Growth and optical waveguide fabrication in spinel MgGa2O4 crystal

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Abstract

We report on optical waveguide fabrication in a spinel MgGa2O4 crystal by 6.0 MeV carbon ion implantation at a fluence of 2 × 1015 ions/cm2 for the first time to our knowledge. The MgGa2O4 crystal was grown by the floating zone method. The refractive index profile reconstructed by reflectivity calculation method showed that the MgGa2O4 waveguide is a typical barrier waveguide. The typical barrier-shaped refractive index profile is attributed mainly to the nuclear energy deposition of the incident carbon ions into the MgGa2O4 crystal. By performing end-coupling measurements and using the beam propagation method (BPM) for the analysis of the observed modes, it can be concluded that the modes can be confined inside the waveguide.

Introduction

Transparent semiconducting oxides (TSOs) with wide bandgap can be used for various electronic and optoelectronic applications, such as light emitting diodes, Schottky diodes and high temperature gas sensors. Magnesium gallate (MgGa2O4) as a new wide bandgap transparent semiconducting oxide, has remarkable properties, including high melting point, chemical resistance and low electrical losses. Many reports have already been published on the study of MgGa2O4 polycrystalline and nanocrystaline materials [1], [2], [3]. Single crystals of MgGa2O4 have been grown from PbO-PbF2 solutions [4], and from the melt by the Czochralski, Bridgman and Kyropoulos techniques [5], [6]. A Ni doped MgGa2O4 single crystal was grown by the floating zone method for tunable laser application [7]. In this work, a high quality MgGa2O4 spinel crystal was successfully grown by the floating zone method, which is a crucible-free method [8].

Ion implantation is a well established process, which can be applied for selective area doping [9], nanoclusters [10], [11] and waveguide fabrication [12], [13], [14], [15], [16]. Ion implantation induced radiation damage is caused by the displacement of lattice atoms and excitation and ionisation of target atoms [17], [18]. Enhanced irradiation tolerance in nanocrystalline MgGa2O4 by Kr ion irradiation was reported by Shen et al. [3]. Bacorisen et al. reported that in the half-inverse spinel MgGa2O4, a core damage region, which consists of a partial rearrangement of atoms to the normal spinel structure, is formed after 10 keV cascades [19]. Ion implantation, which can superiorly modify the refractive index profile of materials, has been widely applied to fabricate optical waveguides [20], [21], [22]. A planar optical waveguide in magnesium spinel oxide (MgAl2O4) crystal was fabricated using 6.0 MeV oxygen ion implantation at a fluence of 1.5 × 1015 ions/cm2 [23]. The remarkable properties of MgGa2O4 spinel crystal drew huge attention for developing optical waveguides in it.

In this paper, we report, to our knowledge for the first time, on the characterization of an MgGa2O4 waveguide fabricated by 6.0 MeV carbon ion implantation. The main purposes of this work are first, to provide the solid phase reaction and XRD pattern of MgGa2O4 single crystals; second, to show the modes, refractive index profile and near-field intensity of a MgGa2O4 optical waveguide.

Section snippets

Solid phase reaction

β-Ga2O3 and MgO powder with stoichiometric ratio of 1.2:1 was used to press into rods. The higher ratio of β-Ga2O3 is due to evaporation during the solid phase reaction and crystal growth process. The rods were pressed by a cold isostatic press under 70 MPa, and then sintered at three different temperatures, 1000 °C, 1100 °C and 1200 °C, for 8 h, respectively, to initiate the solid phase reaction forming polycrystalline MgGa2O4. As seen from the XRD spectrum shown in Fig. 1(a), at 1000 °C MgGa2O4 has

XRD pattern of powdered MgGa2O4 crystal

For investigating the crystal quality by XRD, part of the as-grown single crystal was grinded into powder. Fig. 3(a) shows the XRD pattern of the powdered MgGa2O4 single crystal. For comparison, the XRD spectrum of MgGa2O4 taken from the data base JCPDS, is given in Fig. 3(b). By comparing these two figures (Fig. 3(a) and (b)), it can be concluded that X-ray diffraction (XRD) patterns of the powdered MgGa2O4 single crystal is well matched with the JCPDS data (10-0113). No other crystal phases than

Summary

An MgGa2O4 single crystal was grown by the floating zone method. The band gap of the MgGa2O4 single crystal was estimated to be about 4.7 eV measured by optical spectroscopy. An MgGa2O4 waveguide was fabricated by 6.0 MeV carbon ion implantation at a fluence of 2 × 1015 ions/cm2. The refractive index profile indicates that the MgGa2O4 waveguide is a typical barrier waveguide. The barrier is formed mainly due to the nuclear energy deposition of the incident carbon ions during ion implantation, which

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 11405073), the State Key Laboratory of Nuclear Physics and Technology at Peking University and the Shandong Provincial Education Association for International Exchanges.

References (29)

  • G.K.B. Costa et al.

    J. Alloys Compd.

    (2012)
  • G.K.B. Costa et al.

    Opt. Mater.

    (2009)
  • T. Suzuki et al.

    J. Luminescence

    (2010)
  • K. Wu et al.

    J. Cryst. Growth

    (2010)
  • E. Wendler et al.

    Nucl. Instrum. Methods Phys. Res. B

    (2016)
  • E. Wendler et al.

    Nucl. Instrum. Methods Phys. Res. B

    (2016)
  • X.Z. Liu et al.

    Opt. Commun.

    (2008)
  • L.L. Wang et al.

    Appl. Surf. Sci.

    (2010)
  • T.D. Shen et al.

    Appl. Phys. Lett.

    (2007)
  • E.A. Giess

    J. Appl. Phys.

    (1962)
  • B.A. Scott et al.

    Appl. Phys. Lett.

    (1972)
  • Z. Galazka et al.

    Phys. Status Solidi A

    (2015)
  • D.Nd. Faye et al.

    J. Phys. Chem. C

    (2016)
  • J. Kennedy et al.

    Nanotechnology

    (2011)

    • Cited by (5)

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