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1. Hydrogen centers as a probe of VGa(2) defects in β -Ga2O3

   https://doi.org/10.1063/5.0138904  

   Portoff, Amanda ; Stavola, Michael ; Fowler, W. Beall ; Pearton, Stephen J. ; Glaser, Evan R. ( February 2023 , Applied Physics Letters)

   While a number of O-H and O-D vibrational lines have been observed for hydrogen and deuterium in β-Ga2O3, it has been commonly reported that there is no absorption with a component of the polarization E parallel to the [010], or b, axis. This experimental result has led to O-H defect structures that involve shifted configurations of a vacancy at the tetrahedrally coordinated Ga(1) site [VGa(1)] and have ruled out structures that involve a vacancy at the octahedrally coordinated Ga(2) site [VGa(2)], because these structures are predicted to show absorption for E//[010]. In this Letter, weak O-D lines at 2475 and 2493 cm−1 with a component of their polarization with E//[010] are reported for β-Ga2O3 that had been annealed in a D2 ambient. O-D defect structures involving an unshifted VGa(2) are proposed for these centers. An estimate is made that the concentration of VGa(2) in a Czochralski-grown sample is 2–3 orders of magnitude lower than that of VGa(1) from the intensities of the IR absorption lines.

    

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2. Impurity-hydrogen complexes in β-Ga2O3: Hydrogenation of shallow donors vs deep acceptors

   Venzie, Andrew ; Portoff, Amanda ; Perez Valenzuela, E. Celeste ; Stavola, Michael ; Fowler, W. Beall ; Glaser, Evan ( January 2022 , Journal of applied physics)

   Substitutional impurities in Ga2O3 are used to make the material n-type or semi-insulating. Several O-D vibrational lines for OD-impurity complexes that involve impurities that are shallow donors and deep acceptors have been reported recently. The present paper compares and contrasts the vibrational properties of complexes that involve shallow donors (OD-Si and OD-Ge) with complexes that involve deep acceptors (OD-Fe and OD-Mg). Complementary theory investigates the microscopic structures of defects that can explain the observed vibrational properties. 

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3. Tuning electrical properties in Ga2O3 polymorphs induced with ion beams

   https://doi.org/10.1063/5.0133181  

   Polyakov, A. Y. ; Kochkova, А. I. ; Azarov, A. ; Venkatachalapathy, V. ; Miakonkikh, A. V. ; Vasilev, A. A. ; Chernykh, A. V. ; Shchemerov, I. V. ; Romanov, A. A. ; Kuznetsov, A. ; et al ( March 2023 , Journal of Applied Physics)

   Ion beam fabrication of metastable polymorphs of Ga2O3, assisted by the controllable accumulation of the disorder in the lattice, is an interesting alternative to conventional deposition techniques. However, the adjustability of the electrical properties in such films is unexplored. In this work, we investigated two strategies for tuning the electron concentration in the ion beam created metastable κ-polymorph: adding silicon donors by ion implantation and adding hydrogen via plasma treatments. Importantly, all heat treatments were limited to ≤600 °C, set by the thermal stability of the ion beam fabricated polymorph. Under these conditions, silicon doping did not change the high resistive state caused by the iron acceptors in the initial wafer and residual defects accumulated upon the implants. Conversely, treating samples in a hydrogen plasma converted the ion beam fabricated κ-polymorph to n-type, with a net donor density in the low 1012 cm−3 range and dominating deep traps near 0.6 eV below the conduction band. The mechanism explaining this n-type conductivity change may be due to hydrogen forming shallow donor complexes with gallium vacancies and/or possibly passivating a fraction of the iron acceptors responsible for the high resistivity in the initial wafers.

    

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4. Editors’ Choice—Vibrational Properties of Oxygen-Hydrogen Centers in H + - and D + -Implanted Ga 2 O 3

   https://doi.org/10.1149/2162-8777/abd458  

   Portoff, Amanda ; Venzie, Andrew ; Qin, Ying ; Stavola, Michael ; Fowler, W. Beall ; Pearton, Stephen J. ( December 2020 , ECS Journal of Solid State Science and Technology)

   The ion implantation of H⁺and D⁺into Ga₂O₃produces several O–H and O–D centers that have been investigated by vibrational spectroscopy. These defects include the dominant V_Ga(1)-2H and V_Ga(1)-2D centers studied previously along with additional defects that can be converted into this structure by thermal annealing. The polarization dependence of the spectra has also been analyzed to determine the directions of the transition moments of the defects and to provide information about defect structure. Our experimental results show that the implantation of H⁺(or D⁺) into Ga₂O₃produces two classes of defects with different polarization properties. Theory finds that these O–H (or O–D) centers are based on two shifted configurations of a Ga(1) vacancy that trap H (or D) atom(s). The interaction of V_Ga(1)-nD centers with other defects in the implanted samples has also been investigated to help explain the number of O–D lines seen and their reactions upon annealing. Hydrogenated divacancy V_Ga(1)-V_Ocenters have been considered as an example.

    

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5. Chemical dynamics study on the gas-phase reaction of the D1-silylidyne radical (SiD; X 2 Π) with deuterium sulfide (D 2 S) and hydrogen sulfide (H 2 S)

   https://doi.org/10.1039/d1cp01629f  

   Goettl, Shane J. ; Doddipatla, Srinivas ; Yang, Zhenghai ; He, Chao ; Kaiser, Ralf I. ; Silva, Mateus X. ; Galvão, Breno R. ; Millar, Tom J. ( June 2021 , Physical Chemistry Chemical Physics)

   The reactions of the D1-silylidyne radical (SiD; X 2 Π) with deuterium sulfide (D 2 S; X 1 A 1 ) and hydrogen sulfide (H 2 S; X 1 A 1 ) were conducted utilizing a crossed molecular beams machine under single collision conditions. The experimental work was carried out in conjunction with electronic structure calculations. The elementary reaction commences with a barrierless addition of the D1-silylidyne radical to one of the non-bonding electron pairs of the sulfur atom of hydrogen (deuterium) sulfide followed by possible bond rotation isomerization and multiple atomic hydrogen (deuterium) migrations. Unimolecular decomposition of the reaction intermediates lead eventually to the D1-thiosilaformyl radical (DSiS) (p1) and D2-silanethione (D 2 SiS) (p3) via molecular and atomic deuterium loss channels (SiD–D 2 S system) along with the D1-thiosilaformyl radical (DSiS) (p1) and D1-silanethione (HDSiS) (p3) through molecular and atomic hydrogen ejection (SiD–H 2 S system) via indirect scattering dynamics in barrierless and overall exoergic reactions. Our study provides a look into the complex dynamics of the silicon and sulfur chemistries involving multiple deuterium/hydrogen shifts and tight exit transition states, as well as insight into silicon- and sulfur-containing molecule formation pathways in deep space. Although neither of the non-deuterated species – the thiosilaformyl radical (HSiS) and silanethione (H 2 SiS) – have been observed in the interstellar medium (ISM) thus far, astrochemical models presented here predict relative abundances in the Orion Kleinmann-Low nebula to be sufficiently high enough for detection. 

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