2
1 Introduction
chemistry. Naturally, its progress has a huge impact on other natural sciences and
modern technologies, such as information technologies, biology, or medicine, and
has implications for various industries. Obviously, the well explored domain of quantum structures with its utilisation of low-dimensional systems for quantum effects
(tailoring the eigen-states and therewith the resonances/energies ω(k) = E(k)/)
1
and potential landscapes of the order of the respective particles’ wavelengths (deBroglie wavelength λ = h/ p for matter waves)
2 for confinement, superpositions and
waveguiding has had a strong influence on photonic, electronic and optoelectronic
device engineering in the past decades.
Material engineering and physics have become the subject of intense research
towards the achievement of flexible, cheap and miniature optoelectronic devices,
both on the fundamental and the applied level. Within the overall research domain
concerning low-dimensional materials, which was previously dominated by conventional semiconductor heterostructure technology and by quantum dots (QDs), twodimensional materials (2DMs) have gained a large share, recently. Despite the popularity of novel and emerging materials, these well-established fields have matured
over the last decades as part of excessive integrated-circuit, light-source and photodetector development. Correspondingly, they have brought up various novel devices
ranging from single-photon sources (SPSs) over quantum-cascade lasers (QCLs) to
quantum-dot light-emitting diodes (QLEDs), while the utilisation of novel materials promises further improvements of such devices and even the discovery of more
exotic device concepts. All in all, the pool of attractive optoelectronic materials
has nowadays become extended from classical inorganic III/V semiconductors to
organic semiconductors, hybrid material systems, van-der-Waals (vdW) materials
and the perovskite material class.
Inherently, the systematic characterisation of functional nanomaterials and quantum structures remains an important constituent of many explorations concerning
novel or nanostructured material systems. Typically, the study of relevant platforms
is preceded or accompanied by theoretical predictions. Moreover, in the field of optoelectronics, optical spectroscopy has proven itself indispensable when it comes to
material characterisation, be it in the ultraviolet (UV), visible (VIS), infrared (IR) or
terahertz (THz) spectral region. Furthermore, in order to enable new and improved
device concepts, sensitivity and responsivity to photons of various energy are important aspects and probed with common optoelectronic techniques.
It is clear that different optoelectronic devices can benefit in the short or long
term from many of the discussed materials and nanostructured systems. These can,
on the one hand, range from particularly sensitive or broadband photodetectors to
wavelength-flexible coherent or broadband light sources. On the other hand, as part of
ongoing efforts to develop quantum technologies of the second generation, efficient
1 The availability of states of a system as a function of energy is expressed by the dimensionalitydependent density of states D(E), which reflects the excitation spectrum based on the energy–
phase-space relationship E(k) and plays a major role in the interactions and dynamics of particles
in that system.
2 Derived from the quantum-mechanical description of the classical particle momentum p = mv =
k = 2π/λ, with particle mass m, and momentum p, velocity v =
√
2E/m and wave-number k
in one-dimensional (vectorless) representation.
1 Introduction
chemistry. Naturally, its progress has a huge impact on other natural sciences and
modern technologies, such as information technologies, biology, or medicine, and
has implications for various industries. Obviously, the well explored domain of quantum structures with its utilisation of low-dimensional systems for quantum effects
(tailoring the eigen-states and therewith the resonances/energies ω(k) = E(k)/)
1
and potential landscapes of the order of the respective particles’ wavelengths (deBroglie wavelength λ = h/ p for matter waves)
2 for confinement, superpositions and
waveguiding has had a strong influence on photonic, electronic and optoelectronic
device engineering in the past decades.
Material engineering and physics have become the subject of intense research
towards the achievement of flexible, cheap and miniature optoelectronic devices,
both on the fundamental and the applied level. Within the overall research domain
concerning low-dimensional materials, which was previously dominated by conventional semiconductor heterostructure technology and by quantum dots (QDs), twodimensional materials (2DMs) have gained a large share, recently. Despite the popularity of novel and emerging materials, these well-established fields have matured
over the last decades as part of excessive integrated-circuit, light-source and photodetector development. Correspondingly, they have brought up various novel devices
ranging from single-photon sources (SPSs) over quantum-cascade lasers (QCLs) to
quantum-dot light-emitting diodes (QLEDs), while the utilisation of novel materials promises further improvements of such devices and even the discovery of more
exotic device concepts. All in all, the pool of attractive optoelectronic materials
has nowadays become extended from classical inorganic III/V semiconductors to
organic semiconductors, hybrid material systems, van-der-Waals (vdW) materials
and the perovskite material class.
Inherently, the systematic characterisation of functional nanomaterials and quantum structures remains an important constituent of many explorations concerning
novel or nanostructured material systems. Typically, the study of relevant platforms
is preceded or accompanied by theoretical predictions. Moreover, in the field of optoelectronics, optical spectroscopy has proven itself indispensable when it comes to
material characterisation, be it in the ultraviolet (UV), visible (VIS), infrared (IR) or
terahertz (THz) spectral region. Furthermore, in order to enable new and improved
device concepts, sensitivity and responsivity to photons of various energy are important aspects and probed with common optoelectronic techniques.
It is clear that different optoelectronic devices can benefit in the short or long
term from many of the discussed materials and nanostructured systems. These can,
on the one hand, range from particularly sensitive or broadband photodetectors to
wavelength-flexible coherent or broadband light sources. On the other hand, as part of
ongoing efforts to develop quantum technologies of the second generation, efficient
1 The availability of states of a system as a function of energy is expressed by the dimensionalitydependent density of states D(E), which reflects the excitation spectrum based on the energy–
phase-space relationship E(k) and plays a major role in the interactions and dynamics of particles
in that system.
2 Derived from the quantum-mechanical description of the classical particle momentum p = mv =
k = 2π/λ, with particle mass m, and momentum p, velocity v =
√
2E/m and wave-number k
in one-dimensional (vectorless) representation.