Scientific Highlights

PDI researchers have achieved the first epitaxial growth of scandium nitride in the unusual (113) orientation, expanding the possibilities for nitride materials research. Published in ACS Applied Electronic Materials, this breakthrough opens new pathways for designing nitride-based materials with tailored properties for future electronic and optoelectronic applications.

A new study overturns a key assumption in solar cell design: that triplet excitons are always bad news. Researchers have discovered that, under the right conditions, these excited states don’t necessarily lead to large voltage losses—offering fresh insight into how organic solar cells can be made even more efficient.

A new study from the Nanoanalytics CReA, featured in Semiconductor Today, presents a surface-smoothing technique in MBE that boosts carrier mobility in InAs quantum wells on GaAs, especially below 120 K. [Featured in Semiconductor Today]

The quantum Hall effect (QHE) is one of the most remarkable phenomena in condensed matter physics. Textbooks still describe it in terms of perfect one-dimensional edge channels that carry a dissipationless current around an insulating bulk. More recently, this picture has been challenged for neglecting Coulomb interactions between current-carrying electrons. In our experiment from the Nanoelectronics CReA, we used an additional contact at the center of the Hall bar to detect the predicted bulk current — to our knowledge, the first direct measurement of its kind.

A new study by researchers at the Paul-Drude-Institut für Festkörperelektronik (PDI), published in Journal of Physics D: Applied Physics, demonstrates a major advancement in the growth of high-quality indium gallium nitride (InₓGa₁₋ₓN) layers using plasma-assisted molecular beam epitaxy (MBE).

Researchers at the Paul Drude Institute for Solid State Electronics, in collaboration with institutions in Berlin, London, Oxford, and Hamburg, report the formation of a two-dimensional electron gas (2DEG) with room-temperature electron mobility values up to 119 cm²/Vs at the interface between epitaxial layers of BaSnO₃ (BSO) and LaInO₃ (LIO). This mobility represents the highest value reported to date for a 2DEG in perovskite oxide systems at room temperature.

After more than half a century of research, understanding electron scattering mechanisms in scandium nitride (ScN) has remained a significant challenge, primarily due to high impurity concentrations in scandium sources. In a groundbreaking study published in Phys. Rev. Appl. 22, 014067 (2024), researchers at PDI overcame this long-standing limitation by growing high-purity ScN(111) layers on nearly lattice-matched semi-insulating GaN(0001) using plasma-assisted molecular beam epitaxy.

An invited paper authored by PDI scientists in collaboration with DLR, INP, and Lytid SAS, has recently been selected as a Featured Paper in the Special Issue of IEEE Transactions on Terahertz Science and Technology “Selected Emerging Trends in Terahertz Science and Technology”. The paper details advancements in designing and fabricating terahertz quantum-cascade lasers and explores their applications in high-resolution spectroscopy, demonstrating their potential for atmospheric studies and industrial diagnostics.

Color centers in solids, particularly optically addressable spin centers, are promising for quantum technologies due to their ability to interact with light. Silicon carbide (SiC) is gaining attention for its compatibility with CMOS technology and its coherent spin centers, such as the negatively charged silicon vacancy (VSi) with spin S=3/2. A recent study by researchers from the Paul-Drude-Institut, Helmholtz-Zentrum Dresden-Rossendorf, and ICFO shows that weak magnetic fields applied perpendicular to the VSi symmetry axis invert the optically detected magnetic resonance (ODMR) contrast. This inversion is attributed to the reorientation of spin polarization, offering insights into spin dynamics and potential applications in quantum sensing and spin-photon interfaces.

We demonstrate twin-free epitaxial growth of rocksalt ScN on wurtzite GaN by using the two-fold symmetric M-plane surface of GaN, avoiding twinning issues. This enables high-quality integration of transition metal nitrides with III-nitrides, enhancing device performance and enabling new applications with additional functionalities like superconductivity and photonic resonances.

PDI researchers have discovered a novel modulation regime in semiconductor-based lasers, characterized by "acceleration beats". The universal effect, observed experimentally for the first time, suggests potential for new high-frequency spectral features and quantum control protocols, with implications extending to cosmic and high-energy particle phenomena.

An international research team led by Roman Engel-Herbert has reported previously unobserved phenomena in an ultra-clean sample of the correlated metal SrVO3. The study challenges existing theoretical models by providing new insights, suggesting a need to re-evaluate current theories on electron interactions. The breakthrough was achieved using an innovative growth technique, leading to the synthesis of SrVO3 with unprecedented purity, enabling detailed exploration of its true properties.

Researchers have observed a time crystal on a microscale semiconductor chip oscillating at a rate of several billion times per second, unveiling exceptionally high non-linear dynamics in the GHz range. The experiment results, published today in Science, establish a firm connection between formerly uncorrelated areas of non-linear exciton-polariton dynamics and coherent optomechanics at GHz frequencies.

An invited paper by PDI Senior Scientist Esperanza Luna Garcia de la Infanta was recently selected as Featured article (Journal Editors’ choice) in a special issue of the Journal of Applied Physics. The research conducted at PDI marks the second-ever published experimental confirmation of Bi_Ga hetero-antisites and provides a crucial step towards enhancing material quality and facilitating applications.

New research, led by a partnership between the Paul Drude Institute (PDI) and Penn State University, reveals surprising activity within an often overlooked material in computer chip design. This discovery has the potential to revolutionize electronics, leading to faster and more energy-efficient devices.

A recent paper published in Advanced Science and featuring contributions from PDI researchers demonstrated that molecular beam epitaxy allows fabricating lamellar GeTe-rich (GeTe)m(Sb2Te3)n alloys which show ferroelectric properties. The material was developed at PDI within the European project BeforeHand (GA 824957, Horizon2020) – a collaboration between PDI and six other European partners.

Two-dimensional (2D) magnetic materials are promising building blocks for the realization of novel, ultra-compact devices for spintronics. Combining them with other 2D crystals such as graphene is a very attractive route to realize hybrid material systems exhibiting integrated magnetic and electronic functionalities.

In a paper published recently in Advanced Science, researchers from the Paul Drude Institute in Berlin, Germany, and the Xiamen University, Xiamen, China, demonstrated that ferrimagnetic NiCo2O4 (NCO) constitutes a solution for the long-term challenge of finding materials with a robust out-of-plane magnetization.

Roman Engel-Herbert, Director of PDI, and Joao Marcelo J. Lopes, a Senior Scientist at PDI, were honored recently with an invitation to review the field of two-dimensional layered materials (2DLM) in a paper for ACS titled 'Recent Advances in 2D Material Theory, Synthesis, Properties, and Applications'.

GaAs-based nanowires are among the most promising candidates for realizing a monolithic integration of III-V optoelectronics on the Si platform. To realize their full potential for applications as light absorbers and emitters, it is crucial to understand their interaction with light governing the absorption and extraction efficiency, as well as the carrier recombination dynamics determining the radiative efficiency.

In a paper published today in Nature Communications, researchers from the Paul-Drude-Institut in Berlin, Germany, and the Instituto Balseiro in Bariloche, Argentina, demonstrated that the mixing of confined quantum fluids of light and GHz sound leads to the emergence of an elusive phonoriton quasi-particle – in part a quantum of light (photon), a quantum of sound (phonon) and a semiconductor exciton.

In this CReA we have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively.

A figure of merit for the potential performance of any bipolar semiconductor device is the carrier diffusion length. For the technologically secondmost relevant semiconductor GaN, popular ways to determine this quantity using cathodoluminescence (CL) have been found to be based on incomplete physical models. This background motivates us to take a fresh, in-depth look on how to determine the carrier diffusion length in GaN using CL spectroscopy.

Electrically driven, coherent phonons (sound waves in solids) with frequencies in the super-high-frequency (SHF) 3-30 GHz range are an important tool for the coherent manipulation of solid-state excitations. These phonons play a crucial role in optomechanics by enabling processes such as laser cooling of resonators to the mechanical ground state as well as in the quantum-coherent coupling between microwaves and near-infrared photons.

The correlation between the emission frequency and the location on the wafer due to an inhomogeneous growth rate across the wafer was investigated for GaAs/AlAs terahertz (THz) quantum-cascade lasers (QCLs) using experiments and simulations.

Lasing – the emission of a collimated light beam of light with a well-defined wavelength (color) and phase - results from a self-organization process, in which a collection of emission centers synchronizes itself to produce identical light particles (photons). A similar self-organized synchronization phenomenon can also lead to the generation of coherent vibrations – a phonon laser, where phonon denotes, in analogy to photons, the quantum particles of sound.

The progress of electronic devices is increasingly linked to the utilization of quantum effects. A future scenario are integrated quantum circuits containing coupled nanostructures. Interconnects, coupling distant on-chip components, could then be realized by the exchange of ballistic electrons. Our work aims at optimizing the coherent exchange of ballistic electrons between quantum point contacts, fundamental building blocks of quantum circuits.

Researchers from the Paul-Drude-Institut in Berlin, the Helmholtz-Zentrum in Dresden and the Ioffe Institute in St. Petersburg have demonstrated the use of elastic vibrations to manipulate the spin states of optically active color centers in SiC at room temperature.

Non-reciprocal propagation of sound is an essential requirement for the realization of devices such as acoustic isolators and circulators. Here, we demonstrate the efficient non-reciprocal transmission of surface acoustic waves propagating in a GaAs substrate coated with an epitaxial Fe3Si film.

A popular method to experimentally determine the diffusion length of minority carriers or excitons in semiconductors relies on the perception that threading dislocations are line defects that act as nonradiative sinks for carriers. The zone of reduced luminescence intensity around the dislocation is thus directly related to the carrier or exciton diffusion length.

Terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures have been developed for application-defined emission frequencies between 3.4 and 5.0 THz. These THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy.

Light emission centres in solids are promising candidates for applications in quantum information processing due to their capability of acting as single photon sources. One of the challenges related to these kinds of quantum light sources is to find mechanisms for the efficient control of their optoelectronic properties.

Interactions of light and material excitations (e.g., excitons) are at the heart of the modern and future optoelectronics. Efficient control and spatial localization (confinement) of the optical fields and particles is a crucial challenge.