Jan Beyer

TU Bergakademie Freiberg

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Johannes Heitmann

TU Bergakademie Freiberg

Richard Gloaguen

Helmholtz Institute Freiberg for Resource Technology

I. A. Buyanova

Linköping University

Weimin Chen

Linköping University

S. Suraprapapich

University of California, San Diego

Margret Fuchs

Helmholtz-Zentrum Dresden-Rossendorf

Suchinder K. Sharma

Helmholtz Institute Freiberg for Resource Technology

Sandra Lorenz

Helmholtz-Zentrum Dresden-Rossendorf

C. W. Tu

University of California, San Diego

C. W. Tu

Research Center for Applied Science, Academia Sinica

Cooperative Institutions

TU Bergakademie Freiberg

Helmholtz-Zentrum Dresden-Rossendorf

Helmholtz Institute Freiberg for Resource Technology

TU Dresden

Poznań University of Technology

Leibniz Institute for Solid State and Materials Research

Linköping University

Fraunhofer Institute for Integrated Systems and Device Technology

University of California, San Diego

Chemnitz University of Technology

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Size and Shape Controlled Semiconductor Nanocrystals Synthesized by RF‐Sputtering Techniques for Electronic and Optoelectronic Applications

Contributions to Plasma Physics (2015)

David Lehninger Jan Beyer F. Schneider A.‐S. Pawlik J. Heitmann

Abstract Group IV (Ge and Si) nanocrystals embedded in a dielectric matrix were prepared via rf magnetron sputtering by the deposition of superlattices of stoichiometric and substoichiometric oxide layers and subsequent annealing. By this way Ge nanocrystals in a (Ta)ZrO x and Si nanocrystals in an SiO 2 matrix were prepared in a size and shape controlled manner. In case of the Ge‐ZrO 2 system, elongated Ge nanocrystals in a crystallized ZrO 2 matrix were formed for annealing temperatures above 660 °C. Starting from a Si 3 N 4 interface of the Si wafer, a preferential orientation between the Ge and ZrO 2 lattice can be stated. Doping the ZrO 2 matrix additionally with Ta increases the crystallization temperature of the ZrO 2 matrix and leads to the formation of Ge nanocrystals embedded in an amorphous TaZrO x matrix. The Ge nanocrystals were investigated by photoluminescence measurements and implemented into metal‐insulator‐semiconductor capacitor to investigate their potential for charge trapping devices. The prepared nano floating gate devices show good charging characteristics with a maximum memory window of 5 V and a slope of the writing voltage vs. memory window characteristics of 0.8‐1. All luminescence centers seen in the Ge‐(Ta)ZrO x system can be attributed to defects either from the Ge nanocrystal surface, the (Ta)ZrO x matrix or the Si substrate itself. Si nanocrystals were fabricated in the same way in an amorphous SiO 2 film after annealing above 900 °C. The formed Si nanocrystals act as superior sensitizer for Er 3+ ions which were ion implanted into the films followed by an additional subsequent anneal, varied between 700 and 1000 °C. The Si nanocrystal ‐ Er 3+ system was successfully implemented into a slot waveguide structure showing a strong polarization dependent field enhancement in both emission and excitation geometry. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

10.1002/ctpp.201510017

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A Review on Ge Nanocrystals Embedded in SiO₂ and High‐k Dielectrics

physica status solidi (a) (2018)

David Lehninger Jan Beyer Johannes Heitmann

In this article, the work on Ge nanocrystals embedded in dielectric films formed by phase separation from supersaturated solid solutions is reviewed. Different methods to synthesize supersaturated solid solutions are covered, e.g., magnetron sputtering, ion implantation, and chemical vapor deposition. The phase separation is activated by subsequent high temperature annealing. Important parameters that influence the formation and properties of the Ge nanocrystals are discussed. Various matrix materials like SiO 2 , Al 2 O 3 , HfO 2 , HfAlO x , Lu 2 O 3 , ZrO 2 , TaZrO x , and Si 3 N 4 are reported in the literature. The influence of the matrix on the formation and properties of the Ge nanocrystals is addressed in this review. Ge nanocrystals are investigated for applications such as charge storage nodes in nonvolatile memory devices or as silicon technology compatible light emitters. A key to establish these applications seems to be embedding the Ge nanocrystals in still amorphous matrices. This could help to avoid grain boundaries that act as leakage paths for electrical charges (unfavorable for nonvolatile memories) and facilitate defects, which could act as recombination centers (unfavorable for light emitters). A further important point is the synthesis of size and position controlled Ge nanocrystals. Both aspects are reviewed for Ge nanocrystals embedded in the mentioned matrix materials.

10.1002/pssa.201701028

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Citations (44)

Laser-induced fluorescence mapping: a new spectroscopic technique for detection of Rare Earth Elements in rock samples

EGUGA (2019)

Peter Seidel Sandra Lorenz Margret Fuchs Robert Zimmermann René Booysen

Earth observation

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Erbium-doped slot waveguides containing size-controlled silicon nanocrystals

Journal of Applied Physics (2015)

Raik Hoffmann Jan Beyer V. Klemm David Rafaja Brett C. Johnson

Silicon based slot waveguides with a slot containing Si nanocrystals (Si-nc) and Erbium ions (Er3+) inside a silica matrix were prepared using sputter deposition and low-energy ion implantation. This sequence enabled independent optimization of nanocrystal formation and Er3+ incorporation parameters. Using a superlattice approach, the size of the Si-nc inside the slot could be controlled and optimized for maximum Er3+ luminescence yield at 1.54 μm. Er3+ is found to be efficiently pumped by Si-nc of sizes around 3 to 4 nm. Increasing Er3+ photoluminescence at 1.54 μm with increasing post-implantation annealing temperatures up to 1000 °C is attributed to annealing of matrix or Si-nc interface defects mainly. Additionally, a dependence of the Er3+ luminescence intensity on both the excitation and emission linear polarization orientation is shown, which demonstrates efficient field enhancement in sputtered slot waveguide structures.

Erbium

10.1063/1.4919420

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Temperature dependence of dynamic nuclear polarization and its effect on electron spin relaxation and dephasing in InAs/GaAs quantum dots

Applied Physics Letters (2012)

Jan Beyer Yuttapoom Puttisong I. A. Buyanova S. Suraprapapich C. W. Tu

Electron spin dephasing and relaxation due to hyperfine interaction with nuclear spins is studied in an InAs/GaAs quantum dot ensemble as a function of temperature up to 85 K, in an applied longitudinal magnetic field. The extent of hyperfine-induced dephasing is found to decrease, whereas dynamic nuclear polarization increases with increasing temperature. We attribute both effects to an accelerating electron spin relaxation through phonon-assisted electron-nuclear spin flip-flops driven by hyperfine interactions, which could become the dominating contribution to electron spin depolarization at high temperatures.

Dephasing

10.1063/1.3701273

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Citations (6)

Library of UV-Visible Absorption Spectra of Rare Earth Orthophosphates, LnPO4 (Ln = La-Lu, except Pm)

Crystals (2020)

Suchinder K. Sharma Thomas Behm T. Köhler Jan Beyer Richard Gloaguen

In recent times, rare earth orthophosphates ( L n PO 4 ) have shown great potential as efficient optical materials. They possess either m o n a z i t e or x e n o t i m e –type structures. These light or heavy rare earth bearing orthophosphates also exhibit an extraordinary stability over geological time scale in nature, ∼10 9 years. In the present contribution, we measure, collect, and present a library of absorption spectra of all the L n PO 4 hosts ( L n = La–Lu, except Pm) using their single crystal samples, to conclude that the observed spectral features for wavelengths longer than 200 nm were attributable to either Ln- or defect related centers, which corroborate the fact that they have a bandgap higher than 8.0 eV. The absorption band around wavelength, 275 nm, corresponds to defect absorption related to PO 3 centers and/or oxygen vacancies. The hosts can potentially be used to study and interpret unperturbed rare earth emissions due to absence of host related absorption above 300 nm. The information presented herein is expected to serve as a library of absorption spectra for geologists, physicists, material scientists, and chemists working in the field of rare earths.

Absorption band

Crystal (programming language)

10.3390/cryst10070593

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Citations (11)

Hanle effect in InAs/GaAs quantum dots up to room temperatures

Nanotechnology (2011)

Jan Beyer I. A. Buyanova S. Suraprapapich C. W. Tu Weimin Chen

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Dynamics of Charges in Superlong Blacklight-Emitting CaB₂O₄:Ce³⁺ Persistent Phosphor

The Journal of Physical Chemistry (2019)

Suchinder K. Sharma Marco Bettinelli I. Carrasco Jan Beyer Richard Gloaguen

The optical and persistent luminescence properties of CaB₂O₄:Ce³⁺ phosphor are presented. The optical emission for excitation in the 250–340 nm wavelength region is dominated by two bands at 365 and 460 nm. Lifetime measurements suggested that the 365 nm emission band is due to interconfigurational Ce³⁺ 5d → 4f transitions. Upon excitation with a 254 nm UV lamp, a superlong persistent luminescence in the UVA1 region (340–400 nm, blacklight) was observed, lasting for at least 15 h, and with excellent reproducibility, which is perfectly suitable for phototherapy application. The initial-rise method was applied on the thermoluminescence glow curves to determine the trap distribution and trap depth. The results suggest that one distinct trap, with an activation energy of ∼0.52 eV, was solely responsible for the persistent luminescence in the CaB₂O₄:Ce³⁺ phosphor. The other traps had a quasi-continuous distribution, with activation energies between 0.56 and 1.15 eV. The proposed persistent luminescence and the thermoluminescence mechanisms are elucidated using experimental parameters obtained from the optical and thermoluminescence results and the theoretically calculated electronic structure of the Ce³⁺ ion in CaB₂O₄. The lowest Ce³⁺ 5d₁ level was found to be ∼0.97 eV below the conduction band, and the persistent luminescence/thermoluminescence emission was dominated by the radiative transitions between Ce³⁺ energy levels, 5d → ²F₅/₂,₇/₂.

Persistent luminescence

Optically stimulated luminescence

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Line-scan detection system to identify rare earth elements in rocks

IEEE Sensors (2019)

Titus Abend Suchinder K. Sharma Margret Fuchs Jan Beyer J. Heitmann

We develop an integrated sensor system to detect rare earth elements (REE) in natural minerals on-site. The system combines reflectance and photoluminescence (PL) spectroscopy in order to present a noninvasive alternative to conventional time-consuming and costly chemical analysis of drill cores in mineral exploration. The major benefit lies in the rapid gathering of continuous spatial information on the type and abundance of the REEs in drill cores. Additionally the sample material remains unharmed during the whole process. To maximise scan speed and sample throughput, our system operates in continuous line scan mode, with continuous sample flow beneath the detector.

Sample (material)

10.1109/sensors43011.2019.8956697

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Free-carriers beat excitons in spin-injection contest

Jan Beyer I. A. Buyanova S. Suraprapapich C. W. Tu Weimin Chen

Quantum dots (QDs) are a promising building block for future spin-functional devices with applications in spintronics and quantum information processing. Essential to the success of these devices i ...

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CONTEST

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