Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices

M. B. Ullah, M. Toporkov, V. Avrutin, Özgür, David Smith, H. Morkoç

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)

Abstract

We investigated the crystal structure, growth kinetics and electrical properties of BeMgZnO/ZnO heterostructures grown by Molecular Beam Epitaxy (MBE). Transmission Electron Microscopy (TEM) studies revealed that incorporation of Mg into the BeZnO solid solution eliminates the high angle grain boundaries that are the major structural defects in ternary BeZnO. The significant improvement of x-ray diffraction intensity from quaternary BeMgZnO alloy compared to ternary BeZnO was attributed to the reduction of lattice strain, which is present in the latter due to the large difference of covalent radii between Be and Zn (1.22 Å for Zn, 0.96 Å for Be). Incorporation of Mg, which has a larger covalent radius of 1.41Å, reduced the strain in BeMgZnO thin films and also enhanced Be incorporation on lattice sites in the wurtzite lattice. The Zn/(Be + Mg) ratio necessary to obtain single-crystal O-polar BeMgZnO on (0001) GaN/sapphire templates was found to increase with increasing substrate temperature:3.9, 6.2, and 8.3 at substrate temperatures of 450°C, 475°C, and 500°C, respectively. Based on analysis of photoluminescence spectra from Be0.03MgyZn0.97-yO and evolution of reflection high-energy electron diffraction patterns observed in situ during the MBE growth, it has been deduced that more negative formation enthalpy of MgO compared to ZnO and the increased surface mobility of Mg adatoms at elevated substrate temperatures give rise to the nucleation of a MgO-rich wurtzite phase at relatively low Zn/(Be + Mg) ratios. We have demonstrated both theoretically and experimentally that the incorporation of Be into the barrier in Zn-polar BeMgZnO/ZnO and O-polar ZnO/BeMgZnO polarization doped heterostructures allows the alignment of piezoelectric polarization vector with that of spontaneous polarization due to the change of strain sign, thus increasing the amount of net polarization. This made it possible to achieve Zn-polar BeMgZnO/ZnO heterostructures grown on GaN/sapphire templates with two-dimensional electron gas densities substantially exceeding those in Zn-polar MgZnO/ZnO and O-polar ZnO/MgZnO heterostructures with similar Mg content.

Original languageEnglish (US)
Title of host publicationOxide-Based Materials and Devices VIII 2017
PublisherSPIE
Volume10105
ISBN (Electronic)9781510606517
DOIs
StatePublished - 2017
EventOxide-Based Materials and Devices VIII 2017 - San Francisco, United States
Duration: Jan 29 2017Feb 1 2017

Other

OtherOxide-Based Materials and Devices VIII 2017
CountryUnited States
CitySan Francisco
Period1/29/172/1/17

Fingerprint

Epitaxy
Heterostructures
Molecular beam epitaxy
Heterojunctions
molecular beam epitaxy
Plasma
Polarization
Plasmas
Aluminum Oxide
polarization
Sapphire
wurtzite
sapphire
Substrates
templates
quaternary alloys
Substrate
Density of gases
Reflection high energy electron diffraction
Two dimensional electron gas

Keywords

  • 2DEG
  • BeMgZnO
  • Crystallinity
  • Growth kinetics
  • MBE
  • ZnO

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

Cite this

Ullah, M. B., Toporkov, M., Avrutin, V., Özgür, Smith, D., & Morkoç, H. (2017). Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices. In Oxide-Based Materials and Devices VIII 2017 (Vol. 10105). [101050J] SPIE. https://doi.org/10.1117/12.2260814

Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices. / Ullah, M. B.; Toporkov, M.; Avrutin, V.; Özgür, ; Smith, David; Morkoç, H.

Oxide-Based Materials and Devices VIII 2017. Vol. 10105 SPIE, 2017. 101050J.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Ullah, MB, Toporkov, M, Avrutin, V, Özgür, , Smith, D & Morkoç, H 2017, Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices. in Oxide-Based Materials and Devices VIII 2017. vol. 10105, 101050J, SPIE, Oxide-Based Materials and Devices VIII 2017, San Francisco, United States, 1/29/17. https://doi.org/10.1117/12.2260814
Ullah MB, Toporkov M, Avrutin V, Özgür , Smith D, Morkoç H. Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices. In Oxide-Based Materials and Devices VIII 2017. Vol. 10105. SPIE. 2017. 101050J https://doi.org/10.1117/12.2260814
Ullah, M. B. ; Toporkov, M. ; Avrutin, V. ; Özgür, ; Smith, David ; Morkoç, H. / Quaternary BeMgZnO by plasma-enhanced molecular beam epitaxy for BeMgZnO/ZnO heterostructure devices. Oxide-Based Materials and Devices VIII 2017. Vol. 10105 SPIE, 2017.
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abstract = "We investigated the crystal structure, growth kinetics and electrical properties of BeMgZnO/ZnO heterostructures grown by Molecular Beam Epitaxy (MBE). Transmission Electron Microscopy (TEM) studies revealed that incorporation of Mg into the BeZnO solid solution eliminates the high angle grain boundaries that are the major structural defects in ternary BeZnO. The significant improvement of x-ray diffraction intensity from quaternary BeMgZnO alloy compared to ternary BeZnO was attributed to the reduction of lattice strain, which is present in the latter due to the large difference of covalent radii between Be and Zn (1.22 {\AA} for Zn, 0.96 {\AA} for Be). Incorporation of Mg, which has a larger covalent radius of 1.41{\AA}, reduced the strain in BeMgZnO thin films and also enhanced Be incorporation on lattice sites in the wurtzite lattice. The Zn/(Be + Mg) ratio necessary to obtain single-crystal O-polar BeMgZnO on (0001) GaN/sapphire templates was found to increase with increasing substrate temperature:3.9, 6.2, and 8.3 at substrate temperatures of 450°C, 475°C, and 500°C, respectively. Based on analysis of photoluminescence spectra from Be0.03MgyZn0.97-yO and evolution of reflection high-energy electron diffraction patterns observed in situ during the MBE growth, it has been deduced that more negative formation enthalpy of MgO compared to ZnO and the increased surface mobility of Mg adatoms at elevated substrate temperatures give rise to the nucleation of a MgO-rich wurtzite phase at relatively low Zn/(Be + Mg) ratios. We have demonstrated both theoretically and experimentally that the incorporation of Be into the barrier in Zn-polar BeMgZnO/ZnO and O-polar ZnO/BeMgZnO polarization doped heterostructures allows the alignment of piezoelectric polarization vector with that of spontaneous polarization due to the change of strain sign, thus increasing the amount of net polarization. This made it possible to achieve Zn-polar BeMgZnO/ZnO heterostructures grown on GaN/sapphire templates with two-dimensional electron gas densities substantially exceeding those in Zn-polar MgZnO/ZnO and O-polar ZnO/MgZnO heterostructures with similar Mg content.",
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AU - Özgür,

AU - Smith, David

AU - Morkoç, H.

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N2 - We investigated the crystal structure, growth kinetics and electrical properties of BeMgZnO/ZnO heterostructures grown by Molecular Beam Epitaxy (MBE). Transmission Electron Microscopy (TEM) studies revealed that incorporation of Mg into the BeZnO solid solution eliminates the high angle grain boundaries that are the major structural defects in ternary BeZnO. The significant improvement of x-ray diffraction intensity from quaternary BeMgZnO alloy compared to ternary BeZnO was attributed to the reduction of lattice strain, which is present in the latter due to the large difference of covalent radii between Be and Zn (1.22 Å for Zn, 0.96 Å for Be). Incorporation of Mg, which has a larger covalent radius of 1.41Å, reduced the strain in BeMgZnO thin films and also enhanced Be incorporation on lattice sites in the wurtzite lattice. The Zn/(Be + Mg) ratio necessary to obtain single-crystal O-polar BeMgZnO on (0001) GaN/sapphire templates was found to increase with increasing substrate temperature:3.9, 6.2, and 8.3 at substrate temperatures of 450°C, 475°C, and 500°C, respectively. Based on analysis of photoluminescence spectra from Be0.03MgyZn0.97-yO and evolution of reflection high-energy electron diffraction patterns observed in situ during the MBE growth, it has been deduced that more negative formation enthalpy of MgO compared to ZnO and the increased surface mobility of Mg adatoms at elevated substrate temperatures give rise to the nucleation of a MgO-rich wurtzite phase at relatively low Zn/(Be + Mg) ratios. We have demonstrated both theoretically and experimentally that the incorporation of Be into the barrier in Zn-polar BeMgZnO/ZnO and O-polar ZnO/BeMgZnO polarization doped heterostructures allows the alignment of piezoelectric polarization vector with that of spontaneous polarization due to the change of strain sign, thus increasing the amount of net polarization. This made it possible to achieve Zn-polar BeMgZnO/ZnO heterostructures grown on GaN/sapphire templates with two-dimensional electron gas densities substantially exceeding those in Zn-polar MgZnO/ZnO and O-polar ZnO/MgZnO heterostructures with similar Mg content.

AB - We investigated the crystal structure, growth kinetics and electrical properties of BeMgZnO/ZnO heterostructures grown by Molecular Beam Epitaxy (MBE). Transmission Electron Microscopy (TEM) studies revealed that incorporation of Mg into the BeZnO solid solution eliminates the high angle grain boundaries that are the major structural defects in ternary BeZnO. The significant improvement of x-ray diffraction intensity from quaternary BeMgZnO alloy compared to ternary BeZnO was attributed to the reduction of lattice strain, which is present in the latter due to the large difference of covalent radii between Be and Zn (1.22 Å for Zn, 0.96 Å for Be). Incorporation of Mg, which has a larger covalent radius of 1.41Å, reduced the strain in BeMgZnO thin films and also enhanced Be incorporation on lattice sites in the wurtzite lattice. The Zn/(Be + Mg) ratio necessary to obtain single-crystal O-polar BeMgZnO on (0001) GaN/sapphire templates was found to increase with increasing substrate temperature:3.9, 6.2, and 8.3 at substrate temperatures of 450°C, 475°C, and 500°C, respectively. Based on analysis of photoluminescence spectra from Be0.03MgyZn0.97-yO and evolution of reflection high-energy electron diffraction patterns observed in situ during the MBE growth, it has been deduced that more negative formation enthalpy of MgO compared to ZnO and the increased surface mobility of Mg adatoms at elevated substrate temperatures give rise to the nucleation of a MgO-rich wurtzite phase at relatively low Zn/(Be + Mg) ratios. We have demonstrated both theoretically and experimentally that the incorporation of Be into the barrier in Zn-polar BeMgZnO/ZnO and O-polar ZnO/BeMgZnO polarization doped heterostructures allows the alignment of piezoelectric polarization vector with that of spontaneous polarization due to the change of strain sign, thus increasing the amount of net polarization. This made it possible to achieve Zn-polar BeMgZnO/ZnO heterostructures grown on GaN/sapphire templates with two-dimensional electron gas densities substantially exceeding those in Zn-polar MgZnO/ZnO and O-polar ZnO/MgZnO heterostructures with similar Mg content.

KW - 2DEG

KW - BeMgZnO

KW - Crystallinity

KW - Growth kinetics

KW - MBE

KW - ZnO

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