In this article, the results of investigation of processes occurring during the molecular-beam deposition of germanium layers on Si$_3$N$_4$ dielectric substrates within a wide range of the Ge film growth temperatures (30 to 600°C) are presented. The intensity of the IR absorption bands related to the vibrations of the N$-$H and Si$-$N bonds are established to decrease with the increase of the Ge deposition temperature. It appears that this phenomenon cannot be explained only as a thermally activated process. Simultaneously, the peak corresponding to the Ge$-$N vibration bonds emerges in the X-ray photoelectron spectra. We suppose that the deposition of germanium layers on Si3N4 dielectric substrates containing hydrogen atoms causes the diffusion of hydrogen atoms from the dielectric layer into the growing film. The experimental results may be interpreted in terms of a model, according to which the migration of hydrogen atoms from the Si$_3$N$_4$ layer into the growing germanium film is due to the difference in chemical potentials of hydrogen atoms in the dielectric layer and the germanium film. This process initiates the diffusion of germanium atoms in the opposite direction, into the Si$_3$N$_4$ layer, where they connect to free bonds of nitrogen atoms arising due to the escape of hydrogen atoms. The analogous processes occur during the deposition of silicon layers on Si$_3$N$_4$ substrates.
The dynamics of the luminescence decay from germanium nanocrystals embedded in crystalline silicon has been studied for temperatures varied between 16 K and room temperature. At room temperature the characteristic decay time is of the order of 50 nanoseconds while it extends into the microsecond range at low temperatures. The decay is dominated by non-radiative processes, which show a typical thermal activation energy of a few meV.
The lifting of the two-fold degeneracy of the conduction valleys in a strained silicon quantum well is critical for spin quantum computing. Here, we obtain an accurate measurement of the splitting of the valley states in the low-field region of interest, using the microwave spectroscopy technique of electron valley resonance (EVR). We compare our results with conventional methods, observing a linear magnetic field dependence of the valley splitting, and a strong low-field suppression, consistent with recent theory. The resonance linewidth shows a marked enhancement above $T\simeq 300$ mK.
We present a first-principles study of bare and hydrogen passivated armchair nanoribbons of the puckered single layer honeycomb structures of silicon and germanium. Our study includes optimization of atomic structure, stability analysis based on the calculation of phonon dispersions, electronic structure and the variation of band gap with the width of the ribbon. The band gaps of silicon and germanium nanoribbons exhibit family behavior similar to those of graphene nanoribbons. The edges of bare nanoribbons are sharply reconstructed, which can be eliminated by the hydrogen termination of dangl…
The thermal coefficient of resistance (TCR) for epitaxial silicon-germanium (SiGe) layers has been analyzed by experiment and simulation. Predictive simulation using drift-diffusion formalism and self-consistent quantum-mechanical solutions yielded similar results, TCR around 2%/K at 300 K. This modeling approach can be used for different, graded and constant, SiGe profiles,. It is also capable of predicting the influence of background auto-doping on the TCR of the detectors
Hall-effect and magnetoresistivity of holes in silicon and germanium are considered with due regard for mutual drag of light and heavy band carriers. Search of contribution of this drag shows that this interaction has a sufficient and non-trivial influence on both effects.
Compared with direct-gap semiconductors, the valley degeneracy of silicon and germanium opens up new channels for spin relaxation that counteract the spin degeneracy of the inversion-symmetric system. Here the symmetries of the electron-phonon interaction for silicon and germanium are identified and the resulting spin lifetimes are calculated. Room-temperature spin lifetimes of electrons in silicon are found to be comparable to those in gallium arsenide, however, the spin lifetimes in silicon or germanium can be tuned by reducing the valley degeneracy through strain or quantum confinement. The…
In this work we report new silicon and germanium tubular nanostructures with no corresponding stable carbon analogues. The electronic and mechanical properties of these new tubes were investigated through ab initio methods. Our results show that the structures have lower energy than their corresponding nanoribbon structures and are stable up to high temperatures (500 and 1000 K, for silicon and germanium tubes, respectively). Both tubes are semiconducting with small indirect band gaps, which can be significantly altered by both compressive and tensile strains. Large bandgap variations of almos…
The mechanism responsible for the emission of clusters from heavy ion irradiated solids is proposed to be thermal spikes. Collision cascade-based theories describe atomic sputtering but cannot explain the consistently observed experimental evidence for significant cluster emission. Statistical thermodynamic arguments for thermal spikes are employed here for qualitative and quantitative estimation of the thermal spike-induced cluster emission from silicon, germanium and zinc oxide. The evolving cascades and spikes in elemental and molecular semiconducting solids are shown to have fractal charac…
We report the fabrication and electrical characterization of a single electron transistor in a modulation doped silicon/silicon-germanium heterostructure. The quantum dot is fabricated by electron beam lithography and subsequent reactive ion etching. The dot potential and electron density are modified by laterally defined side gates in the plane of the dot. Low temperature measurements show Coulomb blockade with a single electron charging energy of 3.2 meV.
We report on the growth and characterization of Ge-doped \b{eta}-Ga2O3 thin films using a solid germanium source. \b{eta}-Ga2O3 thin films were grown using a low-pressure chemical vapor deposition (LPCVD) reactor with either an oxygen or gallium delivery tube. Films were grown on 6 degree offcut sapphire and (010) \b{eta}-Ga2O3 substrates with growth rates between 0.5 - 22 μm/hr. By controlling the germanium vapor pressure, a wide range of Hall carrier concentrations between 10^17 - 10^19 cm-3 were achieved. Low-temperature Hall data revealed a difference in donor incorporation depending on th…
The universal building block which is an essential part of all atomic structures on (1 1 0) silicon and germanium surfaces and their vicinals is proposed from first-principles calculations and a comparison of results with available experimental data. The atomic models for the (1 1 0)-(16x2), (1 1 0)-c(8x10), (1 1 0)-(5x8) and (17 15 1)-(2x1) surface reconstructions are developed on the basis of the building block structure. The models exhibit very low surface energies and excellent agreements with bias-dependent scanning tunneling microscopy (STM) images. It is shown experimentally using STM t…
Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic-scale devices using donor atoms as qubits have largely focussed on phosphorus in silicon. Positioning phosphorus in silicon with atomic-scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale-up to large-scale devices. Here, we present a comprehensive study of arsine (AsH$_3$) on the germ…
Core-shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core-shell nanowires aligned along the $[110]$ direction, with diameters up to 10.2~nm and varying core to shell ratios, using linear scaling Density Functional Theory (DFT). We show that Vegard's law, which is often used to predict the axial lattice constant, can lead to an error of up to 1\%, underlining the need for a detailed \emph{ab initio} atomistic treatment of the nanowire structure. We analys…
We present ab initio calculations of the electronic and optical properties of hexagonal SiGe alloys in the lonsdaleite structure. Lattice constants and electronic band structures in excellent agreement with experiment are obtained using density-functional theory. Hexagonal Si has an indirect band gap, while hexagonal Ge has a pseudo-direct gap, i.e. the optical transitions at the minimum direct band gap are very weak. The pseudo-direct character of pure hexagonal Ge is efficiently lifted by alloying. Already for a small admixture of Si, symmetry reduction enhances the oscillator strength of th…
This article continues our recent publication [I.A. Baburin and D.M. Proserpio and V.A. Saleev and A.V. Shipilova, Phys. Chem. Chem. Phys.17, 1332 (2015)] where we have presented a comprehensive computational study of sp3 carbon allotropes based on the topologies proposed for zeolites. Here we predict six new silicon and six new germanium allotropes which have the same space group symmetries and topologies as those predicted earlier for the carbon allotropes, and study their structural, elastic, vibrational, electronic and optical properties.
A 2D layer of spherical, crystalline Ge nanodots embedded in SiO2 was formed by low pressure chemical vapour deposition combined with furnace oxidation and rapid thermal annealing. The samples were characterized structurally by using transmission electron microscopy and rutherford back scattering spectrometry, as well as electrically by measuring CV and IV characteristics. It was found that formation of a high density Ge dots took place due to oxidation induced Ge segregation. The dots are situated in the SiO2 on the average distance 5 nm from the substrate. Strong evidence of charge storage e…
We demonstrate high-quality epitaxial germanium (Ge) films on a metallic silicide, Fe3Si, grown directly on a Ge(111) substrate. Using molecular beam epitaxy techniques, we can obtain an artificially controlled arrangement of silicon (Si) or iron (Fe) atoms at the surface on Fe3Si(111). The Si-terminated Fe3Si(111) surface enables us to grow two-dimensional epitaxial Ge films, whereas the Fe-terminated one causes the three-dimensional epitaxial growth of Ge films. The high-quality Ge grown on the Si-terminated surface has almost no strain, meaning that the Ge films are not grown on the low-tem…
Implicit summation is a technique for the conversion of sums over intermediate states in multiphoton absorption and the high-order susceptibility in hydrogen into simple integrals. Here, we derive the equivalent technique for hydrogenic impurities in multi-valley semiconductors. While the absorption has useful applications, it is primarily a loss process; conversely, the non-linear susceptibility is a crucial parameter for active photonic devices. For Si:P, we predict the hyperpolarizability ranges from $χ^{(3)}/n_{\text{3D}}=2.9 $ to $580 \times 10^{-38}$ $\text{m}^5/\text{V}^2$ depending on …
Conductivity of p-Si and p-Ge is considered for two band model with due regard for mutual drag of light and heavy holes. It is shown that for small and moderate temperatures this drag significantly diminishes drift velocity of light holes and, as result, the total conductivity of crystal. Considered here drag-effect appears as well in the form of nonmonotonous dependences of conductivity on temperature and carrier density.
Based on first-principles calculations of structure optimization, phonon modes and finite temperature molecular dynamics, we predict that silicon and germanium have stable, two-dimensional, low-buckled, honeycomb structures. Similar to graphene, they are ambipolar and their charge carriers can behave like a massless Dirac fermions due to their pi- and pi*-bands which are crossed linearly at the Fermi level. In addition to these fundamental properties, bare and hydrogen passivated nanoribbons of Si and Ge show remarkable electronic and magnetic properties, which are size and orientation depende…
A theoretical modeling of the oxygen diffusivity in silicon and germanium crystals both at normal and high hydrostatic pressure has been carried out using molecular mechanics, semiempirical and ab initio methods. It was established that the diffusion process of an interstitial oxygen atom (Oi) is controlled by the optimum configuration of three silicon (germanium) atoms nearest to Oi. The calculated values of the activation energy Ea(Si)= 2.59 eV, Ea(Ge)= 2.05 eV and pre-exponential factor Do (Si) = 0.28 sm2 s-1, Do (Ge) = 0.39 sm2 s-1 are in a good agreement with experimental ones and for the…
Hexagonal group IV materials like silicon and germanium are expected to display remarkable optoelectronic properties for future development of photonic technologies. However, the fabrication of hexagonal group IV semiconductors within the vapour-liquid-solid method has been obtained using gold as a catalyst thus far. In this letter, we show the synthesis of hexagonal Ge on self-assisted GaAs nanowires using molecular beam epitaxy. With an accurate tuning of the Ga and As molecular beam flux we selected the crystal phase, cubic or hexagonal, of the GaAs NWs during the growth. A 500 nm-long hexa…
Germanium and silicon-germanium alloys have found entry into Si technology thanks to their compatibility with Si processing and their ability to tailor electronic properties by strain and band-gap engineering. Germanium's potential to extend Si functionalities, as exemplified by lasing action of strained-Ge on Si substrates, has brought the material back to attention. Yet despite these advances, non-radiative transitions, induced by crystal defects originating from the Ge/Si interface, continue to be a serious bottleneck. Here we demonstrate the drastic emission enhancement achieved via contro…
Temperature effects on the energetics of the 90-degree partial dislocation in silicon and germanium are investigated, using non-equilibrium methods to estimate free energies, coupled with Monte Carlo simulations. Atomic interactions are described by Tersoff and EDIP interatomic potentials. Our results indicate that the vibrational entropy has the effect of increasing the difference in free energy between the two possible reconstructions of the 90-degree partial, namely, the single-period and the double-period geometries. This effect further increases the energetic stability of the double-perio…
Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/S…
Semiconductor superlattices have been extensively investigated for thermoelectric applications, to explore the effects of compositions, interface structures, and lattice strain environments on the reduction of thermal conductivity, and improvement of efficiency. Most studies assumed that their electronic properties remain unaffected compared to their bulk counterparts. However, recent studies demonstrated that electronic properties of silicon (Si)/germanium (Ge) superlattices show significant variations depending on compositions and growth substrates. These studies used a constant relaxation t…
We discuss a model for the on-site matrix elements of the sp3d5s* tight-binding hamiltonian of a strained diamond or zinc-blende crystal or nanostructure. This model features on-site, off-diagonal couplings between the s, p and d orbitals, and is able to reproduce the effects of arbitrary strains on the band energies and effective masses in the full Brillouin zone. It introduces only a few additional parameters and is free from any ambiguities that might arise from the definition of the macroscopic strains as a function of the atomic positions. We apply this model to silicon, germanium and the…
Germanium-Tin is emerging as a material exhibiting excellent photonic properties. Here we demonstrate optical initialization and readout of spins in this intriguing group IV semiconductor alloy and report on spin quantum beats between Zeeman-split levels under an external magnetic field. Our optical experiments reveal robust spin orientation in a wide temperature range and a persistent spin lifetime that approaches the ns regime at room temperature. Besides important insights into nonradiative recombination pathways, our findings disclose a rich spin physics in novel epitaxial structures direc…
We present a comprehensive theory of the circularly polarized luminescence and its dependence on strain in spin-polarized Si and Ge. Symmetries of wavefunctions and interactions are used to derive concise ratios between intensities of the right and left circularly polarized luminescence for each of the dominant phonon-assisted optical transitions. These ratios are then used to explain the circular polarization degrees of the luminescence peaks in the spectra of biaxially-strained Si and Ge, and of relaxed ${\rm{Si}}_{1-x}{\rm{Ge}}_{x}$ alloys. The spectra are numerically calculated by a combin…
We have investigated the structural sequence of the high-pressure phases of silicon and germanium. We have focussed on the cd->beta-tin->Imma->sh phase transitions. We have used the plane-wave pseudopotential approach to the density-functional theory implemented within the Vienna ab-initio simulation package (VASP). We have determined the equilibrium properties of each structure and the values of the critical parameters including a hysteresis effect at the phase transitions. The order of the phase transitions has been obtained alternatively from the pressure dependence of the enthalpy and of t…
In a semiconductor heterostructure with type II energy band alignment, the spatial separation between electrons and holes slows down their radiative recombination. With increasing excitation intensity, Auger recombination quickly becomes the dominate recombination channel, and it produces carrier ejection from the quantum well. Here, we show that in Si/SiGe three-dimensional nanostructures, this efficient process facilitates the formation of an electron-hole plasma (EHP) and/or electron-hole droplets (EHDs) in thin Si barriers separating SiGe clusters. In contrast to conventional, strongly tem…
For Si and Ge nanocrystals (NCs) embedded in wide band-gap matrices, Auger recombination (AR) and carrier multiplication (CM) lifetimes are computed exactly in a three-dimensional real space grid using empirical pseudopotential wave functions. Our results in support of recent experimental data offer new predictions. We extract simple Auger constants valid for NCs. We show that both Si and Ge NCs can benefit from photovoltaic efficiency improvement via CM due to the fact that under an optical excitation exceeding twice the band gap energy, the electrons gain lion's share from the total excess e…
Depth-Resolved Lattice Distortions in a Silicon-Germanium Qubit Host
Q-NEXT, Argonne National Laboratory（Q-NEXT，阿贡国家实验室）；Materials Science Division, Argonne National Laboratory（材料科学部，阿贡国家实验室）；Pritzker School of Molecular Engineering, University of Chicago（普里茨克分子工程学院，芝加哥大学）；Department of Physics, University of Wisconsin-Madison（物理学系，威斯康星大学麦迪逊分校）；Center for Nanoscale Materials, Argonne National Laboratory（纳米材料中心，阿贡国家实验室）
Electrical properties of multilayer arrays of germanium nanoclusters grown on the silicon (001) surface at low temperature have been studied. A correlation between the quantum dot (QD) density estimated from STM and the charge accumulated by QD layers as extracted from C-V characteristics was revealed. Temperature dependence of the C-V characteristics was studied. At low temperatures, the hysteresis was observed. DLTS spectra measured on the structures with different QD arrangements demonstrated essential distinctions.
Special point defects in semiconductors have been envisioned as suitable components for quantum-information technology. The identification of new deep centers in silicon that can be easily activated and controlled is a main target of the research in the field. Vacancy-related complexes are suitable to provide deep electronic levels but they are hard to control spatially. With the spirit of investigating solid state devices with intentional vacancy-related defects at controlled position, here we report on the functionalization of silicon vacancies by implanting Ge atoms through single-ion impla…
We calculate the thermoelectric figure of merit, zT=S^2GT/(κ_l+κ_e), for p-type Si nanowires with axial Ge heterostructures using a combination of first-principles density-functional theory, interatomic potentials, and Landauer-Buttiker transport theory. We consider nanowires with up to 8400 atoms and twelve Ge axial heterostructures along their length. We find that introducing heterostructures always reduces S^2G, and that our calculated increases in zT are predominantly driven by associated decreases in κ_l. Of the systems considered, <111> nanowires with a regular distribution of Ge heteros…
Two-dimensional (2D) ferromagnetic materials have been exhibiting promising potential in applications, such as spintronics devices. To grow epitaxial magnetic films on silicon substrate, in the single-layer limit, is practically important but challenging. In this study, we realized the epitaxial growth of MnSn monolayer on Si(111) substrate, with an atomically thin Sn/Si(111)-$2\sqrt{3}\times2\sqrt{3}$- buffer layer, and controlled the MnSn thickness with atomic-layer precision. We discovered the ferromagnetism in MnSn monolayer with the Curie temperature (Tc) of ~54 K. As the MnSn film is gro…
The precise knowledge of the atomic order in monocrystalline alloys is fundamental to understand and predict their physical properties. With this perspective, we utilized laser-assisted atom probe tomography to investigate the three-dimensional distribution of atoms in non-equilibrium epitaxial Sn-rich group IV SiGeSn ternary semiconductors. Different atom probe statistical analysis tools including frequency distribution analysis, partial radial distribution functions, and nearest neighbor analysis were employed in order to evaluate and compare the behavior of the three elements to their spati…
Searches for low-energy tetrahedral polymorphs of carbon and silicon have been performed using density functional theory computations and the ab initio random structure searching (AIRSS) ap- proach. Several of the hypothetical phases obtained in our searches have enthalpies that are lower or comparable to those of other polymorphs of group 14 elements that have either been experimentally synthesized or recently proposed as the structure of unknown phases obtained in experiments, and should thus be considered as particularly interesting candidates. A structure of P bam symmetry with 24 atoms in…
The theoretical analysis of the process of diffusion of interstitial oxygen atoms and hydrogen molecules in silicon and germanium crystals has been performed. The calculated values of the activation energy and pre-exponential factor for an interstitial oxygen atom Ea(Si) = 2.59 eV, Ea(Ge) = 2.05 eV, D(Si)= 0.28 cm2s-1, D(Ge)= 0.39 cm2s-1 and interstitial hydrogen molecule Ea(Si) = 0.79-0.83 eV, Ea(Ge) = 0.58-0.62 eV, D(Si)= 7.4 10(-4) cm2s-1, D(Ge)= 6.5 10(-4) cm2s-1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature depen…
While several 2D thermometry techniques exist, there is a lack of 3D thermometry techniques that work for wide range of materials and offer good resolution in time, space and temperature. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) imaging can provide 3D temperature information. However, XRD is typically limited to crystalline materials while NMR is largely limited to liquids where the resonance lines are narrow. We investigate electron paramagnetic resonance (EPR) of n-type silicon and germanium for 3D thermometry. While in germanium the EPR linewidths are too broad, EPR line…
Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first principles
Epitaxial graphene films were grown in vacuo by silicon sublimation from the (0001) and (000-1) faces of 4H- and 6H-SiC. Hall effect mobilities and sheet carrier densities of the films were measured at 300 K and 77 K and the data depended on the growth face. About 40% of the samples exhibited holes as the dominant carrier, independent of face. Generally, mobilities increased with decreasing carrier density, independent of carrier type and substrate polytype. The contributions of scattering mechanisms to the conductivities of the films are discussed. The results suggest that for near-intrinsic …
In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in …
Extending chip performance beyond current limits of miniaturisation requires new materials and functionalities that integrate well with the silicon platform. Germanium fits these requirements and has been proposed as a high-mobility channel material,[1] a light emitting medium in silicon-integrated lasers,[2,3] and a plasmonic conductor for bio-sensing.[4,5] Common to these diverse applications is the need for homogeneous, high electron densities in three-dimensions (3D). Here we use a bottom-up approach to demonstrate the 3D assembly of atomically sharp doping profiles in germanium by a repea…
Czochralski-grown boron-doped silicon crystals were studied by the techniques of the low-angle mid-IR-light scattering and electron-beam-induced current. The large-scale accumulations of electrically-active impurities detected in this material were found to be different in their nature and formation mechanisms from the well-known impurity clouds in a float zone-grown silicon. A classifcation of the large-scale impurity accumulations in CZ Si:B is made and point centers constituting them are analyzed in this paper. A model of the large-scale impurity accumulations in CZ-grown Si:B is also propo…
We present a contactless method for measuring charge in a thin film of amorphous germanium (a-Ge) with a nanoscale silicon MOSFET charge sensor. This method enables the measurement of conductance of the a-Ge film even in the presence of blocking contacts. At high bias voltage, the resistance of the contacts becomes negligible and a direct measurement of current gives a conductance that agrees with that from the measurement of charge. This charge-sensing technique is used to measure the temperature- and field-dependence of the conductance, and they both agree with a model of Mott variable-range…
It was previously believed that the Bloch electronic states of non-magnetic materials with inversion symmetry cannot have finite spin polarizations. However, since the seminal work by Zhang et al. [Nat. Phys. 10, 387-393 (2014)] on local spin polarizations of Bloch states in non-magnetic, centrosymmetric materials, the scope of spintronics has been significantly broadened. Here, we show, using a framework that is universally applicable independent of whether hidden spin polarizations are small (e.g., diamond, Si, Ge, and GaAs) or large (e.g., MoS2 and WSe2), that the corresponding quantity ari…
We report the growth of InAs$_{1-x}$Sb$_{x}$ nanowires ($0\leq x \leq 0.15$) grown by catalyst-free molecular beam epitaxy on silicon (111) substrates. We observed a sharp decrease of stacking fault density in the InAs$_{1-x}$Sb$_{x}$ nanowire crystal structure with increasing antimony content. This decrease leads to a significant increase in the field-effect mobility, this being more than three times greater at room temperature for InAs$_{0.85}$Sb$_{0.15}$ nanowires than InAs nanowires.
Silicon-based quantum bits with electron spins in quantum dots or nuclear spins on dopants are serious contenders in the race for quantum computation. Added to process integration maturity, the lack of nuclear spins in the most abundant $^{28}$silicon isotope host crystal for qubits is a major asset for this silicon quantum technology. We have grown $^{28}$silicon epitaxial layers (epilayers) with an isotopic purity greater than 99.992 % on 300mm natural abundance silicon crystals. The quality of the mono-crystalline isotopically purified epilayer conforms to the same drastic quality requireme…
We compare the temperature dependence of optical and electrical characteristics of commercially available GaN light-emitting diodes (LEDs) grown on silicon and sapphire substrates. Contrary to conventional expectations, LEDs grown on silicon substrates, commonly referred to as GaN-on-Si LEDs, show less efficiency droop at higher temperatures even with more threading dislocations. Analysis of the junction temperature reveals that GaN-on-Si LEDs have a cooler junction despite sharing identical epitaxial structures and packaging compared to LEDs grown on sapphire substrates. We also observe a dec…
Commonly, germanium crystals are grown after the Czochralski (CZ) method. The crucible-free pedestal and floating zone (FZ) methods, which are widely used for silicon growth, are hardly known to be investigated for germanium. The germanium melt is more than twice as dense as liquid silicon, which could destabilize a floating zone. Additionally, the lower melting point and the related lower radiative heat loss is shown to reduce the stability especially of the FZ process with the consequence of a screw-like crystal growth. We found that the lower heat radiation of Ge can be compensated by the i…
Room-temperature quantum oscillations of static magnetic susceptibility of silicon-carbide epitaxial layers grown on a silicon substrate by the method of the coordinated substitution of atoms
Czochralski-grown silicon crystals were studied by the techniques of the low-angle mid-IR-light scattering and electron-beam-induced current. The large-scale accumulations of electrically-active impurities detected in this material were found to be different in their nature and formation mechanisms from the well-known impurity clouds in a FZ-grown silicon. A classification of the large-scale impurity accumulations in CZ Si is made and point centers constituting them are analyzed in this paper. A model of the large-scale impurity accumulations in CZ-grown Si is also proposed. In addition, the i…
