3 alloys, controlled doping at low concentrations has proven difficult, and native-defect compensation and DX-center formation limit doping at higher Al concentrations. I will particularly focus on the role of unintentional carbon and hydrogen impurities, which are unavoidably present during growth by chemical vapor deposition [3]. Device structures also require semi-insulating layers, in which the Fermi level is pinned far from the band edges. I will discuss how this can be implemented by doping with Mg or N dopants [4]. Diffusion of these dopants during growth or subsequent processing is a major problem, which requires detailed understanding and control of point defects. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B41.00002: Alloys of orthorhombic Ga2O3, Al2O3 , and In2O3 Hartwin Peelaers, Sierra C Seacat, John L Lyons Ga2O3 is a wide-bandgap semiconductor with promising applications in high-power devices and UV photodetectors. Monoclinic β-gallia is its thermodynamically stable phase, but other polymorphs can be stabilized. Of particular interest is the orthorhombic κ-polymorph, as it possesses ferroelectric properties and exhibits large spontaneous electrical polarizations. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B41.00003: Role of lattice vibrations in gallium vacancy formation in monoclinic Ga2O3 Sai Mu, Mark E Turiansky, Chris G Van de Walle Gallium vacancies (VGa) play a pivotal role in carrier compensation in n-type Ga2O3. Previous theoretical investigations of VGa formation energies and charge-state transition levels were limited to zero temperature. We investigate the effect of lattice vibrations on the defect formation energy of VGa, its charge-state transition levels, and band renormalization in monoclinic Ga2O3 at finite temperatures. Using hybrid density functional calculations, the formation energy and charge-state transition levels of four different VGa configurations [VGa(I), VGa(II), VGaib, VGaic] are calculated. The lattice vibrations and their contribution to the free energy are assessed using the generalized gradient approximation. Although the VGaib configuration of the split vacancy is less favorable than the VGaic configuration at zero temperature, lattice vibrations are found to stabilize VGaib over VGaic at high temperature. All studied charge-state transition levels exhibit a blue shift at elevated temperature; the impact of this shift on the electron capture process will be discussed. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B41.00004: Transition metals as shallow donors in Ga2O3 Siavash Karbasizadeh, Sai Mu, Chris G Van de Walle We present an in-depth investigation of transition-metal impurities as shallow donors in monoclinic |
Monday, March 6, 2023 12:42PM - 12:54PM |
B41.00005: Atomic-displacement threshold energies and defect generation in irradiated β-Ga2O3 : a first-principles investigation Blair Tuttle, Nathaniel Karom, Andrew O'Hara, Ronald D Schrimpf, Sokrates T Pantelides Gallium oxide is an emerging wide-band-gap semiconductor with promise for applications in space systems that may be exposed to energetic particles. We use molecular dynamics simulations, based on first principles density-functional methods, to determine the nature and stability of the defects generated by atoms knocked-out by particle irradiation at near threshold energies (found to be for Ga and for O). For Ga atoms, several types of low energy knock-out events result in defect complexes, but the final structures depend critically on the initial displacement direction. In contrast, a vacancy plus a peroxide linkage occurs in all types of low energy knock-out events of O atoms. Based on energy-barrier calculations there is a low (high) probability for Ga (O) defect recombination. The electronic structure of residual, relaxed defects generated by Ga knock-outs reveals defect levels near the band edges. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B41.00006: Defect and Dopant Characterization using Terahertz Electron Paramagnetic Resonance Ellipsometry: Fe in Ga2O3 Mathias M Schubert, Rafal Korlacki, Steffen Richter, Sean Knight, Philipp Kuehne, Vallery Stanishev, Megan Stokey, Zbigniew Galazka, Klaus Irmscher, Vanya Darakchieva The control over electrical conductivity is critical key to enablingultrawide bandgap materials, e.g., for high power electronic devices. Identifying defects and their electronic properties remains a challenge. Here, we introduce frequency-domain Terahertz Electron ParamagneticResonance (EPR) ellipsometry as a new fully polarization-resolving spectroscopy tool to study defects in semiconductors thin films and heterostructures at very high magnetic fields and very high frequencies. We determine the full spectral and magnetic polarization response of EPR signals as a continuous function of both field and frequency. THz EPR ellipsometry is shown previously for the nitrogen defect in SiC. Here, we investigate Fe-doped gallium oxide single crystals, and detect rich spin signatures which strongly vary with crystal orientation, frequency, and field. The neutral defect Fe3+ is a high-spin system with s=5/2 and large zero-field splitting. Iron canincorporate at either Ga site but appears preferentially in octahedral configuration. Different claims exist about the nature of the spin Hamiltonian and approximate values for simplified orthorhombicmodels have been reported. We obtain the anisotropic g-factor as well as the zero-field Hamiltonian up to fourth order which allows to discuss the relevance of the monoclinic character of the local site symmetry. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B41.00007: Uniform and controlled Si doping of Ga2O3 by disilane via hybrid molecular beam epitaxy Zhuoqun Wen, Elaheh Ahmadi, Kamruzzaman Khan β-Ga2O3 has attracted a great deal of interest in recent years due to its ultra-wide bandgap (Eg = 4.7eV) and the availability of large-scale substrates. n-type doping of Ga2O3 has been achieved using Sn, Si, and Ge by metal-organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), and molecular beam epitaxy (MBE). Regardless, in conventional MBE systems, achieving Si-doped Ga2O3 films with wide-ranging doping concentrations and uniform doping profiles has been challenging due to the oxidation of solid Si source in the oxygen-rich environment. Recently, J. P. McCandless et al. reached to low 1017 cm-3 Si doping concentration by inserting an endplate into the Si crucible. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B41.00008: Hydrogen as a probe of VGa(2) in β-Ga2O3 Amanda Portoff, Andrew B Venzie, Michael B Stavola, W. Beall Fowler, Stephen J Pearton, Evan R Glaser While a number of O-H and O-D lines have been observed for hydrogen and deuterium in β-Ga2O3, it has been commonly reported that there is no absorption for the polarization E//[010] [1,2]. This experimental result has led to O-H and O-D defect structures that involve shifted configurations of a vancancy at the tetrahedrally coordinated Ga(1) site and have ruled out structures that involve a vacancy at the octahedrally coordinated Ga(2) site because these structures are predicted to show absorption for E//[010] [1,2]. Weak O-D lines at 2475 and 2493 cm-1 with components of their polarization with E//[010] have been discovered for β-Ga2O3 annealed in a D2 ambient and are discussed here. O-D defect structures involving a VGa(2) are proposed for these centers and an estimate is made for a lower limit of the concentration of VGa(2) in the samples from the intensities of the IR absorption lines. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B41.00009: H trapping at the metastable cation vacancy in α-Ga2O3 and α-Al2O3 Andrew B Venzie, Amanda Portoff, Michael B Stavola, W B Fowler, Stephen J Pearton α-Ga2O3 has the corundum structure analogous to that of α-Al2O3 [1]. The O-H and O-D centers produced by the implantation of H+ and D+ into α-Ga2O3 have been studied by infrared spectroscopy and complementary theory [2]. An O-H line at 3269 cm-1 is assigned to H complexed with a Ga vacancy (VGa), similar to the case of H trapped by an Al vacancy (VAl) in α- Al2O3. The isolated VGa and VAl defects in α-Ga2O3 and α-Al2O3 are found by theory to have a “shifted” vacancy-interstitial-vacancy equilibrium configuration, similar to VGa in β-Ga2O3 which also has shifted structures [3-5]. However, the addition of H causes the complex with H trapped at an unshifted vacancy to have lowest energy in both α-Ga2O3 and α-Al2O3. (α-Ga2O3 samples were grown at the Korean Institute of Ceramic Engineering and Technology [6].) |
Monday, March 6, 2023 1:42PM - 1:54PM |
B41.00010: Effect of electric field on the Ovac in low dimensional β-Ga2O3 for non-volatile memory application Chandrasekar Sivakumar, Mon-Shu Ho Several decades have been devoted to the development of a scalable universal memory cell capable of combining the speed of DRAM with the nonvolatility of FLASH memory. Resistive-switching random access memory (ReRAM) is one of the prospective non-volatile technologies that is often investigated by researchers. Some of the key benefits of ReRAM are scaling possibilities, low-power operation, high-speed, and compatibility with existing CMOS technologies. Although the scientific community has thoroughly researched dielectric thin films as resistive switching materials, the viability of low-dimensional (LD) materials has received little attention. For many decades, beta phase gallium oxide (β-Ga2O3) has been researched as a prospective candidate for numerous semiconductor device applications. The oxygen vacancy in the metal oxide ReRAM is the most important aspect of switching in the dielectric switching material; thus, it is essential to examine their reaction to the electric field for future advancements. The purpose of this study is to conduct a theoretical and experimental assessment of the RS phenomena in planar and vertical LD: β-Ga2O3 nanostructures. The LD: β-Ga2O3resistive memory devices were experimentally verified using VLS-grown nanostructures. Physical and chemical characterizations of the as-grown nanostructures confirmed the existence of spontaneous defects, including oxygen vacancies. Meanwhile, the underlying physical and electrical characteristics of comparable structures corresponding with the DFT framework have been modeled through the QuantumATK package. And the effect of electric field in the planar and vertical device structure on the oxygen vacancies in the LD: β-Ga2O3 is reported through the electrical characteristics. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B41.00011: Chip-Scale Electron Spin Resonance Spectroscopy of Spin-Active Defects in Epitaxial β-Ga2O3 Arjan Singh, Jimy Encomendero, Felix V Hensling, Kathy Azizie, Vladimir Protasenko, Kazuki Nomoto, Darrell G Schlom, Debdeep Jena, Huili Grace Xing, Farhan Rana We demonstrate the use of a chip-scale, coplanar waveguide resonator in temperature-dependent Electron Spin Resonance (ESR) spectroscopy of defects in the ultra-wide bandgap semiconductor β-Ga2O3. The study of point defects in β-Ga2O3, many of which are spin active, is essential to establish it as a material platform for high-power electronics. Further, ESR spectroscopy has been a useful tool in the study of defects in semiconductors owing to its sensitivity to a low density of spin-active defects, its ability to readily differentiate between various defect charge states, and to discern asymmetries in the defects’ environment by extracting the associated g-tensor. However, commercially available ESR spectrometers utilize bulky cavity resonators which are not sensitive to a low density of spin-defects in sub-micron epitaxial thin-films, at interfaces, or on surfaces due to the resonator’s mode volume being much larger than the region being probed. The two-dimensional nature of our high-Q resonator allows us to overcome this limitation. We present results on the nature of defects in micron and sub-micron epitaxial β-Ga2O3. Our measurements show the presence of additional defect signatures in epitaxial β-Ga2O3 beyond those that can be observed by commercial X-Band spectrometers. We will discuss the characteristics and possible sources of these additional signatures, as well as the wider applicability of our chip-scale ESR technique in probing spin defects in semiconductor thin films, interfaces, and surfaces. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B41.00012: Self-Trapped Hole in Ultra Wide Bandgap β-Ga2O3 Films; Its Temperature Dependent Luminescences Isiaka O Lukman, Leah Bergman
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