WorldCat Identities

Jokubavicius, Valdas

Overview
Works: 18 works in 19 publications in 1 language and 20 library holdings
Roles: Author, Contributor
Publication Timeline
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Most widely held works by Valdas Jokubavicius
The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy by Symposium G EMRS 2013 Spring Meeting( )

2 editions published in 2014 in English and held by 3 WorldCat member libraries worldwide

Donor-acceptor co-doped SiC is a promising light converter for novel monolithic all-semiconductor white LEDs due to its broad-band donor-acceptor pair luminescence and potentially high internal quantum efficiency. Besides sufficiently high doping concentrations in an appropriate ratio yielding short radiative lifetimes, long nonradiative lifetimes are crucial for efficient light conversion. The impact of different types of defects is studied by characterizing fluorescent silicon carbide layers with regard to photoluminescence intensity, homogeneity and efficiency taking into account dislocation density and distribution. Different doping concentrations and variations in gas phase composition and pressure are investigated
Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface by David J Christle( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects
Sublimation growth of thick freestanding 3C-SiC using CVD-templates on silicon as seeds by Philip Hens( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

Energy levels and charge state control of the carbon antisite-vacancy defect in 4H-SiC by Son Tien Nguyen( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The carbon antisite-vacancy pair (CSiVC) in silicon carbide (SiC) has recently emerged as a promising defect for applications in quantum communication. In the positive charge state, CSiVC+ can be engineered to produce ultrabright single photon sources in the red spectral region, while in the neutral charge state, it has been predicted to emit light at telecom wavelengths and to have spin properties suitable for a quantum bit. In this electron paramagnetic resonance study using ultrapure compensated isotope-enriched 4H-(SiC)-Si-28, we determine the (+|0) level of CSiVC and show that the positive and neutral charge states of the defect can be optically controlled
A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates by Yuchen Shi( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

We present a comparative study of the C-face and Si-face of 3C-SiC(111) grown on off-oriented 4H-SiC substrates by the sublimation epitaxy. By the lateral enlargement method, we demonstrate that the high-quality bulk-like C-face 3C-SiC with thickness of ~1 mm can be grown over a large single domain without double positioning boundaries (DPBs), which are known to have a strongly negative impact on the electronic properties of the material. Moreover, the C-face sample exhibits a smoother surface with one unit cell height steps while the surface of the Si-face sample exhibits steps twice as high as on the C-face due to step-bunching. High-resolution XRD and low temperature photoluminescence measurements show that C-face 3C-SiC can reach the same high crystalline quality as the Si-face 3C-SiC. Furthermore, cross-section studies of the C- and Si-face 3C-SiC demonstrate that in both cases an initial homoepitaxial 4H-SiC layer followed by a polytype transition layer are formed prior to the formation and lateral expansion of 3C-SiC layer. However, the transition layer in the C-face sample is extending along the step-flow direction less than that on the Si-face sample, giving rise to a more fairly consistent crystalline quality 3C-SiC epilayer over the whole sample compared to the Si-face 3C-SiC where more defects appeared on the surface at the edge. This facilitates the lateral enlargement of 3C-SiC growth on hexagonal SiC substrates
Fluorescent silicon carbide as an ultraviolet-to-visible light converter by control of donor to acceptor recombinations by Xuefei( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

As an alternative to the conventional phosphors in white LEDs, a donor and acceptor co-doped fluorescent 6H-SiC can be used as an ultraviolet-to-visible light converter without any need of rare-earth metals. From experimental data we provide an explanation to how light can be obtained at room temperature by a balance of the donors and acceptors. A steady-state recombination rate model is used to demonstrate that the luminescence in fluorescent SiC can be enhanced by controlling the donor and acceptor doping levels. A doping criterion for optimization of this luminescence is thus proposed
Wafer Scale Growth and Characterization of Edge Specific Graphene Nanoribbons for Nanoelectronics by Alexei Zakharov( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

One of the ways to use graphene in field effect transistors is to introduce a band gap by quantum confinement effect. That is why narrow graphene nanoribbons (GNRs) with width less than 50 nm are considered to be essential components in future graphene electronics. The growth of graphene on sidewalls of SiC(0001) mesa structures using scalable photolithography was shown to produce high quality GNRs with excellent transport properties. Such epitaxial graphene nanoribbons are very important in fundamental science but if GNRs are supposed to be used in advanced nanoelectronics, high quality thin (<50 nm) nanoribbons should be produced on a large (wafer) scale. Here we present a technique for scalable template growth of high quality GNRs on Si-face of SiC(0001) and provide detailed structural information along with transport properties. For the first time we succeeded now to avoid SiC-facet instabilities in order to grow high quality GNRs along both [11̅00] and [112̅0] crystallographic directions on the same substrate. The quality of the grown nanoribbons was confirmed by comprehensive characterization with atomic resolution STM, dark field LEEM, and transport measurements. This approach generates an entirely new platform for both fundamental and application driven research of quasi one-dimensional carbon based magnetism and spintronics
White Light Emission from Fluorescent SiC with Porous Surface by Weifang Lu( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

We report for the first time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fluorescent SiC) layer containing a hybrid structure. The surface of fluorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20 nm thick Al2O3, the photoluminescence intensity from the porous layer was significant enhanced by a factor of more than 12. Using a porous layer of moderate thickness (similar to 10 mu m), high-quality white light emission was realized by combining the independent emissions of blue-green emission from the porous layer and yellow emission from the bulk fluorescent SiC layer. A high color rendering index of 81.1 has been achieved. Photoluminescence spectra in porous layers fabricated in both commercial n-type and lab grown N-B co-doped 6H-SiC show two emission peaks centered approximately at 460 nm and 530 nm. Such blue-green emission phenomenon can be attributed to neutral oxygen vacancies and interface C-related surface defects generated dring anodic oxidation process. Porous fluorescent SiC can offer a great flexibility in color rendering by changing the thickness of porous layer and bulk fluorescent layer. Such a novel approach opens a new perspective for the development of high performance and rare-earth element free white light emitting materials
Nanoporous Cubic Silicon Carbide Photoanodes for Enhanced Solar Water Splitting by Jingxin Jian( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

Cubic silicon carbide (3C-SiC) is a promising photoelectrode material for solar water splitting due to its relatively small band gap (2.36 eV) and its ideal energy band positions that straddle the water redox potentials. However, despite various coupled oxygen-evolution-reaction (OER) cocatalysts, it commonly exhibits a much smaller photocurrent (<similar to 1 mA cm(-2)) than the expected value (8 mA cm(-2)) from its band gap under AM1.5G 100 mW cm(-2) illumination. Here, we show that a short carrier diffusion length with respect to the large light penetration depth in 3C-SiC significantly limits the charge separation, thus resulting in a small photocurrent. To overcome this drawback, this work demonstrates a facile anodization method to fabricate nanoporous 3C-SiC photoanodes coupled with Ni:FeOOH cocatalyst that evidently improve the solar water splitting performance. The optimized nanoporous 3C-SiC shows a high photocurrent density of 2.30 mA cm(-2) at 1.23 V versus reversible hydrogen electrode (V-RHE) under AM1.5G 100 mW cm(-2) illumination, which is 3.3 times higher than that of its planar counterpart (0.69 mA cm(-2) at 1.23 V-RHE). We further demonstrate that the optimized nanoporous photoanode exhibits an enhanced light-harvesting efficiency (LHE) of over 93%, a high charge-separation efficiency (Phi(sep)) of 38%, and a high charge-injection efficiency (Phi(ox)) of 91% for water oxidation at 1.23 V-RHE, which are significantly outperforming those its planar counterpart (LHE = 78%, Phi(sep) = 28%, and Phi(ox) = 53% at 1.23 V-RHE). All of these properties of nanoporous 3C-SiC enable a synergetic enhancement of solar water splitting performance. This work also brings insights into the design of other indirect band gap semiconductors for solar energy conversion
An adhesive bonding approach by hydrogen silsesquioxane for silicon carbide-based LED applications by Li Lin( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

We report an adhesive bonding approach using hydrogen silsesquioxane (HSQ) for silicon carbide (SiC) samples. A hybrid light-emitting diode (LED) was successfully fabricated through bonding a near-ultraviolet (NUV) LED grown on a commercial 4H-SiC substrate to a free-standing boron-nitrogen co-doped fluorescent-SiC epi-layer. The bonding quality and the electrical performance of the hybrid LED device were characterized. Neither voids nor defects were observed which indicates a good bonding quality of the proposed HSQ approach. A strong warm white emission was successfully obtained from the hybrid LED through an electric current injection of 30 mA
Ligand hyperfine interactions at silicon vacancies in 4H-SiC by Son Tien Nguyen( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The negative silicon vacancy (V-Si( - )) in SiC has recently emerged as a promising defect for quantum communication and room-temperature quantum sensing. However, its electronic structure is still not well characterized. While the isolated Si vacancy is expected to give rise to only two paramagnetic centers corresponding to two inequivalent lattice sites in 4H-SiC, there have been five electron paramagnetic resonance (EPR) centers assigned to V-Si( - ) in the past: the so-called isolated no-zero-field splitting (ZFS) V-Si( - ) center and another four axial configurations with small ZFS: T-V1a, T-V2a, T-V1b, and T-V2b. Due to overlapping with Si-29 hyperfine (hf) structures in EPR spectra of natural 4H-SiC, hf parameters of T-V1a have not been determined. Using isotopically enriched 4H-(SiC)-Si-28, we overcome the problems of signal overlapping and observe hf parameters of nearest C neighbors for all three components of the S = 3/2 T-V1a and T-V2a centers. The obtained EPR data support the conclusion that only T-V1a and T-V2a are related to V-Si( - ) and the two configurations of the so-called isolated no-ZFS V-Si( - ) center, V-Si( - ) (I) and V-Si( - ) (II), are actually the central lines corresponding to the transition I-1/2 amp;lt;-amp;gt; I + 1/2 of the T-V2a and T-V1a centers, respectively
Shockley-Frank stacking faults in 6H-SiC by Xuefei( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

We report on Shockley-Frank stacking faults (SFs) identified in 6H-SiC by a combination of low temperature photoluminescence (LTPL) and high resolution transmission electron microscopy (TEM). In the faulted area, stacking faults manifested as large photoluminescence emissions bands located in between the 6H-SiC signal (at <".99 eV) and the 3C-SiC bulk-like one (at <".39 eV). Each of the stacking fault related emission band had a four-fold structure coming from the TA, LA, TO, and LO phonon modes of 3C-SiC. Up to four different faults, with four different thickness of the 3C-SiC lamella, could be observed simultaneously within the extent of the laser excitation spot. From the energy of the momentum-conservative phonons, they were associated with excitonic energy gaps at E gx 1 = 2.837 eV, E gx 2 = 2.689 eV, E gx 3 = 2.600 eV and E gx 4 = 2.525 eV. In the same part where low temperature photoluminescence was performed, high resolution transmission electron microscopy measurements revealed stacking faults which, in terms of the Zhdanov notation, could be recognized as SFs (3, 4), (3, 5), (3, 6), (3, 7), (3, 9), (3, 11), (3, 16) and (3, 22), respectively. Among them stacking fault (3, 4) was the most common one, but a faulted region with a (4, 4) 8H-SiC like sequence was also found. Using a type II 6H/3C/6H quantum-well model and comparing with experimental results, we find that the photoluminescence emissions with excitonic band gaps at 2.837 eV (E gx 1), 2.689 eV (E gx 2), 2.600 eV (E gx 3) and 2.525 eV (E gx 4) come from SFs (3, 4), (3, 5), (3, 6) and (3, 7), respectively. A possible formation mechanism of these SFs is suggested, which involves a combination of Frank faults with Shockley ones. This provides a basic understanding of stacking faults in 6H-SiC and gives a rapid and non-destructive approach to identify SFs by low temperature photoluminescence
Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures by Yiyu Ou( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

We demonstrate a time-efficient and low-cost approach to fabricate Si 3 N 4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si 3 N 4 coating are formed via dry etching and thin film deposition process. By using this method, a significant broadband surface antireflection and a considerable omnidirectional luminescence enhancement are obtained. The experimental observations are then supported by numerical simulations. It is believed that our fabrication method will be well suitable for large-scale production in the future
New Approaches and Understandings in the Growth of Cubic Silicon Carbide by Francesco La Via( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

In this review paper, several new approaches about the 3C-SiC growth are been presented. In fact, despite the long research activity on 3C-SiC, no devices with good electrical characteristics have been obtained due to the high defect density and high level of stress. To overcome these problems, two different approaches have been used in the last years. From one side, several compliance substrates have been used to try to reduce both the defects and stress, while from another side, the first bulk growth has been performed to try to improve the quality of this material with respect to the heteroepitaxial one. From all these studies, a new understanding of the material defects has been obtained, as well as regarding all the interactions between defects and several growth parameters. This new knowledge will be the basis to solve the main issue of the 3C-SiC growth and reach the goal to obtain a material with low defects and low stress that would allow for realizing devices with extremely interesting characteristics
Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111) by Yuchen Shi( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3C SiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3C SiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3C SiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed
Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates by Valdas Jokubavicius( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

Geometrical Control of 3C and 6H-SiC Nucleation on Low Off-Axis Substrates by Valdas Jokubavicius( )

1 edition published in 2011 in English and held by 1 WorldCat member library worldwide

Growth of 3C or 6H-SiC epilayers on low off-axis 6H-SiC substrates can be mastered by changing the size of the on axis plane formed by long terraces in the epilayer using geometrical control. The desired polytype can be selected in thick (~200 µm) layers of both 6H-SiC and 3C-SiC polytypes on substrates with off-orientation as low as 1.4 and 2 degrees. The resultant crystal quality of the 3C and the 6H-SiC epilayers, grown under the same process parameters, deteriorates when lowering the off-orientation of the substrate
Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum by Valdas Jokubavicius( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

We demonstrate growth of thick SiC layers (100-200 µm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10 −5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 µm/h and 70 µm/h for 6H- and 4H-SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C-SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 µm thick homoepitaxial 6H-SiC layer co-doped with nitrogen and boron in a range of 10 18 cm −3 at a growth rate of about 270 µm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer
 
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English (19)