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X-ray beam probing of tensile strains in the process of waveguide formation in zinc oxide
Optik 160 (2018) 243–247
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
X-ray beam probing of tensile strains in the process of waveguide formation in zinc oxide X. Ming a,∗ , F. Lu b , C. Ma c , Y. Zhang a , R. Fan b a b c
School of Science, Tianjin Polytechnic University, Tianjin, 300387, China School of Information Science and Engineering, Shandong University, Jinan, 250100, China Department of Radiation Oncology, Qilu Hospital, Shandong University, Jinan, 250012, China
a r t i c l e
i n f o
Article history: Received 3 January 2018 Accepted 27 January 2018 Keywords: Zinc oxide Tensile strain Waveguide
a b s t r a c t Tensile strain and optical confinement in helium-implanted zinc oxide are investigated. High-resolution x-ray diffraction, prism coupling and end-face coupling technique are used to examine the implantation-induced structural changes and waveguide properties. The results show that tensile strain distribution is approximate follow the profile of lattice damage. Both contribute to the decrease of refractive index in zinc oxide. When an appropriate implantation depth is applied, laser beam can be confined between crystal surface and the reduced index layer. © 2018 Elsevier GmbH. All rights reserved.
1. Introduction Zinc oxide (ZnO) attracts great interest due to its wide range of promising applications in a variety of devices [1–4]. It is an alternative to gallium nitride, another wide-gap semiconductor which is used for production of various optoelectronic devices. Many of applications of ZnO involves in polycrystalline or amorphous materials. However, the widespread usage of single crystal ZnO would greatly benefit for future integrated optical systems owing to its high radiation hardness, mature crystal growth processes, and advanced material modification technology [5,6]. Introduction of exotic ions into a host material will cause distinct change in microstructure and macroscopic properties, altering the material potentialities [7–9]. Ion implantation can be used to introduce ions into ZnO with accurate control over depth and lateral concentration. The application of ion irradiation for material processing includes not only integrated electronic circuits and ion slicing for film fabrication but also refractive-index tuning for waveguide. Optical waveguide is a basic component for the miniaturization of electro-optical devices and a primary objective in the development of optical communications [10,11]. In ion-implanted waveguide, radiation induced effects, including lattice strain, damage profile and index modification, are the significant contributing factors for formation of waveguide, which are of fundamental interest in investigating ion-implanted ZnO. In this paper, strain distribution and waveguide properties are measured and analyzed by corresponding methods. This study can give insight into the mechanism of ion-crystal interaction and provide a reference for setting up optimum conditions for ZnO based devices.
∗ Corresponding author. E-mail address: [email protected] (X. Ming). https://doi.org/10.1016/j.ijleo.2018.01.099 0030-4026/© 2018 Elsevier GmbH. All rights reserved.
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Fig. 1. (a) Schematic plots of waveguide formation in zinc oxide. (b) The range of helium ions in the near-surface region.
2. Experiments Z-cut ZnO single crystals, with a size of 0.5 × 5 × 10 mm3 , are grown by the hydrothermal technique. Helium ions are implanted into the optically polished face of the samples, see Fig. 1. The energy of helium ions are 260 keV and 2 MeV, and the ion doses are 1 × 1016 and 2 × 1016 ions/cm2 , respectively. Ion implantation is performed in vacuum at room temperature by a 2 × 1.7 MV tandem accelerator at Peking University and an implanter at the Institute of Semiconductor, Chinese Academy of Sciences. After implantation, high resolution x-ray diffraction (HR-XRD) measurements are carried out in an AXS HRXRD D5005 system from Bruker Inc. with Cu-K␣1 radiation source. The classic m-line arrangement is used to investigate the properties of the waveguide. A prism coupling technique (via a prism coupler, Metricon 2010, USA) is used to measure the effective refractive indices of waveguide modes. The near-field image of waveguide is obtained via an end-face coupling setup. The laser intensity profile is imaged onto a CCD camera. 3. Results and discussion Ion implantation is a effective method to modify material properties. Stopping and ranges of ions in matter (SRIM) code is used to simulate the process of helium implantation [12,13]. Fig. 2(a) shows the energy loss and the ion concentration of the helium implanted into ZnO. As we can see, helium ions lose most of their energies by electronic ionizations along the path of helium trajectory, usually with occurrence of the formation of point defects. At the end of the ions track, nuclear collisions result in lattice disorder and change of the material density. It can be seen that the deposited helium ions are mainly located at the track end at a depth of 0.95 m. The relative atom displacement induced by implantation versus the penetration depth is presented in Fig. 2(b). For 260 keV sample, there is about 1% and 2% atom displacement at the ion track end for the implantation fluence at 1 × 1016 and 2 × 1016 ions/cm2 , respectively. When high energy 2.0 MeV ion is applied under the same ion fluence, atom displacement at the ion track end has the similar profile as that of 260 keV sample. Lattice modification in the implanted ZnO was analyzed by using HR-XRD [14,15]. Bragg’s Law is the theoretical basis of x-ray diffraction. According to the equation n = 2d sin, the change in the lattice constant d corresponds to the change in the position of a diffraction peak at , which can be obtained by differentiating Bragg’s equation d/d = −cot. In an implanted ZnO, the interplanar space of the lattice can be modified by introducing helium ions and defects. Dilating the crystal lattice shifts the peak toward < Bragg (left side of the main sharp diffraction peak) owing to local lattice expansion by ion interstitials. This behavior is a characteristic of extended interplanar space along the surface normal direction. Fig. 3 shows the experimental HR-XRD roking curves from the two implantation z-cut ZnO samples and one unimplanted bulk one. All curves show a main sharp diffraction Bragg peak located at 2 = 34.4, produced by diffraction of the unperturbed part of substrates. The main peak from unimplanted sample is much narrower than that of the helium implanted samples, showing that unimplanted ZnO has better single crystalline characteristics. The diffraction curves from implanted samples show some asymmetric broadened satellite peaks near Bragg peak. These oscillating fringes at 2 < 34.4 are arised from diffraction of the damaged layer. The number of the satellite peaks is a measure of the strain in the implanted zone, and it
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Fig. 2. (a) Energy loss and ion concentration versus the penetration depth of ions; (b) Relative atom displacement induced by ion implantation versus the penetration depth of ions.
Fig. 3. Experimental XRD curves close to the (002) Bragg reflection (a) implanted with doses of 2 × 1016 ions/cm2 (b) with doses of 1 × 1016 ions/cm2 (c) unimplanted bulk material.
increases with increasing implantation dose. These shifted peaks toward the low angle side of the main Bragg peak, which means that tensile strain is induced in the implanted samples, that is, the interplanar space of ZnO expand along the z orientation. To study the relationship between the lattice dilatation and HR-XRD results, simulation of the XRD curves of the as implanted samples was carried out with the web-based computer code GID sl [16]. The simulation assumes that the normal strain d/d proportional to the defect. The damaged region is divided into some sublayers with given thickness, and each
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Fig. 4. (a) Simulated X-ray diffraction curves close to the (002) Bragg reflection in ZnO implanted with fluences of 2 × 1016 ions/cm2 . (b) Strain profile compared to both the relative atom displacement and the helium concentration profiles.
Fig. 5. (a) Relative intensity of TM polarized light reflected from the prism versus the effective refractive index of the incident light in the ZnO waveguide formed by helium implantation; (b) Calculated refractive index distribution of the waveguide. Inset: Near-field profile of the waveguide collected by CCD camera.
has an adjustable d/d value. As a starting point for the calculation, the strain d/d is assumed to follow helium concentration distribution given by the SRIM code. Simulated XRD curves were then gradually modified by adjusting the d/d distribution to fit the experimental curves. Fig. 4(a) shows the simulated X-ray curves for the sample implanted with dose of 2 × 1016 ions/cm2 . The experimental curve and simulated results agree well when taking the strain distributions plotted in Fig. 4(b). Although noisy simulated results are obtained because of discrete rather than continuous d/d data used in the calculation, the curve trend of calculation results conform to the experimental results very well. The strain profile exhibits a near Gaussian distribution, but is much narrower than that of atom displacement profile. It can be found that under the same ion fluence the maximum d/d ∼ 0.006 in implanted ZnO is much smaller than that of some materials, such as SiC.15 Ion concentration, calculated by SRIM code, is also given for comparison. If the implanted helium ions are assumed to be homogeneously distributed in the x and y directions parallel to the material surface and confined within a narrow z distribution, the helium interstitials will dilate the ZnO lattice along the z direction. The results show that the internal strain is mainly induced and concentrated at the region of heavily damaged lattice layer. Due to the high radiation damage resistance of ZnO, obvious strain can be produced only when ion concentration is higher than ∼1016 ions/cm2 . Fig. 5(a) shows the measured relative intensity spectra of transverse magnetic (TM) polarized light reflected from the prism versus the effective refractive index of the incident light in the ZnO waveguide formed by 2.0 MeV He ion implanta-
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tion. The corresponding refractive index of the substrate nsub (extraordinary refractive index ne = 2.0046 at the wavelength 633 nm) is marked as well. Two modes have been excited in this waveguide. The near field mode profile is collected by the end-face coupling method at wavelength of 633 nm, which is shown in inset of Fig. 5(b). Light can be confined in the waveguide. According to the m-line spectrum, we reconstruct the profile of the refractive index in this waveguide by applying the reflectivity calculation method [17] which has been proved particularly suitable for describing refractive index profiles in ion implanted waveguide. Fig. 5(b) shows the graphical representation of refractive index profile of waveguide by 2 MeV helium implantation at dose of 2 × 1016 ions/cm2 . Refractive index of the substrate (nsub ) is also marked. As is indicated, only 0.1% refractive-index decrease occurs at the end of the ion range, which serves as one of the waveguide barrier to confine the light propagation. By comparing the index profile with the distributions of atom displacement, d/d and ion concentration, it can be found that the refractive index variation approximate follows the strain distribution. The index decrease in optical barrier may be the result of lattice damage and strain. 4. Conclusions In conclusion, we have demonstrated the tensile strains in the process of ZnO waveguide formation by energetic helium ions implantation. Based on experimental and simulated results, tensile strain profiles and waveguide properties study are presented. The tensile strain distribution contributes to the decrease of refractive index in zinc oxide which can confine the light efficiently. Acknowledgments This work was supported by Tianjin Research Program of Application Foundation and Advanced Technology (Grant No. 14JCQNJC01300) and National Natural Science Foundation of China (Grant Nos. 11475105, 11304224). References [1] W. Liu, S.L. Gu, J.D. Ye, S.M. Zhu, S.M. Liu, X. Zhou, C.L. Zhang, Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique, Appl. Phys. Lett. 88 (2006) 092101. [2] K.W. Kim, N.J. Choi, K.B. Kim, M. Kim, S.N. Lee, Growth and characterization of nonpolar (10-10) ZnO transparent conductive oxide on semipolar (11e22) GaN-based light-emitting diodes, J. Alloys Compd. 666 (2016) 88–92. [3] Z. Wang, J. Song, Piezoelectric nanogenerators based on zinc oxide nanowire arrays, Science 312 (2006) 242–246. [4] Ü. Özgür, Ya.I. Alivov, C. Liu, A. Teke, M.A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, H. Morkoc¸, A comprehensive review of ZnO materials and devices, J. Appl. Phys. 98 (2005) 041301. [5] X. Zhao, L. Chen, Y. He, Nanosecond X-ray detector based on high resistivity ZnO single crystal semiconductor, Appl. Phys. Lett. 108 (2016) 171103. [6] E.B. Magnusson, B.H. Williams, R. Manenti, Surface acoustic wave devices on bulk ZnO crystals at low temperature, Appl. Phys. Lett. 106 (2015) 063509. [7] R. Ratajczak, S. Prucnal, E. Guziewicz, C. Mieszczynski, D. Snigurenko, M. Stachowicz, W. Skorupa, A. Turos, The photoluminescence response to structural changes of Yb implanted ZnO crystals subjected to non-equilibrium processing, J. Appl. Phys. 121 (2017) 075101. [8] C. Bhoodoo, A. Hupfer, L. Vines, E.V. Monakhov, B.G. Svensson, Evolution kinetics of elementary point defects in ZnO implanted with low fluences of helium at cryogenic temperature, Phys. Rev. B 94 (2016) 205204. [9] F. Yaqoob, M. Huang, Effects of high-dose hydrogen implantation on defect formation and dopant diffusion in silver implanted ZnO crystals, J. Appl. Phys. 120 (2016) 045101. [10] S. Lee, T. Goto, H. Miyazaki, T. Yao, Waveguide lasing from V-shaped ZnO microstructure, Opt. Lett. 38 (2013) 2413–2415. [11] Q. Zhang, J. Qi, J. Zhao, X. Li, Y. Zhang, Multi-zone light emission in a one-dimensional ZnO waveguide with hybrid structures, Opt. Mater. Express 1 (2011) 173–178. [12] J.F. Ziegler, SRIM-2003, Nucl. Instrum. Methods Phys. Res. B 219–220 (2004) 1027–1036. [13] J.F. Ziegler, computer code, SRIM, http://www.srim.org. [14] C. Ma, F. Lu, B. Xu, R. Fan, Lattice modification in KTiOPO4 by hydrogen and helium sequentially implantation in submicrometer depth, Appl. Phys. Lett. 108 (2016) 193110. [15] S. Leclerc, A. Declémy, M.F. Beaufort, C. Tromas, J.F. Barbot, Swelling of SiC under helium implantation, J. Appl. Phys. 98 (2005) 113506. [16] S. Stepanov, computer code, GID-sl, http://sergey.gmca.aps.anl.gov/gidsl.html. [17] P.J. Chandler, F.L. Lama, A new approach to the determination of planar waveguide profiles by means of a non-stationary mode index calculation, Opt. Acta 33 (1986) 127–143.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
X-ray beam probing of tensile strains in the process of waveguide formation in zinc oxide X. Ming a,∗ , F. Lu b , C. Ma c , Y. Zhang a , R. Fan b a b c
School of Science, Tianjin Polytechnic University, Tianjin, 300387, China School of Information Science and Engineering, Shandong University, Jinan, 250100, China Department of Radiation Oncology, Qilu Hospital, Shandong University, Jinan, 250012, China
a r t i c l e
i n f o
Article history: Received 3 January 2018 Accepted 27 January 2018 Keywords: Zinc oxide Tensile strain Waveguide
a b s t r a c t Tensile strain and optical confinement in helium-implanted zinc oxide are investigated. High-resolution x-ray diffraction, prism coupling and end-face coupling technique are used to examine the implantation-induced structural changes and waveguide properties. The results show that tensile strain distribution is approximate follow the profile of lattice damage. Both contribute to the decrease of refractive index in zinc oxide. When an appropriate implantation depth is applied, laser beam can be confined between crystal surface and the reduced index layer. © 2018 Elsevier GmbH. All rights reserved.
1. Introduction Zinc oxide (ZnO) attracts great interest due to its wide range of promising applications in a variety of devices [1–4]. It is an alternative to gallium nitride, another wide-gap semiconductor which is used for production of various optoelectronic devices. Many of applications of ZnO involves in polycrystalline or amorphous materials. However, the widespread usage of single crystal ZnO would greatly benefit for future integrated optical systems owing to its high radiation hardness, mature crystal growth processes, and advanced material modification technology [5,6]. Introduction of exotic ions into a host material will cause distinct change in microstructure and macroscopic properties, altering the material potentialities [7–9]. Ion implantation can be used to introduce ions into ZnO with accurate control over depth and lateral concentration. The application of ion irradiation for material processing includes not only integrated electronic circuits and ion slicing for film fabrication but also refractive-index tuning for waveguide. Optical waveguide is a basic component for the miniaturization of electro-optical devices and a primary objective in the development of optical communications [10,11]. In ion-implanted waveguide, radiation induced effects, including lattice strain, damage profile and index modification, are the significant contributing factors for formation of waveguide, which are of fundamental interest in investigating ion-implanted ZnO. In this paper, strain distribution and waveguide properties are measured and analyzed by corresponding methods. This study can give insight into the mechanism of ion-crystal interaction and provide a reference for setting up optimum conditions for ZnO based devices.
∗ Corresponding author. E-mail address: [email protected] (X. Ming). https://doi.org/10.1016/j.ijleo.2018.01.099 0030-4026/© 2018 Elsevier GmbH. All rights reserved.
244
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Fig. 1. (a) Schematic plots of waveguide formation in zinc oxide. (b) The range of helium ions in the near-surface region.
2. Experiments Z-cut ZnO single crystals, with a size of 0.5 × 5 × 10 mm3 , are grown by the hydrothermal technique. Helium ions are implanted into the optically polished face of the samples, see Fig. 1. The energy of helium ions are 260 keV and 2 MeV, and the ion doses are 1 × 1016 and 2 × 1016 ions/cm2 , respectively. Ion implantation is performed in vacuum at room temperature by a 2 × 1.7 MV tandem accelerator at Peking University and an implanter at the Institute of Semiconductor, Chinese Academy of Sciences. After implantation, high resolution x-ray diffraction (HR-XRD) measurements are carried out in an AXS HRXRD D5005 system from Bruker Inc. with Cu-K␣1 radiation source. The classic m-line arrangement is used to investigate the properties of the waveguide. A prism coupling technique (via a prism coupler, Metricon 2010, USA) is used to measure the effective refractive indices of waveguide modes. The near-field image of waveguide is obtained via an end-face coupling setup. The laser intensity profile is imaged onto a CCD camera. 3. Results and discussion Ion implantation is a effective method to modify material properties. Stopping and ranges of ions in matter (SRIM) code is used to simulate the process of helium implantation [12,13]. Fig. 2(a) shows the energy loss and the ion concentration of the helium implanted into ZnO. As we can see, helium ions lose most of their energies by electronic ionizations along the path of helium trajectory, usually with occurrence of the formation of point defects. At the end of the ions track, nuclear collisions result in lattice disorder and change of the material density. It can be seen that the deposited helium ions are mainly located at the track end at a depth of 0.95 m. The relative atom displacement induced by implantation versus the penetration depth is presented in Fig. 2(b). For 260 keV sample, there is about 1% and 2% atom displacement at the ion track end for the implantation fluence at 1 × 1016 and 2 × 1016 ions/cm2 , respectively. When high energy 2.0 MeV ion is applied under the same ion fluence, atom displacement at the ion track end has the similar profile as that of 260 keV sample. Lattice modification in the implanted ZnO was analyzed by using HR-XRD [14,15]. Bragg’s Law is the theoretical basis of x-ray diffraction. According to the equation n = 2d sin, the change in the lattice constant d corresponds to the change in the position of a diffraction peak at , which can be obtained by differentiating Bragg’s equation d/d = −cot. In an implanted ZnO, the interplanar space of the lattice can be modified by introducing helium ions and defects. Dilating the crystal lattice shifts the peak toward < Bragg (left side of the main sharp diffraction peak) owing to local lattice expansion by ion interstitials. This behavior is a characteristic of extended interplanar space along the surface normal direction. Fig. 3 shows the experimental HR-XRD roking curves from the two implantation z-cut ZnO samples and one unimplanted bulk one. All curves show a main sharp diffraction Bragg peak located at 2 = 34.4, produced by diffraction of the unperturbed part of substrates. The main peak from unimplanted sample is much narrower than that of the helium implanted samples, showing that unimplanted ZnO has better single crystalline characteristics. The diffraction curves from implanted samples show some asymmetric broadened satellite peaks near Bragg peak. These oscillating fringes at 2 < 34.4 are arised from diffraction of the damaged layer. The number of the satellite peaks is a measure of the strain in the implanted zone, and it
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245
Fig. 2. (a) Energy loss and ion concentration versus the penetration depth of ions; (b) Relative atom displacement induced by ion implantation versus the penetration depth of ions.
Fig. 3. Experimental XRD curves close to the (002) Bragg reflection (a) implanted with doses of 2 × 1016 ions/cm2 (b) with doses of 1 × 1016 ions/cm2 (c) unimplanted bulk material.
increases with increasing implantation dose. These shifted peaks toward the low angle side of the main Bragg peak, which means that tensile strain is induced in the implanted samples, that is, the interplanar space of ZnO expand along the z orientation. To study the relationship between the lattice dilatation and HR-XRD results, simulation of the XRD curves of the as implanted samples was carried out with the web-based computer code GID sl [16]. The simulation assumes that the normal strain d/d proportional to the defect. The damaged region is divided into some sublayers with given thickness, and each
246
X. Ming et al. / Optik 160 (2018) 243–247
Fig. 4. (a) Simulated X-ray diffraction curves close to the (002) Bragg reflection in ZnO implanted with fluences of 2 × 1016 ions/cm2 . (b) Strain profile compared to both the relative atom displacement and the helium concentration profiles.
Fig. 5. (a) Relative intensity of TM polarized light reflected from the prism versus the effective refractive index of the incident light in the ZnO waveguide formed by helium implantation; (b) Calculated refractive index distribution of the waveguide. Inset: Near-field profile of the waveguide collected by CCD camera.
has an adjustable d/d value. As a starting point for the calculation, the strain d/d is assumed to follow helium concentration distribution given by the SRIM code. Simulated XRD curves were then gradually modified by adjusting the d/d distribution to fit the experimental curves. Fig. 4(a) shows the simulated X-ray curves for the sample implanted with dose of 2 × 1016 ions/cm2 . The experimental curve and simulated results agree well when taking the strain distributions plotted in Fig. 4(b). Although noisy simulated results are obtained because of discrete rather than continuous d/d data used in the calculation, the curve trend of calculation results conform to the experimental results very well. The strain profile exhibits a near Gaussian distribution, but is much narrower than that of atom displacement profile. It can be found that under the same ion fluence the maximum d/d ∼ 0.006 in implanted ZnO is much smaller than that of some materials, such as SiC.15 Ion concentration, calculated by SRIM code, is also given for comparison. If the implanted helium ions are assumed to be homogeneously distributed in the x and y directions parallel to the material surface and confined within a narrow z distribution, the helium interstitials will dilate the ZnO lattice along the z direction. The results show that the internal strain is mainly induced and concentrated at the region of heavily damaged lattice layer. Due to the high radiation damage resistance of ZnO, obvious strain can be produced only when ion concentration is higher than ∼1016 ions/cm2 . Fig. 5(a) shows the measured relative intensity spectra of transverse magnetic (TM) polarized light reflected from the prism versus the effective refractive index of the incident light in the ZnO waveguide formed by 2.0 MeV He ion implanta-
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tion. The corresponding refractive index of the substrate nsub (extraordinary refractive index ne = 2.0046 at the wavelength 633 nm) is marked as well. Two modes have been excited in this waveguide. The near field mode profile is collected by the end-face coupling method at wavelength of 633 nm, which is shown in inset of Fig. 5(b). Light can be confined in the waveguide. According to the m-line spectrum, we reconstruct the profile of the refractive index in this waveguide by applying the reflectivity calculation method [17] which has been proved particularly suitable for describing refractive index profiles in ion implanted waveguide. Fig. 5(b) shows the graphical representation of refractive index profile of waveguide by 2 MeV helium implantation at dose of 2 × 1016 ions/cm2 . Refractive index of the substrate (nsub ) is also marked. As is indicated, only 0.1% refractive-index decrease occurs at the end of the ion range, which serves as one of the waveguide barrier to confine the light propagation. By comparing the index profile with the distributions of atom displacement, d/d and ion concentration, it can be found that the refractive index variation approximate follows the strain distribution. The index decrease in optical barrier may be the result of lattice damage and strain. 4. Conclusions In conclusion, we have demonstrated the tensile strains in the process of ZnO waveguide formation by energetic helium ions implantation. Based on experimental and simulated results, tensile strain profiles and waveguide properties study are presented. The tensile strain distribution contributes to the decrease of refractive index in zinc oxide which can confine the light efficiently. Acknowledgments This work was supported by Tianjin Research Program of Application Foundation and Advanced Technology (Grant No. 14JCQNJC01300) and National Natural Science Foundation of China (Grant Nos. 11475105, 11304224). References [1] W. Liu, S.L. Gu, J.D. Ye, S.M. Zhu, S.M. Liu, X. Zhou, C.L. Zhang, Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique, Appl. Phys. Lett. 88 (2006) 092101. [2] K.W. Kim, N.J. Choi, K.B. Kim, M. Kim, S.N. Lee, Growth and characterization of nonpolar (10-10) ZnO transparent conductive oxide on semipolar (11e22) GaN-based light-emitting diodes, J. Alloys Compd. 666 (2016) 88–92. [3] Z. Wang, J. Song, Piezoelectric nanogenerators based on zinc oxide nanowire arrays, Science 312 (2006) 242–246. [4] Ü. Özgür, Ya.I. Alivov, C. Liu, A. Teke, M.A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, H. Morkoc¸, A comprehensive review of ZnO materials and devices, J. Appl. Phys. 98 (2005) 041301. [5] X. Zhao, L. Chen, Y. He, Nanosecond X-ray detector based on high resistivity ZnO single crystal semiconductor, Appl. Phys. Lett. 108 (2016) 171103. [6] E.B. Magnusson, B.H. Williams, R. Manenti, Surface acoustic wave devices on bulk ZnO crystals at low temperature, Appl. Phys. Lett. 106 (2015) 063509. [7] R. Ratajczak, S. Prucnal, E. Guziewicz, C. Mieszczynski, D. Snigurenko, M. Stachowicz, W. Skorupa, A. Turos, The photoluminescence response to structural changes of Yb implanted ZnO crystals subjected to non-equilibrium processing, J. Appl. Phys. 121 (2017) 075101. [8] C. Bhoodoo, A. Hupfer, L. Vines, E.V. Monakhov, B.G. Svensson, Evolution kinetics of elementary point defects in ZnO implanted with low fluences of helium at cryogenic temperature, Phys. Rev. B 94 (2016) 205204. [9] F. Yaqoob, M. Huang, Effects of high-dose hydrogen implantation on defect formation and dopant diffusion in silver implanted ZnO crystals, J. Appl. Phys. 120 (2016) 045101. [10] S. Lee, T. Goto, H. Miyazaki, T. Yao, Waveguide lasing from V-shaped ZnO microstructure, Opt. Lett. 38 (2013) 2413–2415. [11] Q. Zhang, J. Qi, J. Zhao, X. Li, Y. Zhang, Multi-zone light emission in a one-dimensional ZnO waveguide with hybrid structures, Opt. Mater. Express 1 (2011) 173–178. [12] J.F. Ziegler, SRIM-2003, Nucl. Instrum. Methods Phys. Res. B 219–220 (2004) 1027–1036. [13] J.F. Ziegler, computer code, SRIM, http://www.srim.org. [14] C. Ma, F. Lu, B. Xu, R. Fan, Lattice modification in KTiOPO4 by hydrogen and helium sequentially implantation in submicrometer depth, Appl. Phys. Lett. 108 (2016) 193110. [15] S. Leclerc, A. Declémy, M.F. Beaufort, C. Tromas, J.F. Barbot, Swelling of SiC under helium implantation, J. Appl. Phys. 98 (2005) 113506. [16] S. Stepanov, computer code, GID-sl, http://sergey.gmca.aps.anl.gov/gidsl.html. [17] P.J. Chandler, F.L. Lama, A new approach to the determination of planar waveguide profiles by means of a non-stationary mode index calculation, Opt. Acta 33 (1986) 127–143.