The demand for single photon sources at $λ~=~1.54~μ$m, which follows from the consistent development of quantum networks based on commercial optical fibers, makes Er:O$_x$ centers in Si still a viable resource thanks to the optical transition of $Er^{3+}~:~^4I_{13/2}~\rightarrow~^4I_{15/2}$. Yet, to date, the implementation of such system remains hindered by its extremely low emission rate. In this Letter, we explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of $Er:O_x$ in $Si$. The emitted photons, excited by a $λ~=~792~nm$ laser in both large areas and confined dots of diameter down to $5~μ$m, are collected by an inverted confocal microscope. The lower-bound number of detectable emission centers within our diffraction-limited illumination spot is estimated to be down to about 10$^4$, corresponding to an emission rate per individual ion of about $4~\times~10^{3}$ photons/s.
By coupling silicon nanowires (~150 nm diameter, 20 micron length) with an Ω-shaped plasmonic nanocavity we are able to generate broadband visible luminescence, which is induced by high-order hybrid nanocavity-surface plasmon modes. The nature of this super-bandgap emission is explored via photoluminescence spectroscopy studies performed with variable laser excitation energies (1.959 eV to 2.708 eV) and finite difference time domain simulations. Furthermore, temperature-dependent photoluminescence spectroscopy shows that the observed emission corresponds to radiative recombination of un-therma…
Nanocomposite films of Zinc Oxide and Silicon were grown by thermal evaporation technique using varying ratios of ZnO:Si in the starting material. Analysis reveal the role of ZnO and amorphous silicon interface in contributing to relatively less common blue photoluminescence emissions (at $\sim$ 400 and 470nm). These blue peaks are observed along with the emissions resulting from band edge transition (370nm) and those related to defects (522nm) of ZnO. Careful analysis shows that along with the grain size of ZnO, a suitable compositional ratio (of ZnO to silicon) is critical for the coexistenc…
Silicon carbide with optically and magnetically active point defects offers unique opportunities for quantum technology applications. Since interaction with these defects commonly happens through optical excitation and de-excitation, a complete understanding of their light-matter interaction in general and optical signatures, in particular, is crucial. Here, we employ quantum mechanical density functional theory calculations to investigate the photoluminescence lineshapes of selected, experimentally observed color centers (including single vacancies, double vacancies, and vacancy impurity pair…
We propose a new variety of silicon quantum dots containing fullerene-derived hollows of nearly arbitrary symmetry. Conglomerate structures are designed by connecting the quantum dots through two kinds of junctions. The quantum confinement effect is investigated using semiempirical quantum-mechanical method. It is shown that within each family of quantum dots, the band gap and the stability are inversely proportional to the particle effective size. Quantum dots inherit a wide variety of structural and symmetry properties from their parent fullerenes. The conglomerates confine electrons like qu…
The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here we present room temperature photoluminescence and ellipsometry measurements of Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the red shift of the room temperature near band gap emission from the Ga_{100%-x}Mn_{x}As alloy with increasing Mn content. It is shown that even a doping b…
Photoluminescence is observed at room temperature from phonon-assisted band-to-band emission in Si (1.067 eV peak) using unpatterned bulk p-type silicon wafer samples that were spin-coated with Er-doped (6 at. %) silica-gel films (0.13 micron) and vacuum annealed; the strongest emission was obtained at ~700 degrees C. Comparative study of annealing behavior indicates two-orders of magnitude efficiency enhancement. Emission from Er+3 ions in the silica film is used to gauge relative emission strengths. Mechanisms for inducing emission from silicon utilizing stresses in sol-gel-films are discuss…
An electron spin resonance (ESR) and photoluminescence signal is observed in the as grown single crystal of stishovite indicating the presence of defects in the non-irradiated sample. Photoluminescence of the as received stishovite single crystals exhibits two main bands - a blue at 3 eV and an UV at 4.75 eV. Luminescence is excited in the range of optical transparency of stishovite (below 8.75 eV) and, therefore, is ascribed to defects. A wide range of decay kinetics under a pulsed excitation is observed. For the blue band besides the exponential decay with a time constant of about 18 μs an a…
Ge-on-Si structures in-situ doped with phosphorus or arsenic via metal organic chemical vapor deposition (MOCVD) were investigated. Surface roughness, strain, threading dislocation desnity, Si-Ge interdiffusion, dopant diffusion, and photoluminescence were characterized to study the impacts of defect annealing and Si substrate offcut effects on the Ge film quality and most importantly, the light emission properties. All samples have a smooth surface (roughness < 1.5 nm), and the Ge films have a small tensile strain of 0.2%. As-grown P and As-doped Ge films have threading dislocaiton densities …
Multiscale Correlation of Morphological, Chemical, and Optical Properties in p-Type Porous Silicon
Escuela de Física and Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Sede Rodrigo Facio, Universidad de Costa Rica（哥斯达黎加大学物理学院与材料科学与工程研究中心（CICIMA），罗德里戈法西奥校区）
Compressive-Sensing-Enhanced First-Principles Calculation of Photoluminescence Spectra in Color Centers: A Comparison between Theory and Experiment for the G Center in Silicon
We generate silicon vacancy related defects in high-quality epitaxial silicon carbide layers by means of electron irradiation. By controlling the irradiation fluence, the defect concentration is varied over several orders of magnitude. We establish the excitation profile for optical pumping of these defects and evaluate the optimum excitation wavelength of 770 nm. We also measure the photoluminescence dynamics at room temperature and find a monoexponential decay with a characteristic lifetime of 6.1 ns. The integrated photoluminescence intensity depends linear on the excitation power density u…
We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies ($V_{\mathrm{Si}}$) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 $μ$s. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altoget…
Photoluminescence of Femtosecond Laser-irradiated Silicon Carbide
RPTU University Kaiserslautern-Landau（凯泽斯劳滕-兰道莱布尼茨技术大学）；Universität des Saarlandes（萨尔兰州立大学）；Luxembourg Institute of Science and Technology (LIST)（卢森堡科学与技术研究所）；University of Luxembourg（卢森堡大学）；Institut für Oberflächen- und Schichttechnik GmbH（表面与薄膜技术研究所有限公司）
Prior studies have shown that photoluminescence from Er3+ impurities in silicon is severely limited at room temperature by non-radiative relaxation and solid solubility; and room temperature emission from Er3+ in oxide-based hosts becomes diminished at high erbium concentrations. This work presents studies of thin films (0.2 micron thick) prepared by vacuum co-evaporation from elemental sources (Er, Si and Si/Ge) followed by vacuum annealing (600 degrees C); materials of this type, which are produced with high Er3+ concentrations, are shown to be capable of yielding strong room-temperature pho…
We measured the temperature dependence of photoluminescence involved with the metastability of unintentionally doped GaN. Reaction energy U of donor atom is 0.1eV and shallow donor is more stable than deep center. The impurity transition was applied to unintentionally doped GaN at low temperature and reaction energy U was provided for shallow-deep transition. We propose that the origin of DX center in unintentionally doped wurtize GaN is considered to be an oxygen impurity instead of silicon.
The effect of alloy disorder on the optical density of states and the average room temperature carrier statistics in GaInNAs quantum wells is discussed. A red shift between the peak of the room temperature photoluminescence and the surface photovoltage spectra, that systematically increases with the nitrogen content within the quantum wells is observed. The relationship between this Stokes' shift and the absorption linewidth in different samples suggests that the photoexcited carriers undergo a continuous transition, from being in quasi-thermal equilibrium with the lattice to being completely …
Metal/semiconductor hybrids are artificially created structures presenting novel properties not exhibited by either of the component materials alone. Here we present a giant piezoresistance effect in a hybrid formed from silicon and aluminum. The maximum piezoresistive gage factor (GF) of 843, measured at room temperature, compares with a GF of -93 measured in the bulk homogeneous silicon. This piezoresistance boost is not due to the silicon/aluminum interface, but results from a stress induced anisotropy in the silicon conductivity that acts to switch current away from the highly conductive a…
Identification of microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, still two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] a…
The compositional dependence of the lowest direct and indirect band gaps in $\text{Ge}_{1-y}\text{Sn}_{y}$ has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration $y_{c}$ at which the alloy becomes a direct gap semiconductor. For the di…
The photoluminescence and spin properties of ensembles of color centers in silicon carbide are enhanced by fabricating optically isolated slab waveguide structures and carefully controlling annealing and cooling conditions. We find that the photoluminescence signal of an ensemble of implanted defects is enhanced in slab waveguides by an order of magnitude over identically implanted bulk defects. The slab waveguide-enhanced photoluminescence of several defect species is used to study recombination and diffusion in the presence of thermal annealing with both rapid quench cooling and a longer ret…
Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The transmission electron microscopy studies evidenced the substantial accumulation of Mn inside the catalyzing Ga droplets at the top of the nanowires. Optical and transport measurements revealed that the limit of Mn content for self-catalysed growth of GaAs nanowires corresponds to the doping level, i.e., is mu…
We report the first observation of stable single photon sources in silicon carbide (SiC). These sources are extremely bright and operate at room temperature demonstrating that SiC is a viable material in which to realize various quantum information, computation and photonic applications. The maximum single photon count rate detected is 700k counts/s with an inferred quantum efficiency around 70%. The single photon sources are due to intrinsic deep level defects constituted of carbon antisite-vacancy pairs. These are shown to be formed controllably by electron irradiation. The variability of th…
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
Nanocomposite thin films of Zinc Oxide and Silicon were grown by co-evaporating powdered ZnO and Si. This resulted in nanocrystallites of ZnO being embedded in Silicon. The mismatch in crystal structures of constituent materials result in the ZnO nanocrystals to exist in a state of stress. This along with oxygen vacancies in the samples result in good Photoluminescence emission at 520nm. Also, Silicon background gave a photoluminescence emission at 620nm. The structure was found quite stable over time since the homgenously dispersed ZnO nanocrystals do not agglomerate. The nanocomposites promi…
The study of hexagonal silicon polytypes attracts special attention due to their unique physical properties compared to the traditional cubic phase of Si. Thus, for some hexagonal phases, a significant improvement in the emission properties has been demonstrated. In this work, the luminescent properties of SiO2/Si structures irradiated with Kr+ ions at different doses and annealed at 800 °C have been systematically investigated. For such structures, a photoluminescence line at ~ 1240 nm is observed and associated with the formation of hexagonal 9R-Si phase inclusions. It is found that the vari…
Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in visi…
Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irra…
BaMnF$_4$ microsheets have been prepared by hydrothermal method. Strong room-temperature blue-violet photoluminescence has been observed (absolute luminescence quantum yield 67%), with two peaks located at 385 nm and 410 nm, respectively. More interestingly, photon self-absorption phenomenon has been observed, leading to unusual abrupt drop of luminescence intensity at wavelength of 400 nm. To understand the underlying mechanism of such emitting, the electronic structure of BaMnF$_4$ has been studied by first principles calculations. The observed two peaks are attributed to electrons' transiti…
Silicon-vacancy (SiV) centers in diamond are promising systems for quantum information applications due to their bright single photon emission and optically accessible spin states. Furthermore, SiV centers in low-strain diamond are insensitive to pertubations of the dielectric environment, i.e. they show very weak spectral diffusion. This property renders ensembles of SiV centers interesting for sensing applications. We here report on photoluminescence excitation (PLE) spectroscopy on an SiV ensemble in a low strain, CVD-grown high quality diamond layer, where we measure the fine structure wit…
Temperature dependent photoluminescence (PL) is used to study the electronic properties of single CdS nanowires. At low temperatures, both near-band edge (NBE) photoluminescence (PL) and spatially-localized defect-related PL are observed in many nanowires. The intensity of the defect states is a sensitive tool to judge the character and structural uniformity of nanowires. As the temperature is raised, the defect states rapidly quench at varying rates leaving the NBE PL which dominates up to room temperature. All PL lines from nanowires follow closely the temperature-dependent band edge, simila…
The study of defect centers in silicon has been recently reinvigorated by their potential applications in optical quantum information processing. A number of silicon defect centers emit single photons in the telecommunication $O$-band, making them promising building blocks for quantum networks between computing nodes. The two-carbon G-center, self-interstitial W-center, and spin-$1/2$ T-center are the most intensively studied silicon defect centers, yet despite this, there is no consensus on the precise configurations of defect atoms in these centers, and their electronic structures remain amb…
We demonstrate a silicon-based high frequency nanomechanical device capable of switching controllably between two states at room temperature. The device uses a nanomechanical resonator with two distinct states in the hysteretic nonlinear regime. In contrast to prior work, we demonstrate room temperature electrostatic actuation and sensing of the switching device with 100% fidelity by phase modulating the drive signal. This phase-modulated device can be used as a low-power high-speed mechanical switch integrated on-chip with silicon circuitry.
We report on photoluminescence in the 3-7 $μ$m mid-wave infrared (MWIR) range from sub-100 nm strained thin films of rocksalt PbSe(001) grown on GaAs(001) substrates by molecular beam epitaxy. These bare films, grown epitaxially at temperatures below 400 °C, luminesce brightly at room temperature and have minority carrier lifetimes as long as 172 ns. The relatively long lifetimes in PbSe thin films are achievable despite threading dislocation densities exceeding $10^9$ $cm^{-2}$ arising from island growth on the nearly 8% lattice- and crystal-structure-mismatched GaAs substrate. Using quasi-co…
Monolayer transition metal dichalcogenides (TMDs) show an optimal surface-to-volume ratio and are thus promising candidates for novel molecule sensor devices. It was recently predicted that a certain class of molecules exhibiting a large dipole moment can be detected through the activation of optically inaccessible (dark) excitonic states in absorption spectra of tungsten-based TMDs. In this work, we investigate the molecule signatures in photoluminescence spectra in dependence of a number of different experimentally accessible quantities, such as excitation density, temperature as well as mol…
By means of ab-initio calculations we investigate the optical properties of pure a-SiN$_x$ samples, with $x \in [0.4, 1.8]$, and samples embedding silicon nanoclusters (NCs) of diameter $0.5 \leq d \leq 1.0$ nm. In the pure samples the optical absorption gap and the radiative recombination rate vary according to the concentration of Si-N bonds. In the presence of NCs the radiative rate of the samples is barely affected, indicating that the intense photoluminescence of experimental samples is mostly due to the matrix itself rather than to the NCs. Besides, we evidence an important role of Si-N-…
The negatively charged silicon vacancy ($\mathrm{V_{Si}^-}$) in silicon carbide is a well-studied point defect for quantum applications. At the same time, a closer inspection of ensemble photoluminescence and electron paramagnetic resonance measurements reveals an abundance of related but so far unidentified signals. In this study, we search for defects in 4H-SiC that explain the above magneto-optical signals in a defect database generated by Automatic Defect Analysis and Qualification (ADAQ) workflows. This search reveals only one class of atomic structures that exhibit silicon-vacancy-like p…
Improvement of the photovoltaic efficiency (from 1.2% to 3%) via exposure of organic poly(3-hexylthiophene) (P3HT) + phenyl-C61-butyric acid methyl ester (PCBM) devices to solvent vapor at room temperature is reported. In situ photoluminescence (PL) and Raman spectroscopies, in conjunction with optical absorption data, have been used to provide insight into the nanoscale morphological changes occurring during solvent vapor annealing. We found that in P3HT:PCBM, suppression of PL and the decrease in line-width of the 1442 cm-1 P3HT Raman peak are accompanied by strong modifications in the optic…
The band structure of MoS$_2$ strongly depends on the number of layers, and a transition from indirect to direct-gap semiconductor has been observed recently for a single layer of MoS$_2$. Single-layer MoS$_2$ therefore becomes an efficient emitter of photoluminescence even at room temperature. Here, we report on scanning Raman and on temperature-dependent, as well as time-resolved photoluminescence measurements on single-layer MoS$_2$ flakes prepared by exfoliation. We observe the emergence of two distinct photoluminescence peaks at low temperatures. The photocarrier recombination at low temp…
Defects ~10 nm in size, with number densities ~10^{10} cm^{-2}, form spontaneously beneath ion-milled, etched, or HF-dipped silicon surfaces examined in our Ti-ion getter-pumped transmission electron microscope (TEM) after exposure to air. They appear as weakly-strained non-crystalline intrusions into silicon bulk, that show up best in the TEM under conditions of strong edge or bend contrast. If ambient air exposure is <10 minutes, defect nucleation and growth can be monitored {\em in situ}. Possible mechanisms of formation are discussed.
The "textbook" phonon mean free path (MFP) of heat carrying phonons in silicon at room temperature is ~40 nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer MFPs. We present a simple experiment demonstrating that room temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal gr…
The use of cryogenic silicon as a detector medium for dark matter searches is gaining popularity. Many of these searches are highly dependent on the value of the photoelectric absorption cross section of silicon at low temperatures, particularly near the silicon band gap energy, where the searches are most sensitive to low mass dark matter candidates. While such cross section data has been lacking from the literature, previous dark matter search experiments have attempted to estimate this parameter by extrapolating it from higher temperature data. However, discrepancies in the high temperature…
The decay of the optical phonon into the two phonons of smaller energy is calculated for Si nanocrystals. The rate of the process is in the range of 1 to 10 ps. Such anharmonic phonon decay may control the energy relaxation rate of excited carriers in Si/SiO$_2$ nanocrystals. Relevance of the phonon decay to the experimentally observed hot carrier photoluminescence is discussed.
Er-doped aluminum nitride films, containing different Er concentrations, were obtained at room temperature by reactive radio frequency magnetron sputtering. The prepared samples show a nano-columnar microstructure and the size of the columns is dependent on the magnetron power. The Er-related photoluminescence (PL) was studied in relation with the temperature, the Er content and the microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved PL were performed. Both visible and near infrared PL were obtained at room temperature for the as-deposited samples. It is demonstrated …
To augment the magnetoresistance (MR) ratio of n-type non-degenerate Si-based lateral spin valves (Si-LSVs), we modify the doping profile in the Si layer and introduce a larger local strain into the Si channel by changing a capping insulator. The highest MR ratio of 1.4% is achieved in the Si-LSVs through these improvements, with significant roles played by a reduction in the resistance-area product of the ferromagnetic contacts and an enhancement of the momentum relaxation time in the Si channel.
The silicon-vacancy (SiV) center in diamond is typically found in three stable charge states, SiV0, SiV- and SiV2-, but studying the processes leading to their formation is challenging, especially at room temperature, due to their starkly different photo-luminescence rates. Here, we use confocal fluorescence microscopy to activate and probe charge interconversion between all three charge states under ambient conditions. In particular, we witness the formation of SiV0 via the two-step capture of diffusing, photo-generated holes, a process we expose both through direct SiV0 fluorescence measurem…
It is shown for the first time, that room temperature Ultrasonic Defect Manipulation (UDM) can significantly reduce the concentration of radiation defects in high resistivity silicon. Secondary Ion Mass Spectroscopy revealed that oxygen- and hydrogen- related chemical reactions in silicon are likely to occur under UDM at room temperature. Ultrasonically stimulated chemical reactions in solids can be an important source of energy, which is required for UDM.
Single photon emitters (SPEs) play an important role in a number of quantum information tasks such as quantum key distributions. In these protocols, telecom wavelength photons are desired due to their low transmission loss in optical fibers. In this paper, we present a study of bright single-photon emitters in cubic silicon carbide (3C-SiC) emitting in the telecom range. We find that these emitters are photostable and bright at room temperature with a count rate of ~ MHz. Together with the fact that SiC is a growth and fabrication-friendly material, our result may pave the way for its future a…
We demonstrate spin-accumulation signals controlled by the gate voltage in a metal-oxide-semiconductor field effect transistor structure with a Si channel and a CoFe/$n^{+}$-Si contact at room temperature. Under the application of a back-gate voltage, we clearly observe the three-terminal Hanle-effect signal, i.e., spin-accumulation signal. The magnitude of the spin-accumulation signals can be reduced with increasing the gate voltage. We consider that the gate controlled spin signals are attributed to the change in the carrier density in the Si channel beneath the CoFe/$n^{+}$-Si contact. This…
Using a metal-oxide-semiconductor field effect transistor (MOSFET) structure with a high-quality CoFe/n^+Si contact, we systematically study spin injection and spin accumulation in a nondegenerated Si channel with a doping density of ~ 4.5*10^15cm^-3 at room temperature. By applying the gate voltage (V_G) to the channel, we obtain sufficient bias currents (I_Bias) for creating spin accumulation in the channel and observe clear spin-accumulation signals even at room temperature. Whereas the magnitude of the spin signals is enhanced by increasing I_Bias, it is reduced by increasing V_G interesti…
Silicon films doped with Er and O were prepared by techniques of physical vapor deposition on crystalline silicon, ion beam mixing and oxygen incorporation through Ar+ and O2+ implantation, and thermal annealing. Processing steps were tailored to be compatible with standard CMOS and to be of notably low cost to fabricate optically active media for silicon-based infrared emitters. The Si:Er:O films exhibit strong photoluminescence at room temperature that is analogous to Stark-split Er+3 ion 1.55-micron bands in fiber-optic materials. Concentration distributions were determined by Rutherford ba…
