Ga Vacancy

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Filip Tuomisto - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Mn and Mg dopants on Vacancy defect formation in ammonothermal GaN
    Journal of Crystal Growth, 2020
    Co-Authors: T. Heikkinen, M. Zając, J. Pavlov, Tomas Ceponis, Eugenijus Gaubas, Filip Tuomisto
    Abstract:

    Abstract We have applied positron annihilation spectroscopy to study the formation of Ga Vacancy related defects in Mg and Mn doped bulk GaN crystals grown by the ammonothermal method. We show that Mn doping has little or no effect on the formation of Ga vacancies, while Mg doping strongly suppresses their formation, in spite of both dopants leading to highly resistive material. We suggest the differences are primarily due to the hydrogen-dopant interactions. Further investiGations are called for to draw a detailed picture of the atomic scale phenomena in the synthesis of ammonothermal GaN.

  • Ga vacancies and electrical compensation in β-Ga 2 O 3 thin films studied with positron annihilation spectroscopy
    Oxide-based Materials and Devices X, 2019
    Co-Authors: Filip Tuomisto, Ilja Makkonen, Antti Karjalainen, Vera Prozheeva, Günter Wagner, M. Baldini
    Abstract:

    We have applied positron annihilation spectroscopy to study Vacancy-type defects in unintentionally doped and Si and Sn doped β-Ga2O3 homoepitaxial thin films grown by metal-orGanic chemical vapor deposition (MOCVD). We detect Ga Vacancy related defects at high concentrations in semi-insulating and highly resistive material, while conductive (ntype) material exhibits very low Ga Vacancy concentrations. These findings show that Ga vacancies can act as efficient electrical compensators for n-type conductivity, but their concentrations can be suppressed by controlling the growth environment, leading to efficient n-type doping. We also note the strong anisotropy of the positron annihilation signals and give recommendation for presenting positron data obtained in β-Ga2O3.

  • Increased p-type conductivity in GaNxSb1-x, experimental and theoretical aspects
    Journal of Applied Physics, 2015
    Co-Authors: Natalie Segercrantz, Ilja Makkonen, Jonatan Slotte, Jan Kujala, Tim D. Veal, M. J. Ashwin, Filip Tuomisto
    Abstract:

    The large increase in the p-type conductivity observed when nitrogen is added to GaSb has been studied using positron annihilation spectroscopy and ab initio calculations. Doppler broadening measurements have been conducted on samples of GaN x Sb 1− x layers grown by molecular beam epitaxy, and the results have been compared with calculated first-principle results corresponding to different defect structures. From the calculated data, binding energies for nitrogen-related defects have also been estimated. Based on the results, the increase in residual hole concentration is explained by an increase in the fraction of neGative acceptor-type defects in the material. As the band Gap decreases with increasing N concentration, the ionization levels of the defects move closer to the valence band. Ga Vacancy-type defects are found to act as positron trapping defects in the material, and the ratio of Ga Vacancy-type defects to Ga antisites is found to be higher than that of the p-type bulk GaSb substrate. Beside Ga vacancies, the calculated results imply that complexes of a Ga Vacancy and nitrogen could be present in the material.

  • Vacancy-hydrogen complexes in ammonothermal GaN
    Journal of Crystal Growth, 2014
    Co-Authors: Filip Tuomisto, T. Kuittinen, M. Zając, R. Doradziński, Dariusz Wasik
    Abstract:

    Abstract We have applied positron annihilation spectroscopy to study in-grown Vacancy defects in bulk GaN crystals grown by the ammonothermal method. We observe a high concentration of Ga Vacancy related defects in n-type samples with varying free electron and oxygen content. The positron lifetimes found in these samples suggest that the Ga vacancies are complexed with hydrogen impurities. The number of hydrogen atoms in each Vacancy decreases with increasing free electron concentration and oxygen and hydrogen content. The local vibrational modes observed in infrared absorption support this conclusion.

  • Ga-Vacancy activation under low energy electron irradiation in GaN-based materials
    MRS Online Proceedings Library, 2012
    Co-Authors: Henri Nykänen, Sami Suihkonen, Lucasz Kilanski, Markku Sopanen, Filip Tuomisto
    Abstract:

    We present results on optical degradation of Gallium nitride based materials under low energy electron beam irradiation (LEEBI). GaN thin film and GaN/InGaN quantum well samples, grown by metal-orGanic vapor phase epitaxy (MOVPE), were exposed to a tightly focused (ø = 2 nm, J = 0–130 kA/cm^2), rapidly scanning electron beam (e-beam) with energy of 5–20 keV and dose of 0–500 μC/cm^2. The irradiation severely reduced the band-to-band photoluminescence of the exposed sample areas. Performing positron annihilation spectroscopy measurements on the irradiated films revealed an important increase of Ga-Vacancy concentration as a function of the irradiation dose. Based on the measurements we propose that in-grown passive V_Ga-H_ n complexes are present in MOVPE grown GaN (and its alloys), and are activated by LEEBI.

F. Sarto - One of the best experts on this subject based on the ideXlab platform.

  • the spectrum of energy levels of the Ga Vacancy deuterium complexes in p Gaas
    Journal of Applied Physics, 1993
    Co-Authors: Amore A Bonapasta, B. Bonanni, L. Cherubini, Valentina Emiliani, A. Frova, R. N. Sacks, M Capizzi, F. Sarto
    Abstract:

    Energy levels of the complexes formed by Ga vacancies binding one or more deuterium (or hydrogen) atoms are investiGated by low‐temperature photoluminescence. Since the as‐grown, nondeuterated material is unintentionally doped p type, the emission is possible because of ‘‘internal’’ recombination from a D donor in an adjacent bond‐center position and the ground levels of the different possible Vacancy configurations, with zero, one, or more D atoms trapped in its dangling bonds. At 2 K, the transitions occur at 1.14, 1.19–1.22, 1.33–1.30, and 1.34 eV, and the last two have never been observed before. The given energy ranges correspond to laser excitation increasing from the lowest to highest level, for a given D treatment of the material. We explain the new transitions and the multiplet character of some of the bands in terms of the possible different ways of accommodating the D atoms inside the Vacancy. The level separation in our data is less than that predicted theoretically for the ‘‘bare’’ Vacancy wi...

  • The spectrum of energy levels of the GaVacancy/deuterium complexes in p‐GaAs
    Journal of Applied Physics, 1993
    Co-Authors: A. Amore Bonapasta, B. Bonanni, Mario Capizzi, L. Cherubini, Valentina Emiliani, A. Frova, R. N. Sacks, F. Sarto
    Abstract:

    Energy levels of the complexes formed by Ga vacancies binding one or more deuterium (or hydrogen) atoms are investiGated by low‐temperature photoluminescence. Since the as‐grown, nondeuterated material is unintentionally doped p type, the emission is possible because of ‘‘internal’’ recombination from a D donor in an adjacent bond‐center position and the ground levels of the different possible Vacancy configurations, with zero, one, or more D atoms trapped in its dangling bonds. At 2 K, the transitions occur at 1.14, 1.19–1.22, 1.33–1.30, and 1.34 eV, and the last two have never been observed before. The given energy ranges correspond to laser excitation increasing from the lowest to highest level, for a given D treatment of the material. We explain the new transitions and the multiplet character of some of the bands in terms of the possible different ways of accommodating the D atoms inside the Vacancy. The level separation in our data is less than that predicted theoretically for the ‘‘bare’’ Vacancy wi...

  • Optical Emission Study of the Energy Levels of Ga-Vacancy/HYDROGEN Complexes in N and P-TYPE GaAs
    MRS Proceedings, 1992
    Co-Authors: A. Amore Bonapasta, B. Bonanni, Mario Capizzi, L. Cherubini, Valentina Emiliani, A. Frova, F. Sarto
    Abstract:

    ABSTRACTThe formation of Ga-Vacancy/hydrogen complexes in GaAs has been detected via photoluminescence measurements. Different degrees of hydrogénation can be achieved by low-energy H- or D-ion irradiation from a Kaufman source. The volume incorporation, for equal treatment, is dependent upon the density of impurities and defects where H can bind. In originally p-type MBE-GaAs, prolonged hydrogen treatments lead to the appearance of three emission structures in the range 1.15–1.34 eV. The results are explained in terms of transitions to different states of charge of Gallium vacancies trapping one or more H-atoms, the activity of the individual states being dependent upon the H-dose and the nature of the laser excitation. The model is supported by comparison with the changes in the Ga-Vacancy/donor emission band in degenerate n-type samples, as it evolves, from the virgin condition, through hydrogenation. The present observation provides also valid support to the creation, in p-type material, of a semi-shallow donor associated to H trapped along the As-Ga bond, in the immediate neighborhood of the Gallium Vacancy.

Kimmo Saarinen - One of the best experts on this subject based on the ideXlab platform.

  • Dominant intrinsic acceptors in GaN and ZnO
    Physica Scripta, 2006
    Co-Authors: Kimmo Saarinen, S. Hautakangas, Filip Tuomisto
    Abstract:

    Positron annihilation measurements reveal neGatively charged Ga vacancies in n-type GaN and Zn vacancies in n-type ZnO. Positron trapping at other neGative defects is not observed, indicating that cation vacancies are the dominant acceptors in these materials. The Vacancy concentrations are the same as the total acceptor densities determined in Hall experiments, confirming the dominant role of the Vacancy defects. The Ga Vacancy in GaN is found as the main compensating centre over the range of four orders of magnitude of intentional oxygen doping.

  • Direct evidence of impurity decoration of Ga vacancies in GaN from positron annihilation spectroscopy
    Physical Review B, 2006
    Co-Authors: S. Hautakangas, Martti J. Puska, Ilja Makkonen, V. Ranki, Kimmo Saarinen, David C. Look
    Abstract:

    Positron annihilation spectroscopy, supported by ab initio theory, has been applied to verify the decoration of Ga vacancies in $\mathrm{GaN}$ by oxygen and hydrogen. Our results indicate that the Doppler broadening measurement of electron momentum distribution is sensitive enough to distinguish even between N and O atoms neighboring the Ga Vacancy. We identify isolated ${V}_{\mathrm{Ga}}$ in electron irradiated $\mathrm{GaN}$ and ${V}_{\mathrm{Ga}}\text{\ensuremath{-}}{\mathrm{O}}_{\mathrm{N}}$ complexes in highly O-doped high-purity $\mathrm{GaN}$. Evidence of H decoration of Ga vacancies is obtained in epitaxial $\mathrm{GaN}$ grown by metalorGanic chemical-vapor deposition.

  • Dissociation of VGa–ON complexes in HVPE GaN by high pressure and high temperature annealing
    physica status solidi (b), 2006
    Co-Authors: Filip Tuomisto, Martti J. Puska, S. Hautakangas, Ilja Makkonen, V. Ranki, Kimmo Saarinen, Michal Bockowski, Tadeusz Suski, Tanya Paskova, Bo Monemar
    Abstract:

    We have used positron annihilation spectroscopy to study the high-pressure annealing induced thermal recovery of Vacancy defects in free-standing GaN grown by hydride vapor phase epitaxy (HVPE). The results show that the in-grown Ga Vacancy complexes recover after annealing at 1500-1700 K. Comparison of the experimental positron data with ab-initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga Vacancy. We show that the difference between the isolated V Ga in electron irradiated GaN and the V Ga -O N complexes in highly O-doped GaN is clear, and the Ga Vacancy related defect complexes that start dissociating at 1500 K can be identified as V Ga -O N pairs.

  • Donor-acceptor pair emission enhancement in mass-transport-grown GaN
    Journal of Applied Physics, 2005
    Co-Authors: Tanja Paskova, S. Hautakangas, Kimmo Saarinen, B. Arnaudov, Plamen Paskov, Ewa M. Goldys, Ulf Södervall, Bo Monemar
    Abstract:

    A dominating donor-acceptor pair (DAP) emission at about 3.27 eV is observed in the photoluminescence and cathodoluminescence spectra of intentionally undoped mass-transport (MT)-grown GaN, while only a weak presence of the DAP emission is recorded in the as-grown hydride vapor phase epitaxial GaN. A comparative study of impurity and native defect incorporation in the as-grown and MT GaN was performed, showing a significant increase of oxygen and empty clusters involving Ga Vacancy and oxygen in the MT GaN. Based on the observed results as well as on doping analysis of the structure and kinetic analysis of the emission intensities, we propose an acceptorlike complex, creating a state as a semiclassical potential well near the valence-band top due to the local tensile strain caused by the empty clusters to be responsible for the dominating behavior of the DAP emission.

  • Observation of defect complexes containing Ga vacancies in GaAsN
    Applied Physics Letters, 2003
    Co-Authors: Juha Toivonen, Markku Sopanen, Teppo Hakkarainen, Harri Lipsanen, J. Oila, Kimmo Saarinen
    Abstract:

    Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers were found to contain Ga vacancies in defect complexes. The density of the Vacancy complexes increases rapidly to the order of 1018 cm−3 with increasing N composition and decreases after annealing at 700 °C. The anticorrelation of the Vacancy concentration and the integrated photoluminescence intensity suggests that the Ga Vacancy complexes act as nonradiative recombination centers.

R. C. Newman - One of the best experts on this subject based on the ideXlab platform.

  • Observation of Ga vacancies in silicon δ-doping superlattices in (001) GaAs
    Applied Physics Letters, 1997
    Co-Authors: T. Laine, Kimmo Saarinen, M. J. Ashwin, J. Mäkinen, P. Hautojärvi, C. Corbel, R. C. Newman
    Abstract:

    Positron annihilation experiments have been performed to investiGate the compensating defects in silicon δ-doping superlattices in (001) GaAs. The results reveal vacancies and ion-type defects, which are located between the delta planes in undoped GaAs. The Vacancy defect is identified as the Ga Vacancy and the neGative ion is attributed to the Ga antisite. The concentrations of these defects increase strongly, when the areal concentrations of free carriers are reduced at the delta planes.

  • the lattice locations of silicon impurities in Gaas effects due to stoichiometry the fermi energy the solubility limit and dx behaviour
    Semiconductor Science and Technology, 1994
    Co-Authors: R. C. Newman
    Abstract:

    An outline of infrared localized vibrational mode absorption spectroscopy relevant to silicon impurities in GaAs is presented. Absorption lines from SiGa donors, SiAs acceptors, SiGa-SiAs pairs, SiGa-VGa (Ga Vacancy) pairs and a complex Si-X (involving SiAs and VGa) have been identified as well as lines from SiGa-CuGa, SiGa-H, SiAs H and SiGa-BAs pairs. These observations are related to the electrical properties of n-type Bridgman, liquid-encapsulated Czochralski and molecular beam epitaxial (MBE) (001) GaAs, and to p-type liquid phase epitaxial and MBE (111)A layers. The discussion relates to dynamic site switching, effects due to counter-doping with shallow acceptors, the solubility of silicon, and DX behaviour observed in homogeneously doped material and proposed for delta -doped MBE (001) layers. The major problem is to understand the processes that limit the maximum carrier concentration that can be achieved in n-type crystals.

Yan Meng - One of the best experts on this subject based on the ideXlab platform.

  • The important role of Ga vacancies in the ferromagnetic GaN thin films
    Journal of Alloys and Compounds, 2017
    Co-Authors: Xingguo Gao, Baoyuan Man, Chao Zhang, Jiancai Leng, Qiang Wang, Meina Zhang, Yan Meng
    Abstract:

    Abstract Room-temperature ferromagnetism was observed in the unintentionally doped GaN films, which were fabricated using laser molecular beam epitaxy followed by annealing process at different temperatures from 800 to 1000 °C for 25 min in flowing nitrogen Gas. The annealing temperature has a prominent effect on the crystalline quality, the surface morphology, the concentration of Ga vacancies and the magnetic properties of the GaN films. It is found that high temperature annealing process is an effective means of introducing Ga vacancies, which play an important role in the origin of room-temperature ferromagnetism in the GaN samples. The Ga Vacancy-related ferromagnetism may be an assistant mechanism in the Mn-doped GaN films, but it is dominant in the unintentionally doped GaN films, which deserves further study to develop novel diluted magnetic semiconductors without dopants.