Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO

K. I. Gries, T. A. Wassner, S. Vogel, J. Bruckbauer, I. Häusler, R. Straubinger, A. Beyer, A. Chernikov, B. Laumer, M. Kracht, C. Heiliger, J. Janek, S. Chatterjee, K. Volz, M. Eickhoff

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.
LanguageEnglish
Article number045706
Number of pages8
JournalJournal of Applied Physics
Volume118
Issue number4
DOIs
Publication statusPublished - 24 Jul 2015

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halites
wurtzite
self assembly
annealing
sapphire
screws
red shift
epitaxy
spinel
temperature
optical spectrum
magnesium
seeds
optical absorption
molecular beam epitaxy
templates
absorption spectra
photoluminescence
transmission electron microscopy

Keywords

  • photoluminescence
  • transmission electron microscopy
  • phase separation

Cite this

Gries, K. I. ; Wassner, T. A. ; Vogel, S. ; Bruckbauer, J. ; Häusler, I. ; Straubinger, R. ; Beyer, A. ; Chernikov, A. ; Laumer, B. ; Kracht, M. ; Heiliger, C. ; Janek, J. ; Chatterjee, S. ; Volz, K. ; Eickhoff, M. / Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO. In: Journal of Applied Physics. 2015 ; Vol. 118, No. 4.
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abstract = "The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.",
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Gries, KI, Wassner, TA, Vogel, S, Bruckbauer, J, Häusler, I, Straubinger, R, Beyer, A, Chernikov, A, Laumer, B, Kracht, M, Heiliger, C, Janek, J, Chatterjee, S, Volz, K & Eickhoff, M 2015, 'Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO' Journal of Applied Physics, vol. 118, no. 4, 045706. https://doi.org/10.1063/1.4926776

Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO. / Gries, K. I.; Wassner, T. A.; Vogel, S.; Bruckbauer, J.; Häusler, I.; Straubinger, R.; Beyer, A.; Chernikov, A.; Laumer, B.; Kracht, M.; Heiliger, C.; Janek, J.; Chatterjee, S.; Volz, K.; Eickhoff, M.

In: Journal of Applied Physics, Vol. 118, No. 4, 045706, 24.07.2015.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO

AU - Gries, K. I.

AU - Wassner, T. A.

AU - Vogel, S.

AU - Bruckbauer, J.

AU - Häusler, I.

AU - Straubinger, R.

AU - Beyer, A.

AU - Chernikov, A.

AU - Laumer, B.

AU - Kracht, M.

AU - Heiliger, C.

AU - Janek, J.

AU - Chatterjee, S.

AU - Volz, K.

AU - Eickhoff, M.

PY - 2015/7/24

Y1 - 2015/7/24

N2 - The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.

AB - The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.

KW - photoluminescence

KW - transmission electron microscopy

KW - phase separation

UR - http://scitation.aip.org/content/aip/journal/jap/118/4/10.1063/1.4926776

U2 - 10.1063/1.4926776

DO - 10.1063/1.4926776

M3 - Article

VL - 118

JO - Journal of Applied Physics

T2 - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 4

M1 - 045706

ER -