A5089399403- GaN-based semiconductor devices and materials
- Semiconductor Quantum Structures and Devices
- Semiconductor materials and devices
- ZnO doping and properties
- Ga2O3 and related materials
- Semiconductor materials and interfaces
- Advancements in Semiconductor Devices and Circuit Design
- Electron and X-Ray Spectroscopy Techniques
- Advanced Semiconductor Detectors and Materials
- Advanced Electron Microscopy Techniques and Applications
- Acoustic Wave Resonator Technologies
- Advanced Photocatalysis Techniques
- Metal and Thin Film Mechanics
- Quantum and electron transport phenomena
- Nanowire Synthesis and Applications
- Integrated Circuits and Semiconductor Failure Analysis
- Electronic and Structural Properties of Oxides
- Surface and Thin Film Phenomena
- nanoparticles nucleation surface interactions
- Photonic and Optical Devices
- Ferroelectric and Piezoelectric Materials
- Multiferroics and related materials
- Semiconductor Lasers and Optical Devices
- Gold and Silver Nanoparticles Synthesis and Applications
- Intermetallics and Advanced Alloy Properties
Leibniz Institute for Crystal Growth
2013-2025
Friedrich-Alexander-Universität Erlangen-Nürnberg
1999-2009
Karlsruhe Institute of Technology
1997
In this paper, we employ in situ transmission electron microscopy to study the disorder–order phase transition from amorphous Ga2O3 γ-Ga2O3 and then β-Ga2O3. The studies are complemented by ex annealing experiments, of which results analyzed x-ray diffraction high resolution (scanning) microscopy. Amorphous deposited at 100 °C molecular beam epitaxy crystallizes 470 γ (Fd3̄m), undergoes a β above 500 °C. Between 500° 900 °C, find mixture β-Ga2O3 coexisting. Above 950 only Through our...
We have studied the electronic confinement in hexagonal (0001) $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ multiple quantum wells by means of structural (high-resolution x-ray diffraction and transmission electron microscopy) as well optical characterizations, namely intersubband absorption interband photoluminescence spectroscopies. Intense absorptions covering $1.33--1.91\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ wavelength range been measured on a series samples with...
We have studied the effect of growth and design parameters on performance Si-doped GaN/AlN multiquantum-well (MQW) structures for intersubband optoelectronics in near infrared. The samples under study display infrared absorption 1.3–1.9 μm wavelength range, originating from photoexcitation electrons first to second electronic level QWs. A commonly observed feature is presence multiple peaks both interband emission spectra, which are attributed monolayer thickness fluctuations quantum wells....
Heteroepitaxial Ga2O3 was grown on c-plane sapphire by molecular beam epitaxy, pulsed-laser deposition, and metalorganic chemical vapor deposition. Investigation scanning transmission electron microscopy (STEM) revealed the presence of a three-monolayer-thick pseudomorphically layer trigonal α-Ga2O3 at interface between substrate β-Ga2O3 independent growth method. On top this layer, plastically relaxed monoclinic grew in form rotational domains. We rationalize stable high-pressure α-phase...
We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. c direction. Atomic force microscopy layers substrates with miscut-angles smaller than 2° reveals proceeding through nucleation and two-dimensional islands. With increasing miscut-angle, step meandering finally flow take place. While step-flow results in high crystalline perfection, independent islands causes double positioning plane, resulting twin lamellae stacking...
The morphology evolution of (1 0 0) β-Ga2O3 films grown by metalorganic vapor phase epitaxy (MOVPE) is studied atomic force microscopy (AFM). In particular, when under a high O2/Ga ratio (O2/Ga = 1250) and above thickness 350 nm, these exhibit striking morphological instabilities, including step meandering bunching, which contribute significantly to surface roughening. Transmission electronic (TEM) measurements reveal transition on the growing with coexistence step-flow step-bunching growth...
Combining through-focus high-resolution transmission electron microscopy and hierarchical multiscale simulations consisting of density-functional theory, analytical empirical potentials, continuum elastic theory we demonstrate the existence a new dislocation type in GaN. In contrast with all previously identified or suggested structures GaN, core atoms are fully coordinated; i.e., no broken bonds occur, implying that should be electrically inactive. However, as show, giant local strain-field...
Combining aberration corrected high resolution transmission electron microscopy and density functional theory calculations we propose an explanation of the antisurfactant effect Si in GaN growth. We identify atomic structure a delta-doped layer (commonly called ${\mathrm{SiN}}_{x}$ mask) as ${\mathrm{SiGaN}}_{3}$ monolayer that resembles $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{ }R30\ifmmode^\circ\else\textdegree\fi{}$ surface reconstruction containing one atom, Ga vacancy...
We analyze the influence of annealing on compositional fluctuations in InGaAsN quantum wells by means composition-sensitive high-resolution transmission electron microscopy and photoluminescence. In as-grown samples, we find In-concentration ±5% a length scale 20 nm two-dimensional grown well. No indications for N concentration are found within limits resolution. Annealing homogenizes distribution well causes diffusion out According to our analysis, blueshift photoluminescence can part be...
We report on the controlled growth by molecular beam epitaxy of 20-period Si-doped GaN∕AlN quantum dot (QD) superlattices, in order to tailor their intraband absorption within 1.3–1.55μm telecommunication spectral range. The QD size can be tuned modifying amount GaN QDs, temperature, or interruption time (Ostwald ripening). By adjusting conditions, QDs with height (diameter) range 1–1.5nm (10–40nm), and density between 1011 1012cm−2 synthesized, fully strained AlN pseudosubstrate. To...
Room temperature intersubband electroabsorption modulation in GaN∕AlN coupled quantum wells is demonstrated at short infrared wavelengths, covering the fiber-optics telecommunication wavelength range. Electroabsorption with opposite sign observed λ=1.2–1.67μm and λ=2.1–2.4μm. The electromodulation originates from electron tunneling between a wide well (reservoir) narrow separated by an ultrathin AlN barrier. Both absorption spectroscopic measurements are good agreement simulations. maximum...
Epitaxially strained NaNbO 3 films were grown by liquid-delivery spin metal–organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently compressively NdGaO exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to monoclinic r and, further on, for under rare earth scandates, second aa phase, are observed. Our results in good...
We propose a method that solves the problem of independent determination indium and nitrogen concentrations in strained quaternary InGaAsN superlattice. The is experimentally based on simultaneous measurement: (i) tetragonal lattice distortion unit cell from high resolution micrographs (ii) intensity chemically sensitive (002) reflection dark field images. As an example, we evaluate quantum wells with nominal N concentration 1.7% In 10%, 20%, or 35%. reveal local fluctuations over distances...
The electron confinement in double GaN∕AlN quantum wells coupled by an ultrathin AlN barrier has been investigated means of structural and optical measurements. intersubband absorption spectra present two peaks attributed to the e1-e2 e1-e3 transitions, respectively. results photoluminescence spectroscopies are compared with simulations electronic structure based on envelope function formalism. A good agreement is obtained for all samples. These provide clear evidence that potential drop at...
We propose an approach that improves the measuring precision of lattice parameters in semiconductor alloys from high resolution transmission electron microscopy images on unit cell scale. The method is based evaluation a series taken under optimized imaging conditions aberration corrected microscope. By comparing image simulations with experimental images, we show hardly avoidable amorphous surface layers are main cause for limited precision. use our to analyze In distribution within nominal...
Abstract With comprehensive crystal growth experiments of β‐(Al x Ga 1‐x ) 2 O 3 by the Czochralski method this work concludes a maximum [Al] = 40 mol% (35 in melt) that can be incorporated into β‐Ga lattice while keeping single crystalline and monoclinic phase, resulting formula 0.4 0.6 . Transmission Electron Microscopy (TEM) analysis reveals random distribution Al across both octahedral tetrahedral sites. This has shown, incorporation only [Ga] ≥ 5 α‐Al crystals leads to phase separation...
The top‐seeded solution growth for rutile GeO 2 single crystals using alkali carbonates or fluorides as flux is applied. Structural data of obtained confirm the phase with a = b 4.3966 Å and c 2.8612 Å. diameter 5–15 mm are either undoped intentionally doped Sb 5+ , Sn 4+ Al 3+ Ga F − ions. It found that very efficient n‐type donor enabling free electron concentration even above 10 20 cm −3 ; thus, Sb‐doped potential substrate vertical power devices. In contrast, do not show p‐type...
It is shown that in GaN∕AlN multiple quantum wells (MQWs), strain a critical parameter for achieving short-wavelength intersubband transitions (ISBTs). This investigated by comparing MQWs grown metal organic vapor phase epitaxy on either AlN or GaN templates. The interface found to be unstable when pseudomorphically strained onto GaN, agreement with theory. effect deeply affects the well potential profile leading strong redshift of ISBT energies.
Results from a structural and optical analysis of buried InxGa1−xAs islands carried out after the process GaAs overgrowth are presented. It is found that during growth process, indium concentration profile changes thickness wetting layer emanating Stranski–Krastanow mode grows significantly. Quantum dots formed due to strong gradients in concentration, which demonstrated by photoluminescence excitation spectroscopy InInxGa1−xAs islands.
Lattice-parameter mismatch-induced strains in three-dimensional coherent InxGa1-xAs islands grown on GaAs(001) substrates have been determined experimentally an atomic scale by a digital analysis of images obtained high-resolution transmission electron microscopy. The strain distributions the were simulated finite-element calculations. are found to be good agreement with measured data, taking into account thin-foil relaxation electron-transparent specimens addition well known elastic relief....
In this article, we report on growth of AlInN∕GaInN multi-quantum-wells (MQWs) with high Al content (93%) by rf-plasma-assisted molecular-beam epitaxy (0001) GaN/sapphire templates and bulk GaN crystals. A series samples a barrier thickness 3nm different well thicknesses 1.5–3nm was grown. The wells were doped Si at concentration 5×1019cm−3. Structures grown GaN-based substrates are crack-free, as demonstrated Nomarski contrast scanning electron microscopy measurements. X-ray diffraction...
The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. analysis shows the upper (0001) boundary to consist a single Mg layer inserted between polarity inverted GaN layers an abcab stacking. bound these defects is at least one order magnitude lower than chemical concentration. Temperature dependent Hall effect measurements show that up 27% acceptors electrically compensated.