Silicon-based Optoelectronics Research Articles

Tuning of SiO2/Si interface by a hybrid plasma process combining oxidation and atom-migration

As a common oxide-semiconductor interface, SiO2/Si plays an important role in silicon-based electronics and optoelectronics. In order to effectively obtain an ultra-smooth and thin SiO2/Si interface, a hybrid tuning process based on inductively coupled plasma (ICP) was proposed, which combined oxidation (plasma-OX) and atom-migration manufacturing (plasma-AMM). In plasma-OX process, a thick oxide film was rapidly prepared on Si wafer surface in 2 min, which included a SiO2 layer on the top and a SiOx (x < 2) layer between the top layer and the bulk crystalline silicon (c-Si). In subsequent plasma-AMM process, ICP steadily delivered energy to the Si wafer surface and induced the migration of unsaturated Si from SiOx layer to c-Si, which enhanced the crystallization of silicon wafer. The roughness of SiO2/Si interface was reduced to Sa 0.171 nm at 620 W in 5 min. However, a 2–3 nm thickness SiOx layer still existed, and several defects causing by residual thermal stress can be observed. Further optimizing plasma-AMM process by setting multi-step slow cooling, the SiOx layer can be almost completely decomposed. The interface roughness Sa was reduced to <0.1 nm and the interface thickness was reduced to 1–2 atom layer. Both OX and AMM process were conducted in the same setup, which is convenient for switching. This study proposed and demonstrated the feasibility of a hybrid plasma tuning process, which provided an efficient tuning technology at atomic level for semiconductor interface.

Neuromorphic Photonics Based on Phase Change Materials.

Neuromorphic photonics devices based on phase change materials (PCMs) and silicon photonics technology have emerged as promising solutions for addressing the limitations of traditional spiking neural networks in terms of scalability, response delay, and energy consumption. In this review, we provide a comprehensive analysis of various PCMs used in neuromorphic devices, comparing their optical properties and discussing their applications. We explore materials such as GST (Ge2Sb2Te5), GeTe-Sb2Te3, GSST (Ge2Sb2Se4Te1), Sb2S3/Sb2Se3, Sc0.2Sb2Te3 (SST), and In2Se3, highlighting their advantages and challenges in terms of erasure power consumption, response rate, material lifetime, and on-chip insertion loss. By investigating the integration of different PCMs with silicon-based optoelectronics, this review aims to identify potential breakthroughs in computational performance and scalability of photonic spiking neural networks. Further research and development are essential to optimize these materials and overcome their limitations, paving the way for more efficient and high-performance photonic neuromorphic devices in artificial intelligence and high-performance computing applications.

Luminescence of modified W-centers arising in silicon upon irradiation of the SiO2/Si system by Kr+ ions

Possible nature of photoluminescence (PL) at 1240 nm revealed in silicon coated with a SiO2 film and then irradiated with Kr+ followed by annealing at 800 °C has been discussed. The spectral position of the PL is close to that of well-known W-centers, but their features are essentially different: the detected PL line retains at higher annealing temperatures and experiences lower thermal quenching. Such modification of properties of W-centers (three-interstitials I3) can be due to another I3 local defect environment which, in turn, depends on the irradiation conditions. The SiO2 film changes the shape of the distribution of primary defects, thereby assisting the separation of interstitials from vacancies. This reduces the concentration of vacancy complexes in the environment of I3, thereby shifting the spectral position of PL line and changing their properties. Such explanation is supported by the study of damage using transmission electron microscopy and by measuring PL spectra before and after removal of top silicon layers. A correlation between the PL intensity and the degree of structural damage at different depths is established. The important role of oxygen impurity, the concentration of which near the SiO2/Si interface increases due to the penetration of recoil atoms into silicon, is noted. The obtained results open up the way to create the relatively thermo-stable light-emitting complexes of point defects for silicon-based optoelectronics and quantum photonics.

Optoelectronic integrated circuits for analog optical computing: Development and challenge

Over the past 2 decades, researches in artificial neural networks (ANNs) and deep learning have flourished and enabled the applications of artificial intelligence (AI) in image recognition, natural language processing, medical image analysis, molecular and material science, autopilot and so on. As the application scenarios for AI become more complex, massive perceptual data need to be processed in real-time. Thus, the traditional electronic integrated chips for executing the calculation of ANNs and deep learning algorithms are faced with higher requirements for computation speed and energy consumption. However, due to the unsustainability of Moore’s Law and the failure of the Dennard’s scaling rules, the growth of computing power of the traditional electronic integrated chips based on electronic transistors and von Neumann architecture could difficultly match the rapid growth of data volume. Enabled by silicon-based optoelectronics, analog optical computing can support sub-nanosecond delay and ∼fJ energy consumption efficiency, and provide an alternative method to further greatly improve computing resources and to accelerate deep learning tasks. In Chapter 1, the challenges of electronic computing technologies are briefly explained, and potential solutions including analog optical computing are introduced. Then, separated by four photonic platforms, including coherent integration platform, incoherent integration platform, space-propagation optical platform, and optical fiber platform, the recent important research progresses in analog optical computing are outlined in Chapter 2. Then, the nonlinearity and training algorithm for analog optical computing are summarized and discussed in Chapter 3. In Chapter 4, the prospects and challenges of analog optical computing are pointed out.

Effect of H2 for Growing Germanium–Lead Alloys By Magnetron Sputtering Epitaxy

Si and Ge are indirect bandgap materials, and their low light emission efficiency limits the development of silicon-based optoelectronics. Studies have shown that the introduction of Pb into Ge can make the Γ valley decrease faster than the L valley, and GePb alloys can be transformed into direct bandgap materials, thereby realizing high-efficiency luminescence of silicon-based materials. Since Pb atoms have a larger core and can provide a greater electronegativity difference for Ge, GePb alloys can be transformed into direct bandgap materials with only about 3.4% Pb. In addition, the maximum optical gain of GePb alloys is much higher than that of GeSn alloys, as revealed by first principal calculations. Therefore, the epitaxial investigation of GePb alloys is of great significance for Si photonics. In this work, Ge1- x Pb x (1.2% < x < 2.4%) alloys were grown by magnetron sputtering epitaxy using H2 and Ar mixture. The effects of different proportions of H2 and Ar on the growth of GePb were studied in detail. High crystal quality Ge0.984Pb0.016 alloys without Pb surface segregation were successfully fabricated. The results show that the increase of H2/Ar ratio contributes to the increase of Pb composition in GePb alloys. Figure 1

(Digital Presentation) Fabrication of Microbridges Based on Ge-on-SOI and Observation of Strong Resonant Light Emission

Introduction Ge is one of the most attractive material for silicon-based optoelectronics because it can be epitaxially grown on a Si substrate, allowing us to integrate Ge based light emitters and photodetectors monolithically on the Si platform. Although Ge is an indirect band gap semiconductor like Si, by epitaxially growing Ge on the Si substrate, tensile strain is introduced into Ge, resultantly leading to the Γ-valley shifts and increase in the light emission efficiency via the direct transition. The amount of the strain induced in Ge-on-Si, however, is not sufficiently large, demanding other methods of applying large tensile strain to Ge. Fabrication of Ge microbridge structure is expected to induce the larger strain and further improve light emission efficiency [1]. In general, microbridges reported so far have been fabricated by the electron beam lithography process, which is not appropriate for mass production. In this study, we fabricate Ge microbridge by simple photolithography process based on Ge-on-Si and Ge-on-SOI structures and very strong room temperature photoluminescence is obtained and strong resonant peaks can be observed. Experimental Method Ge layers were grown on a Si (110) wafer (Ge-on-Si) or a SOI (100) wafer (Ge-on-SOI) using a two-step growth method by solid source MBE. Firstly, a 40nm thick buffer layer at a low temperature of 350 ~ 400℃. Secondly, a 500 nm thick Ge layer was grown at a high temperature of 550 ~ 650℃. Post-growth-annealing was carried out at 800℃ for 10 minutes. The microbridge structures were defined by the standard photolithography process and mesa etching was performed by the reactive ion etching. Subsequently, the Si under the bridge and pads was selectively removed by KOH etchant, leading to free-standing Ge microbridge. For the Ge-on-SOI, the underlying SiO2 layer (buried oxide) was additionally removed by HF. Results and Discussion It was observed by SEM measurements that the Ge microbridges fabricated from Ge-on-Si were slightly warped from both ends to the center of the bridges. Hydrogen gases generated due to the reaction of Si and KOH during the selective etching are considered to be responsible for the warping of the microbridges, which makes it difficult to control the strain of the Ge. The selective etching time, therefore, has to be minimized to reduce the effects of the gas generation. For this purpose, the microbridges were fabricated from Ge-on-SOI, where the floating structure can be easily formed by the etching of the buried SiO2 layer with HF and the etching time of Si with KOH was reduced by a factor of four. As a result, the warping was completely suppressed and very flat microbridges were fabricated without any warping.Photoluminescence measurements at the center of the microbridge on Ge-on-SOI were performed at room temperature. Strong PL emissions were obtained in the wavelength range of 1630-2000 nm, where several strong resonant peaks appear. This resonance is considered to occur due to reflection at the side wall of the bridge and the peaks can be well fitted with the cavity length of the bridge width. Also, we carried out PL measurements from one end to another end of the bridge, and investigated the bridge position dependence of the PL emission. It was found that the light emission intensity increased toward the center of the bridge, and the highest intensity was obtained at the center. Moreover, the strain amounts were measured by micro Raman line scan along the bridge and strain dependence of PL emission was investigated. It was also shown that the strain amount increased toward the center of the bridge and became the highest at it. It was demonstrated that the higher PL intensity can be obtained due to the higher tensile strain at the center of the microbridge. In summary, we fabricated Ge microbridge structures by photolithography process and obtained strong room temperature resonant light emission from the Ge microbridges formed from Ge-on-SOI where bridge-warping was completely suppressed by shortening the etching time. From this result, we can say that the Ge microbridge light emitting devices are very promising for applications to the light sources on the Si platform.This work was partially supported by JSPS KAKENHI (Nos. 19H02175, 19H05616 and 20K21009).[1] M. J. Suess et al, Nat. Photonics 7: 466, 2013 Figure 1

Silicon-based optoelectronics for general-purpose matrix computation: a review

Conventional electronic processors, which are the mainstream and almost invincible hardware for computation, are approaching their limits in both computational power and energy efficiency, especially in large-scale matrix computation. By combining electronic, photonic, and optoelectronic devices and circuits together, silicon-based optoelectronic matrix computation has been demonstrating great capabilities and feasibilities. Matrix computation is one of the few general-purpose computations that have the potential to exceed the computation performance of digital logic circuits in energy efficiency, computational power, and latency. Moreover, electronic processors also suffer from the tremendous energy consumption of the digital transceiver circuits during high-capacity data interconnections. We review the recent progress in photonic matrix computation, including matrix-vector multiplication, convolution, and multiply–accumulate operations in artificial neural networks, quantum information processing, combinatorial optimization, and compressed sensing, with particular attention paid to energy consumption. We also summarize the advantages of silicon-based optoelectronic matrix computation in data interconnections and photonic-electronic integration over conventional optical computing processors. Looking toward the future of silicon-based optoelectronic matrix computations, we believe that silicon-based optoelectronics is a promising and comprehensive platform for disruptively improving general-purpose matrix computation performance in the post-Moore’s law era.

Erbium chloride silicate-based vertical cavity surface-emitting laser at the near-infrared communication band.

Silicon-based integrated optoelectronics has become a hotspot in the field of computers and information processing systems. An integrated coherent light source on-chip with a small footprint and high efficiency is one of the most important unresolved devices. Here, we realize a silicon-based vertical cavity surface-emitting laser in the near-infrared communication band by making efforts in both controlled preparation of high-gain erbium silicate materials and novel design of high optical feedback microcavity. Single-crystal erbium/ytterbium silicate microplates with erbium concentration as high as 5 × 1021 cm-3 are controlled prepared by a chemical vapor deposition method. They can produce strong luminescence with quite a long lifetime (2.3 ms) at the wavelength of 1.5 μm. By embedding the erbium silicate microplates between two dielectric Bragg reflectors, we construct a vertical cavity surface-emitting laser at 1.5 μm, with a lasing threshold as low as 20 μJ/cm2 and Q factor of nearly 2000. Our study provides a new pathway to achieve a sub-micrometer coherent light source for optical communication.

Experimental research on ultracompact silicon hybrid plasmonic nanofocusing device

Silicon-based optoelectronics, using the mature silicon-based microelectronic complementary metal oxide semiconductor (CMOS) manufacturing process, is a large-scale optoelectronic integration platform that has attracted much attention. Surface plasmonic devices have also received extensive attention in the past decades, and especially the silicon-based surface plasmonic nanofocusing devices have become a research hotspot. Typical nanofocusing structures include chirped surface gratings, plasmonic Fresnel zone plate, nano-slit array, tapered metal tips. However, there occur some inevitable problems in these devices, such as the fine structure being too complex to be fabricated and too large transmission loss of metal slot waveguide. In this work, an ultra-compact hybrid surface plasmon nanofocusing device is designed and fabricated by the silicon-based optoelectronic technology, and the nanofocusing performance of the device is also experimentally verified. The hybrid surface plasmon nanofocusing devices are fabricated on a silicon-on-insulator (SOI) wafer by electron beam lithography (EBL) system. The silicon wire waveguides, tapers and the thin silicon strips in the middle of nanofocusing regions are patterned in only one step EBL. The gold layer is formed by a deposition and lift-off process, and then a partially etching process is introduced to make the thickness of the middle thin silicon strips the same as that of the gold layer. With a 1.23-μm-long tapered structure, our nanofocusing devices focus the light field of a silicon strip waveguide into a hybrid surface plasmon waveguide, making non-resonant optical field increase 20 times in the 1550 nm near-infrared band experimentally. The entire insertion loss is about 4.6 dB, and the mode area of the nanofocusing area is about &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}${\left( {\lambda /n} \right)^2}/640$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20212340_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20212340_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; which is over 300 times smaller than that of the input silicon waveguide. When the middle slot silicon waveguide width &lt;i&gt;W&lt;/i&gt;&lt;sub&gt;Si&lt;/sub&gt; = 120 nm, the insertion loss reaches a minimum value of 2.8 dB. In our design, we adopt the design of silicon-based hybrid plasmonic waveguides. In this design, a layer of material with low refractive index is inserted between the metal layer and the silicon layer to act as a “container” of light field, which makes this silicon-based hybrid plasmonic waveguides have less loss than the traditional metal plasmonic waveguides, and can still maintain high optical field localization. Such silicon-based hybrid surface plasmon nanofocusing devices with simple structures and excellent performances are promising alternatives for future applications in optical field manipulation, optical sensing, nonlinear optical devices, and optical phase-change storage.

Angle-Resolved Intensity of In-Axis/Off-Axis Polarized Micro-Raman Spectroscopy for Monocrystalline Silicon

Monocrystalline silicon (c-Si) is still an important material related to microelectronics/optoelectronics. The nondestructive measurement of the c-Si material and its microstructure is commonly required in scientific research and industrial applications, for which Raman spectroscopy is an indispensable method. However, Raman measurements based on the specific fixed Raman geometry/polarization configuration are limited for the quantified analysis of c-Si performance, which makes it difficult to meet the high-end requirements of advanced silicon-based microelectronics and optoelectronics. Angle-resolved Raman measurements have become a new trend of experimental analysis in the field of materials, physics, mechanics, and optics. In this paper, the characteristics of the angle-resolved polarized Raman scattering of c-Si under the in-axis and off-axis configurations are systematically analyzed. A general theoretical model of the angle-resolved Raman intensity is established, which includes several alterable angle parameters, including the inclination angle, rotation angle of the sample, and polarization directions of the incident laser and scattered light. The diversification of the Raman intensity is given at different angles for various geometries and polarization configurations. The theoretical model is verified and calibrated by typical experiments. In addition, this work provides a reliable basis for the analysis of complex polarized Raman experiments on silicon-based structures.

Evolution of laser-induced strain in a Ge crystal for the [111] and [100] directions probed by time-resolved X-ray diffraction

Ultra-short laser-pulse-induced strain propagation in a Ge crystal is studied in the [111] and [100] directions using time-resolved X-ray diffraction (TXRD). The strain propagation velocity is derived by analysis of the TXRD signal from the strained crystal planes. Numerical integration of the Takagi–Taupin equations is performed using open source code, which provides a very simple approach to estimate the strain propagation velocity. The present method will be particularly useful for relatively broad spectral bandwidths and weak X-ray sources, where temporal oscillations in the diffracted X-ray intensity at the relevant phonon frequencies would not be visible. The two Bragg reflections of the Ge sample, viz. 111 and 400, give information on the propagation of strain for two different depths, as the X-ray extinction depths are different for these two reflections. The strain induced by femtosecond laser excitation has a propagation velocity comparable to the longitudinal acoustic velocity. The strain propagation velocity increases with increasing laser excitation fluence. This fluence dependence of the strain propagation velocity can be attributed to crystal heating by ambipolar carrier diffusion. Ge is a promising candidate for silicon-based optoelectronics, and this study will enhance the understanding of heat transport by carrier diffusion in Ge induced by ultra-fast laser pulses, which will assist in the design of optoelectronic devices.

Silicon-Based Optoelectronics Enhanced by Hybrid Plasmon Polaritons: Bridging Dielectric Photonics and Nanoplasmonics

Silicon-based optoelectronics large-scale integrated circuits have been of interest to the world in recent decades due to the need for higher complexity, larger link capacity, and lower cost. Surface plasmons are electromagnetic waves that propagate along the interface between a conductor and a dielectric, which can be confined several orders smaller than the wavelength in a vacuum and offers the potential for minimizing photonic circuits to the nanoscale. However, plasmonic waveguides are usually accompanied by substantial propagation loss because metals always exhibit significant resistive heating losses when interacting with light. Therefore, it is better to couple silicon-based optoelectronics and plasmonics and bridge the gap between micro-photonics and nanodevices, especially some nano-electronic devices. In this review, we discuss methods to enhance silicon-based optoelectronics by hybrid plasmon polaritons and summarize some recently reported designs. It is believed that by utilizing the strong light confinement of plasmonics, we can overcome the conventional diffraction limit of light and further improve the integration of optoelectronic circuits.

(Invited) Silicon Nanosheets as Candidates for Silicon-Based Optoelectronics

Colloidal Group IV nanomaterials (Si, Ge, Sn and their alloys) are of great interest due to their potential to offer broadly tunable optical properties. By manipulating composition, size, or surface chemistry Group IV nanomaterials have potential to serve as nontoxic, earth abundant phosphors or semiconductors that can be used for optoelectronic applications that span the ultraviolet to the mid-infrared spectral ranges. The synthesis of colloidal Group IV nanostructures is challenging due to the highly covalent character of Si and Ge, and typically require temperatures in excess of 400°C to form crystalline particles. We have recently reported new synthetic methods for Si and Ge nanomaterials derived from precursors synthesized in the solid-state, including suboxides and Zintl phases. In each of these cases, colloidal nanostructures can be accessed by selectively removing unwanted components from the solid-state precursor, liberating nanostructures that are terminated with atomic or molecular species such as hydrogen atoms or methyl groups. We also characterize the structural properties of the Group IV nanostructures that we synthesized using a combination of infrared spectroscopy, solid-state NMR, and pair distribution function analysis to confirm the structure and order. In the case of Si and Ge, single-atom thick nanosheets were synthesized, their stability and decomposition at elevated temperatures were characterized. The optical properties of Group IV nanomaterials have sparked debate over the past few decades. We found that Si nanosheets exhibit fast (nanosecond) photoluminescence lifetime, which is several orders of magnitude greater than Si nanocrystals, and offer potential explanations for the observed difference. Finally we show that Si and Ge nanocrystals and nanosheets can be used for sensing applications, including infrared photodetectors and ionophore-based sensing schemes.

Cr cation-anchored carbon nanosheets: synthesis, paramagnetism and ferromagnetism

Since the successfully synthesis of monolayer graphene, carbon-based materials have attracted wide and extensive attentions from researches. Due to the excellent transport capacity and conductivity, they are promising to be applied in electronic devices, even substituting the silicon-based electronic devices, optoelectronics and spintronics. Nevertheless, due to the non magnetic feature, many efforts have been devoted to endow carbon materials magnetism to apply them in the spintronic devices fabrication. Herein, a strategy of Cr cation solely anchored on two-dimensional carbon nanosheets by Cr–N bonds is developed, which introduces magnetism in carbon nanosheets. By extended x-ray absorption fine structure characterization, Cr cations are demonstrated to be atomically dispersed with Cr–N3 coordination. And after Cr–N3 anchored, carbon nanosheets exhibit ferromagnetic features with paramagnetic background. The magnetization varies with Cr content and reaches the maximum (Cr: 2.0%, 0.86 emu g−1) under 3 T at 50 K. The x-ray magnetic circular dichroism and first-principle calculations indicate that the magnetism is caused by the Cr3+ component of the anchored Cr cations. This study sets a single cation anchoring carbon as a suitable candidate for future spintronics.

(Invited) Silicon Nanosheets as Candidates for Silicon-Based Optoelectronics

The growth in computational ability over the past decades has positively impacted global development, the economy, healthcare, and science. As on-chip components are approaching the atomic scale, alternative paradigms are needed to address the thermal and electronic issues that impose bottlenecks for computing. One approach to address this is with optoelectronics. However, silicon—the backbone of microelectronics—is a poor choice due to its indirect bandgap, while existing optoelectronic materials are incompatible with CMOS infrastructure. Monolayer silicon nanosheets (SiNSs) are an intriguing material that exhibit photoluminescence, and are compositionally-compatible with the CMOS process. Here, we synthesize and characterize monolayer SiNSs, and show spectroscopic evidence that they exhibit a quasi-direct bandgap, which is corroborated by DFT calculations. We probe their thermal stability, demonstrating their structure and photoluminescence are stable beyond the required operating temperatures for computing applications. These optoelectronic properties, CMOS-compatibility, and stability make SiNSs a viable candidate for silicon-based photonics.

High-speed electroluminescence from semiconducting carbon nanotube films

High-speed light emitters integrated on silicon chips can enable novel architectures for silicon-based optoelectronics, such as on-chip optical interconnects and silicon photonics. However, conventional light sources based on compound semiconductors face major challenges for their integration with the silicon-based platforms because of the difficulty of their direct growth on a silicon substrate. Here, we report high-speed, ultra-small-size on-chip electroluminescence (EL) emitters based on semiconducting single-walled carbon nanotube (SWNT) thin films. The peaks of the EL emission spectra are about 0.15-eV redshifted from the peaks of the absorption and photoluminescence emission spectra, which probably suggest emission from trions. High-speed responses of ∼100 ps were experimentally observed from the EL emitters, which indicate the possibility of several-GHz modulation. The pulsed light generation was also obtained by applying the pulse voltage. These high-speed and ultra-small-size EL emitters can enable novel on-chip optoelectronic devices for highly integrated optoelectronics and silicon photonics.

Temperature dependence of dislocation-related photoluminescence (D1) of self-implanted silicon subjected to additional boron implantation

The goal of this work is the qualitative and quantitative interpretation of experimental data obtained for the effect of additional boron ion implantation on the temperature dependence of dislocation-related luminescence (D1 line) of self-implanted silicon. This goal is motivated by the need in development of effective light emitter for silicon-based optoelectronics. The model explaining the previously established improvement of the D1 line temperature dependence is suggested and supported by computer calculations based on a set of kinetic equations taking into account the radiative and nonradiative electron transitions between energy levels.

Control of interaction between Tm2O3 layers in electroluminescent Al2O3/ Tm2O3 nanolaminate films fabricated by atomic layer deposition

The interaction between single Tm2O3 layers in electroluminescent Al2O3/Tm2O3 nanolaminate films fabricated by atomic layer deposition, is investigated through the adjustment of the Al2O3 spacer layer thickness and annealing temperature. The EL intensities and decay time from different energy levels of the Tm3+ ions in Al2O3/Tm2O3 nanolaminates are explored, all of which derive a ∼1.5 nm Förster distance, manifesting a critical distance of ∼3 nm to eliminate the non-radiative interaction between adjacent Tm2O3 layers, which quenches the excited electrons to the ground energy level rather than relax to lower excited states. The diffusion of Tm3+ ions and resulting cluster formation under high temperature annealing also influence the abovementioned interaction, and 800 °C is suitable to minimize the diffusion while activate Tm3+ emissions. This work provides the basis for the exploitation of rare earth-doped nanolaminates in optical communication and silicon-based optoelectronics.

The particulars properties of annealing temperature and spacer thickness on cross-relaxation and decay dynamics in Aluminum Oxide upon Thulium(III) oxide nanolaminate silicon-based electroluminescent and optoelectronics devices

The effects of thermal treatment and Aluminum Oxide [Al2O3] spacer thickness on the de-excitation traces and cross-relaxation among Thulium(III) ions [Tm3+], which prominently impact on the electroluminescence (EL) from different characteristic transitions inside the devices based on Aluminum Oxide upon Thulium(III) Oxide [[Al2O3]/[Tm2O3]] nanolaminate thin solid films, were investigated. The suitable annealing temperatures (Ta) for activating [Tm3+] ions was between 600.0 °C and 800.0 °C, while higher annealing temperatures lead to the reduced EL intensity and life time, resulting from the formation of Thulium Oxide nonstoichiometric compound [TmOx] clusters or agglomerations. All phenomena confirm the critical [Al2O3] spacer thickness of around 3.0 nm, concerning both non-radioactive interaction among excited [Tm3+] ions derived from Förster mode and the acceleration distance for the injected electrons in [Al2O3] matrix.

Improving CNT-Si solar cells by metal chloride-to-oxide transformation

Transitional metal oxides (TMOs) are important functional materials in silicon-based and thin-film optoelectronics. Here, TMOs are applied in carbon nanotube (CNT)-Si solar cells by spin-coating solutions of metal chlorides that undergo favorable transformation in ambient conditions. An unconventional change in solar cell behavior is observed after coating two particular chlorides (MoCl5 and WCl6, respectively), characterized by an initial severe degradation followed by gradual recovery and then well surpassing the original performance. Detailed analysis reveals that the formation of corresponding oxides (MoO3 and WO3) enables two primary functions on both CNTs (p-type doping) and Si (inducing inversion layer), leading to significant improvement in open-circuit voltage and fill factor, with power conversion efficiencies up to 13.0% (MoO3) and 13.4% (WO3). Further combining with other chlorides to increase the short-circuit current, ultimate cells efficiencies achieve >16% with over 90% retention after 24 h, which are among the highest stable efficiencies reported for CNT-Si solar cells. The transformation of functional layers as demonstrated here has profound influence on the device characteristics, and represents a potential strategy in low-cost manufacturing of next-generation high efficiency photovoltaics.