8.1 Summary
231
semiconducting post-TMDC material gallium telluride utilised for sensing applications. The broad variety of material properties and applications is currently the main
driving force for extensive research worldwide in this domain.
In this work, the endeavours to characterise novel nanomaterial systems as well
as quantum structures with the help of optical techniques and the achievements are
highlighted within the context of international and domestic ongoing research efforts.
In recent years, the influences of the substrate material, dielectric environment
and stacking configuration or order have been discussed for these fascinating monolayer semiconductors by various works. A number of them conducted by the author
and co-workers in optical studies at cryogenic temperatures and room temperature
have addressed energetics, dynamics and vibronics of the monolayers investigated
with spectroscopic methods. Based on excellent samples from partner groups at the
Columbia University and the Stevens Institute of Technology from the U.S., various interesting effects were reported and important material comparisons enabled.
Among others, the impact of the substrate choice on biexciton observation in WSe 2 ,
the difference in polarisation anisotropy for AA’ and AB stacked WS 2 bilayers, and
the occurrence of meV energy–momentum dispersion for excitons within the light
cone—understood as exciton–polaritons—for high-quality monolayer samples have
been demonstrated. In addition, heterostructuring capabilities with regard to a modification of electronic properties and charge-transfer states were explored, making
primarily use of homemade van-der-Waals stacks.
For efficient and sensitive photodetection or sensing, new concepts employing
2D materials, such as graphene and related materials, are being intensively investigated in the whole research community. One approach to combine colloidal quantum dots and a graphene-based field-effect transistor led to a hybrid photodetector
with gate-tunable Förster energy transfer between dots and graphene channel, as
demonstrated in a joint study of the collaborating physicists from Marburg, Germany,
and Hangzhou, China. In another study, it was demonstrated that gold-nanoparticledecorated GaTe can act as a very sensitive probe for certain aromatic molecules and
could become a promising candidate for surface-enhanced Raman spectroscopy.
Also, other materials such as the material class of the perovskites have shown
very interesting properties that render them attractive candidates for optoelectronic
devices, such as solar cells or lasers. Typically, lead–halide perovskites provide a
fruitful testbed for optical studies, which were performed collaboratively by the
author with domestic and international partners. In a first step, a very promising
material of this class was analysed on a wide relevant temperature range to probe
optoelectronic properties, enabled by the efforts of the partner group in Hangzhou.
Following that, further characterisation of the charge-carrier dynamics and photoluminescence properties was achieved. Recently, nonlinear optics in single-crystalline
perovskites provided by a group from Tübingen, Germany, were probed with a Zscan technique, which had been previously employed by the author for the systematic
investigations on nonlinear lensing (and in the same breath on nonlinear absorption)
in semiconductor disk laser chips that are also highlighted in this work.
In addition to the conventional optoelectronic microdevices, future on-chip optoelectronic circuitry for computing or possibly biomedical applications will highly
231
semiconducting post-TMDC material gallium telluride utilised for sensing applications. The broad variety of material properties and applications is currently the main
driving force for extensive research worldwide in this domain.
In this work, the endeavours to characterise novel nanomaterial systems as well
as quantum structures with the help of optical techniques and the achievements are
highlighted within the context of international and domestic ongoing research efforts.
In recent years, the influences of the substrate material, dielectric environment
and stacking configuration or order have been discussed for these fascinating monolayer semiconductors by various works. A number of them conducted by the author
and co-workers in optical studies at cryogenic temperatures and room temperature
have addressed energetics, dynamics and vibronics of the monolayers investigated
with spectroscopic methods. Based on excellent samples from partner groups at the
Columbia University and the Stevens Institute of Technology from the U.S., various interesting effects were reported and important material comparisons enabled.
Among others, the impact of the substrate choice on biexciton observation in WSe 2 ,
the difference in polarisation anisotropy for AA’ and AB stacked WS 2 bilayers, and
the occurrence of meV energy–momentum dispersion for excitons within the light
cone—understood as exciton–polaritons—for high-quality monolayer samples have
been demonstrated. In addition, heterostructuring capabilities with regard to a modification of electronic properties and charge-transfer states were explored, making
primarily use of homemade van-der-Waals stacks.
For efficient and sensitive photodetection or sensing, new concepts employing
2D materials, such as graphene and related materials, are being intensively investigated in the whole research community. One approach to combine colloidal quantum dots and a graphene-based field-effect transistor led to a hybrid photodetector
with gate-tunable Förster energy transfer between dots and graphene channel, as
demonstrated in a joint study of the collaborating physicists from Marburg, Germany,
and Hangzhou, China. In another study, it was demonstrated that gold-nanoparticledecorated GaTe can act as a very sensitive probe for certain aromatic molecules and
could become a promising candidate for surface-enhanced Raman spectroscopy.
Also, other materials such as the material class of the perovskites have shown
very interesting properties that render them attractive candidates for optoelectronic
devices, such as solar cells or lasers. Typically, lead–halide perovskites provide a
fruitful testbed for optical studies, which were performed collaboratively by the
author with domestic and international partners. In a first step, a very promising
material of this class was analysed on a wide relevant temperature range to probe
optoelectronic properties, enabled by the efforts of the partner group in Hangzhou.
Following that, further characterisation of the charge-carrier dynamics and photoluminescence properties was achieved. Recently, nonlinear optics in single-crystalline
perovskites provided by a group from Tübingen, Germany, were probed with a Zscan technique, which had been previously employed by the author for the systematic
investigations on nonlinear lensing (and in the same breath on nonlinear absorption)
in semiconductor disk laser chips that are also highlighted in this work.
In addition to the conventional optoelectronic microdevices, future on-chip optoelectronic circuitry for computing or possibly biomedical applications will highly