Optical and thermal performance of transparent ZnMgO/ZnO
quantum well heterostructures
M. R. Wagner
1
, J. S. Reparaz
1
, G. Callsen
1
, G. M. O. Pahn
1
, A. Franke
1
, C. Nenstiel
1
,
A. Hoffmann
1
, Maxime Hugues
2
, Monique Teysseire
2
, J. M. Chauveau
2,3
1
Technical University Berlin, institute of solid state physics, 10623 Berlin, Germany
2
CNRS-CRHEA, rue Bernard Grégory, 06560 Valbonne France
3
Physics Dept., University Nice Sophia Antipolis, 06102 Nice, France
corresponding author:
The progress in the performance of wurtzite quantum well heterostructures in the past decade
is strongly driven by the reduction or elimination of polarization fields at the heterointerfaces
due to the usage of nonpolar or semipolar growth directions. Among those, nonpolar ZnO
based quantum well (QW) heterostructures are promising examples for UV light emitters and
polariton lasers due to the combination of large exciton binding energies with the possibility
of large energy band gap engineering. In addition, the prospect of ZnO based quantum cas-
cade lasers (QCLs) was most recently suggested [1]. At the same time, the material system is
fully compatible to ZnO based TCOs which pave the way for complete homoepitaxial growth
and fabrication of oxide based optoelectronic devices. Apart from the largely resolved elec-
tric field induced limitations caused by the quantum confined Stark effect, thermal limitations
in high power emitters and devices become more and more crucial due to the large thermal
interface resistance in multi-interface heterostructures. In this regard, the prospect of room
temperature coherent phonon heat conduction in ZnMgO multi quantum well structures is
extremely exciting as was recently reported in GaAs/AlAs superlattices up to about 150~K
[2].
In this contribution, we present a detailed comparison of the optical and thermal properties of
ZnO based quantum well structures with varying Mg content (20 - 40 %) and QW thickness
(2 - 5 nm). High resolution cathodoluminescence maps reveal the spatial distribution of the
localized and free exciton emission in the quantum well region. The optical emission proper-
ties and carrier dynamics are analyzed by polarized, time resolved, power- and temperature
dependent luminescence measurements. Photoluminescence excitation (PLE) spectra are rec-
orded to identify the excitation channels and excited state splitting of the QW excitons which
are found to scale with increasing Mg content and QW thickness. In addition, the effective
thermal conductivity and phonons transport properties in these structures are investigated by
3-omega measurements. The results are discussed in terms of acoustic and thermal phonon
scattering at interfaces in multi-quantum well heterostructures. In addition, we show that
these kind of structures have promising properties regarding nanoscale thermal transport and
optoelectronic performance at the same time.
References:
[1] Zoterac, Zinc Oxide For Terahertz Cascade Devices, H2020-FETOPEN-2014-2015-RIA (2015)
[2] M. N. Luckyanova et al., Science 338, 936 (2012)
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