Silicon Photonics Applications Research Articles

(Dielectric Science & Technology Thomas Callinan Award) Rare-Earth Luminescence in Silicon-Based Thin Film Structures

For Si-based materials to be used in solid-state lighting and silicon photonics schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished using rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. In this talk, we first will provide a review of our work in this field and then focus on Eu-doped films, which are particularly attractive for silicon photonic applications due to their intense emission in the visible spectral region [1]. We will also discuss the benefits of introducing a novel hybrid radio frequency (RF) magnetron sputtering source in the electron cyclotron resonance (ECR) plasma enhanced chemical vapour deposition (PECVD) reactor chamber [2], using the example of Tb-doped SiON films [3]. This approach contrasts with traditional doping methods which use metal-organic precursors or ion implantation to introduce rare-earth dopant species into the host matrix.[1] F. Azmi et al., “Tunable Emission from Eu:SiOxNy Thin Films Prepared by Integrated Magnetron Sputtering and Plasma Enhanced Chemical Vapor Deposition”, J. Vac. Sci. Technol. A 40, 043402 (2022); DOI: 10.1116/6.0001761[2] J.W. Miller et al., “Integrated ECR-PECVD and Magnetron Sputtering System for Rare-Earth-Doped Si-Based Materials”, Surface and Coatings Technology 336, 99 (2018); DOI: 10.1016/j.surfcoat.2017.08.051[3] Z. Khatami et al., "A comprehensive calibration of integrated magnetron sputtering and plasma enhanced chemical vapor deposition for rare-earth doped thin films", J. Mater. Res. (2023); DOI: 10.1557/s43578-023-01207-2

Design and experimental demonstration of a high-performance all-silicon transverse magnetic polarizer using tilted-elliptical-hole arrays

This study presents the design and experimental demonstration of a high-performance all-silicon transverse magnetic (TM) polarizer. The tilted-elliptical-hole arrays are designed to effectively reflect transverse electric (TE) modes while propagating TM modes with low loss. The device bandwidth (BW) is controlled by changing the tilting angle of the elliptical hole or by combining it with changes in other parameters. The device operates beyond 326 nm (1385–1711 nm) in BW, achieving an average insertion loss (IL) below 1.0 dB and a polarization extinction ratio (PER) over 20 dB. A 20 nm shift in BW can be obtained with a 30° deflection, and an 80 nm shift can be achieved with multiple parameter changes. The experimental results confirm the theoretical analysis. The present device with the advantages of simple structure, flexible design, and broad BW has great potential applications in silicon photonics.

Ultrafast Laser Hyperdoped Black Silicon and Its Application in Photodetectors: A Review

Based on the ultrafast and extremely strong interaction between laser pulses and materials, ultrafast laser irradiation can break the solid solubility constraints and enable hyperdoping of impurities. This process overcomes the bandgap constraints of crystalline silicon, resulting in heightened absorption across a broad spectral range spanning from ultraviolet to infrared wavelengths, therefore commonly referred to as black silicon (b‐Si). The b‐Si demonstrates significant changes in optoelectronic properties, making it highly promising for applications in silicon photonics. Specifically, b‐Si photodetectors exhibit distinct advantages in terms of high photoelectric gain at low voltage, ultrabroadband spectral responsivity, large dynamic range, and suitability for operation over a wide temperature range. These properties address the limitations of traditional silicon photodetectors, showcasing great potential for applications in optoelectronic integration, artificial intelligence, information technology, energy devices, and beyond. This review focuses on b‐Si achieved through ultrafast laser processing, with a special emphasis on its applications in photodetectors. The mechanism of ultrafast laser irradiation and the properties of hyperdoped silicon are discussed. Then, the research progresses and state‐of‐the‐art b‐Si photodetectors are introduced, as well as working mechanism and potential application expansion. Finally, the development prospects of b‐Si photodetectors based on ultrafast laser hyperdoping are predicted.

Optical and Mechanical Properties of Si-Based Thin Films for Photonic Applications

In this talk, we will review recent advances in the fabrication and characterization of silicon-based thin film structures for photonic applications, including rare earth doped silicon oxynitrides and luminescent silicon carbonitrides.For Si-based materials to be used in solid-state lighting (SSL) and silicon photonics schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished using rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. After a brief review of the latest developments in the field, this talk will focus on Eu-doped films, which are attractive for silicon photonic applications due to their intense emission in the visible spectral region [1]. The films are fabricated by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) and doping is accomplished using a novel hybrid radio frequency (RF) magnetron sputtering source in the ECR-PECVD reactor chamber [2]. This approach contrasts with traditional doping methods which use metal-organic precursors to introduce rare-earth dopant species into the host matrix. We will discuss the relationship between the photoluminescence, elasticity, and hardness of Eu doped silicon oxynitride (SiON) thin films.As the efficiency of photonic devices can be influenced by the mechanical properties of the deposited films, a good understanding of their mechanical properties is required for the integration of these films in photonic devices. SiNx thin films, for example, play an important role in strain engineering of active photonic devices, such as diode lasers fabricated on GaAs or InP substrates. We will discuss results of a collaboration between McMaster and the Université de Rennes in France, aimed at quantifying the effects of structured dielectric thin films on the generation of a mechanical strain field in the semiconductor through tuning the amount of mechanical stress present in the dielectric thin film, as a function of the details of the deposition process [3].[1] Fahmida Azmi et al., “Tunable Emission from Eu:SiOxNy Thin Films Prepared by Integrated Magnetron Sputtering and Plasma Enhanced Chemical Vapor Deposition”, J. Vac. Sci. Technol. A 40, 043402 (2022); https://doi.org/10.1116/6.0001761[2] J.W. Miller et al., “Integrated ECR-PECVD and Magnetron Sputtering System for Rare-Earth-Doped Si-Based Materials”, Surface and Coatings Technology 336, 99 (2018); doi: 10.1016/j.surfcoat.2017.08.051[3] Brahim Ahammou et al., “Strain engineering in III-V photonic components through structuration of SiNx films”, J. Vac. Sci. Technol. B 40, 012202 (2022); doi: 10.1116/6.0001352

Electronic band structures and spin-charge densities of edge-functionalized silicene nanoribbons as promising candidates for either optoelectronics or spintronics applications

Two-dimensional nanomaterials including graphene as well as its nanoribbons have started to occur, which has accelerated the growth of contemporary nanotechnology. Silicene, a silicon equivalent of graphene, has the main advantage that it can be employed in present silicon nanostructure-based production processes. Using density functional theory within the generalized gradient approximation, we offer the structural, electronic, and magnetic properties of edge-functionalized silicene nanoribbons (nX-zSiNR-mX’)(where, X/X’ = F, Cl or H; n, m = 1 or 2) in magnetic-order NM, FM, and AFM, respectively. Two modes homogeneous and heterogeneous asymmetric are accomplished. The spin density is mainly localized on halogen and Si atoms. Thus, future spin-dynamics processes for spintronics applications could be accomplished on these systems. Our computed outcomes reveal that the pristine nanoribbon 8-SiNR is a metal material once the NM and FM magnetic orders are involved, whereas it is a semiconductor with a small band gap energy when the AFM magnetic order is employed. Moreover, we find that the zigzag nX-zSiNR-mX’ compounds are metals in either case homogeneous or even heterogeneous. Nevertheless, a band gap energy up a limit to 520 meV (2H-zSiNR-1H) can be achieved under an external electric field with a strength of 4.0 V/Å. We carefully investigate the effect of the edge-functionalized silicene nanoribbon width on their spin density distribution and electronic band structures. Further, the effect of nanoribbon width on the edge formation energy and magnetic moment is systematically studied. Our outcomes reveal the potential of these nanoribbons as advantageous candidates for silicon photonic, optoelectronic devices, and spintronics applications.

Ultra‐Low Loss SiN Edge Coupler for III‐V/SiN Hybrid Integration

AbstractSilicon photonics is becoming a competitive technology to settle the issues of power and speed in data centers and computing systems. However, the absence of an on‐chip light source restricts the wide and deep application of silicon photonics. Essentially, efficient edge coupling from a Si‐based III‐V laser to silicon photonic components remains the major obstacle for on‐chip integration. Here, two compact edge couplers with ultra‐low coupling loss and eased fabrication for the light transmission from a Si‐based III‐V laser to Si3N4 waveguide are realized. An ultra‐low laser‐to‐chip coupling loss of only 1.175 dB for the butt coupling of a Si‐based InAs QD laser is experimentally demonstrated with high alignment tolerance. The strategies presented here provide a competitive solution for realizing ultra‐efficient integration of Si‐based light sources and silicon photonic components.

Ultra-compact and ultra-broadband arbitrary-order silicon photonic multi-mode converter designed by an intelligent algorithm.

Multi-mode converters, which can achieve spatial mode conversion in multimode waveguide, play a key role in multi-mode photonics and mode-division multiplexing (MDM). However, rapid design of high-performance mode converters with ultra-compact footprint and ultra-broadband operation bandwidth is still a challenge. In this work, through combining adaptive genetic algorithm (AGA) and finite element simulations, we present an intelligent inverse design algorithm and successfully designed a set of arbitrary-order mode converters with low excess losses (ELs) and low crosstalk (CT). At the communication wavelength of 1550 nm, the footprint of designed TE0-n (n = 1, 2, 3, 4) and TE2-n (n = 0, 1, 3, 4) mode converters are only 1.8 × 2.2 µm2. The maximum and minimum conversion efficiency (CE) is 94.5% and 64.2%, and the maximum and minimum ELs/CT are 1.92/-10.9 dB and 0.24/-20 dB, respectively. Theoretically, the smallest bandwidth for simultaneously achieving ELs ≤ 3 dB and CT ≤ -10 dB exceeds 70 nm, which can be as large as 400 nm for the case of low-order mode conversion. Moreover, the mode converter in conjunction with a waveguide bend allows for mode-conversion in ultra-sharp waveguide bends, significantly increasing the density of on-chip photonic integration. This work provides a general platform for the realization of mode converters and has good prospect in application of multimode silicon photonics and MDM.

СТРАТЕГІЇ ТЕХНОЛОГІЧНОГО РОЗВИТКУ АПАРАТНОГО ЗАБЕЗПЕЧЕННЯ ІНФОКОМУНІКАЦІЙНИХ РАДІОМЕРЕЖ

Technologies for building telecommunication systems and networks based on 6G technology, which will be able to provide access to new functionality and information services using innovative wireless technologies and artificial intelligence methods, are considered. At the same time, information communication systems based on 6G are characterized by new functional parameters and devices, in particular, a new spectrum, new channels, new materials, new antennas, new computing technologies and new end devices, taking into account the possibility of simultaneous use of the THz range for communication and the scanning process. The operation of communication and scanning systems in new high-frequency ranges based on new materials and antennas is based on the application of silicon photonics, photonic crystals, heterogeneous, reconfigurable, photoelectric and plasmonic materials. At the same time, there is also a need to use new types of antennas for the THz frequency ranges. This is especially important, because due to significant transmission losses in the THz range, antennas are significantly different from conventional antennas that are connected to radio frequency systems via coaxial cables or microstrip lines. Given that Moore's law will soon lose its relevance, research into new computing technologies, such as computing based on artificial intelligence structures and quantum computing, has begun. The key indicators of the effectiveness of future telecommunication terminal devices as part of 6G information communication radio networks are considered and their functional capabilities are determined. The study of the architecture of terahertz communication systems was carried out using two different approaches to the construction of hardware: electronic, where radio frequencies are multiplied up to THz; and photonic, where optical frequencies are divided up to THz. It has been determined that most of such systems and networks are used for communication over short distances inside premises due to high atmospheric attenuation in the THz range. The prerequisites for achieving higher characteristics due to the addition of new materials to the silicon chip, such as photonic crystals, photovoltaic elements and plasma surfaces, are considered. As a result, new on-chip and in-body antenna designs, along with compact lens technology such as RIS, can provide more accurate implementation of the desired antenna characteristics, as well as reduce system size. Opportunities to use new communication and visualization methods have been identified, but implementation of terahertz systems based on electronics, optoelectronics, and photonics will depend on the usage scenario and operating frequencies.

Two-dimensional optoelectronic devices for silicon photonic integration

With the unprecedented increasing demand for extremely fast processing speed and huge data capacity, traditional silicon-based information technology is becoming saturated due to the encountered bottlenecks of Moore's Law. New material systems and new device architectures are considered promising strategies for this challenge. Two-dimensional (2D) materials are layered materials and garnered persistent attention in recent years owing to their advantages in ultrathin body, strong light-matter interaction, flexible integration, and ultrabroad operation wavelength range. To this end, the integration of 2D materials into silicon-based platforms opens a new path for silicon photonic integration. In this work, a comprehensive review is given of the recent signs of progress related to 2D material integrated optoelectronic devices and their potential applications in silicon photonics. Firstly, the basic optical properties of 2D materials and heterostructures are summarized in the first part. Then, the state-of-the-art three typical 2D optoelectronic devices for silicon photonic applications are reviewed in detail. Finally, the perspective and challenges for the aim of 3D monolithic heterogeneous integration of these 2D optoelectronic devices are discussed.

Wafer-Scale Growth of Sb2Te3 Films via Low-Temperature Atomic Layer Deposition for Self-Powered Photodetectors.

In this work, we demonstrate the performance of a silicon-compatible, high-performance, and self-powered photodetector. A wide detection range from visible (405 nm) to near-infrared (1550 nm) light was enabled by the vertical p-n heterojunction between the p-type antimony telluride (Sb2Te3) thin film and the n-type silicon (Si) substrates. A Sb2Te3 film with a good crystal quality, low density of extended defects, proper stoichiometry, p-type nature, and excellent uniformity across a 4 in. wafer was achieved by atomic layer deposition at 80 °C using (Et3Si)2Te and SbCl3 as precursors. The processed photodetectors have a low dark current (∼20 pA), a high responsivity of (∼4.3 A/W at 405 nm and ∼150 mA/W at 1550 nm), a peak detectivity of ∼1.65 × 1014 Jones, and a quick rise time of ∼98 μs under zero bias voltage. Density functional theory calculations reveal a narrow, near-direct, type-II band gap at the heterointerface that supports a strong built-in electric field leading to efficient separation of the photogenerated carriers. The devices have long-term air stability and efficient switching behavior even at elevated temperatures. These high-performance and self-powered p-Sb2Te3/n-Si heterojunction photodetectors have immense potential to become reliable technological building blocks for a plethora of innovative applications in next-generation optoelectronics, silicon-photonics, chip-level sensing, and detection.

Integrated metasurfaces on silicon photonics for emission shaping and holographic projection

Abstract The emerging applications of silicon photonics in free space, such as LiDARs, free-space optical communications, and quantum photonics, urge versatile emission shaping beyond the capabilities of conventional grating couplers. In these applications, silicon photonic chips deliver free-space emission to detect or manipulate external objects. Light needs to emit from a silicon photonic chip to the free space with specific spatial modes, which produce focusing, collimation, orbital angular momentum, or even holographic projection. A platform that offers versatile shaping of free-space emission, while maintaining the CMOS compatibility and monolithic integration of silicon photonics is in pressing need. Here we demonstrate a platform that integrates metasurfaces monolithically on silicon photonic integrated circuits. The metasurfaces consist of amorphous silicon nanopillars evanescently coupled to silicon waveguides. We demonstrate experimentally diffraction-limited beam focusing with a Strehl ratio of 0.82. The focused spot can be switched between two positions by controlling the excitation direction. We also realize a meta-hologram experimentally that projects an image above the silicon photonic chip. This platform can add a highly versatile interface to the existing silicon photonic ecosystems for precise delivery of free-space emission.

Roughness Suppression in Electrochemical Nanoimprinting of Si for Applications in Silicon Photonics

Metal-assisted electrochemical nanoimprinting (Mac-Imprint) scales the fabrication of micro- and nanoscale 3D freeform geometries in silicon and holds the promise to enable novel chip-scale optics operating at the near-infrared spectrum. However, Mac-Imprint of silicon concomitantly generates mesoscale roughness (e.g., protrusion size≈45nm) creating prohibitive levels of light scattering. This arises from the requirement to coat stamps with nanoporous gold catalyst that, while sustaining etchant diffusion, imprints its pores (e.g., average diameter≈42nm) onto silicon. In this work, roughness is reduced to sub-10nm levels, which is in par with plasma etching, by decreasing pore size of the catalyst via dealloying in far-from equilibrium conditions. At this level, single-digit nanometric details such as grain-boundary grooves of the catalyst are imprinted and attributed to the resolution limit of Mac-Imprint, which is argued to be twice the Debye length (i.e., 1.7nm)-a finding that broadly applies to metal-assisted chemical etching. Last, Mac-Imprint is employed to produce single-mode rib-waveguides on pre-patterned silicon-on-insulator wafers with root-mean-square line-edge roughness less than 10nm while providing depth uniformity (i.e., 42.9±5.5nm), and limited levels of silicon defect formation (e.g., Raman peak shift<0.1cm-1 ) and sidewall scattering.

Domain morphology and electro-optic effect in Si-integrated epitaxial BaTiO3 films

Ferroelectric $\mathrm{BaTi}{\mathrm{O}}_{3}$ thin films epitaxially integrated on Si are an emergent platform for fabricating integrated electro-optical modulators using the linear electro-optic effect for applications in silicon photonics. These devices hold great promise for optical neuromorphic and quantum computing. Understanding the domain morphology of such films is essential for building ultrafast, ultralow-power electro-optic modulators. However, the domain morphology of the film is marked by significant complexity and our knowledge of it and its relation to the electro-optic response in epitaxial thin films is limited. In this paper, we use a phase-field model implemented within the finite-element method to map domain morphologies. The corresponding electro-optic response is also discussed.

Special issue “optical communications, sensing, and laser applications”

Special issue “optical communications, sensing, and laser applications”

Optical and Mechanical Properties of Europium-Doped Silicon Oxynitride Thin Films

Light emission from silicon-based systems has gained significant interest over the past few decades with the vision of developing an optoelectronic platform that can be integrated with the existing metal-oxide-semiconductor (MOS) technology [1]. Rare earth doping of silicon-based materials is a promising approach to fabricating efficient light emitting devices because of their excellent luminescence properties and their chemical stability [2]. Europium (Eu) ions are attractive dopants for silicon photonic applications due to their intense emission in the visible spectral region. The efficiency of such photonic devices can be influenced by the mechanical properties of the Eu-doped films. Thus, the integration of these films in photonic devices requires an understanding of their mechanical properties as well. In this work, we discuss the relationship between the photoluminescence (PL) behavior and the elasticity and hardness of Eu doped silicon oxynitride (SiON) thin films.We have fabricated thin films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition system with integrated magnetron sputtering system [3] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon) and nitrogen (diluted in 90% argon) were used as precursor gases, while a 99.9% pure Eu sputtering target was used as a sputtering source. Different sets of samples were fabricated by changing the sputtering power and argon flow rate to understand the effect of deposition parameters on the dopant concentration and the optical and mechanical properties. Post-deposition annealing in nitrogen and a mixture of nitrogen with hydrogen (5%) were performed over a wide range of temperatures from 600° to 1100° C. The effect of hydrogen passivation was studied as well. The atomic concentration of the constituents was identified by Rutherford backscattering spectrometry. Optical properties were investigated by variable angle spectroscopic ellipsometry (VASE) analysis. The PL spectra were obtained at room temperature with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiON films with the incorporation of Eu. The indentation hardness and Young’s modulus of the films were investigated, respectively, for different Eu concentrations and different deposition parameters.Reference[1] A. Moadhen, H. Elhouichet, M. Oueslati, and M. Férid, “Photoluminescence properties of europium-doped porous silicon nanocomposites,” J. Lumin., vol. 99, no. 1, pp. 13–17, 2002, doi: 10.1016/S0022-2313(02)00322-8.[2] Z. Lin R. Huang, H. Wang, Y. Wang, Y. Zhang, Y. Gao, J. Song, C. Song, H. Li, “Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films,” J. Alloys Compd., vol. 694, pp. 946–951, 2017, doi: 10.1016/j.jallcom.2016.10.132.[3] J. W. Miller, Z. Khatami, J. Wojcik, J. D. B. Bradley, and P. Mascher, “Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials,” Surf. Coatings Technol., vol. 336, pp. 99–105, 2018, doi: 10.1016/j.surfcoat.2017.08.051.

Free-Space Applications of Silicon Photonics: A Review.

Silicon photonics has recently expanded its applications to delivering free-space emissions for detecting or manipulating external objects. The most notable example is the silicon optical phased array, which can steer a free-space beam to achieve a chip-scale solid-state LiDAR. Other examples include free-space optical communication, quantum photonics, imaging systems, and optogenetic probes. In contrast to the conventional optical system consisting of bulk optics, silicon photonics miniaturizes an optical system into a photonic chip with many functional waveguiding components. By leveraging the mature and monolithic CMOS process, silicon photonics enables high-volume production, scalability, reconfigurability, and parallelism. In this paper, we review the recent advances in beam steering technologies based on silicon photonics, including optical phased arrays, focal plane arrays, and dispersive grating diffraction. Various beam-shaping technologies for generating collimated, focused, Bessel, and vortex beams are also discussed. We conclude with an outlook of the promises and challenges for the free-space applications of silicon photonics.

ITO film stack engineering for low-loss silicon optical modulators

The Indium Tin Oxide (ITO) platform is one of the promising solutions for state-of-the-art integrated optical modulators towards low-loss silicon photonics applications. One of the key challenges on this way is to optimize ITO-based thin films stacks for electro-optic modulators with both high extinction ratio and low insertion loss. In this paper we demonstrate the e-beam evaporation technology of 20 nm-thick ITO films with low extinction coefficient of 0.14 (Nc = 3.7·1020 cm−3) at 1550 nm wavelength and wide range of carrier concentrations (from 1 to 10 × 1020 cm−3). We investigate ITO films with amorphous, heterogeneously crystalline, homogeneously crystalline with hidden coarse grains and pronounced coarsely crystalline structure to achieve the desired optical and electrical parameters. Here we report the mechanism of oxygen migration in ITO film crystallization based on observed morphological features under low-energy growth conditions. Finally, we experimentally compare the current–voltage and optical characteristics of three electro-optic active elements based on ITO film stacks and reach strong ITO dielectric permittivity variation induced by charge accumulation/depletion (Δn = 0.199, Δk = 0.240 at λ = 1550 nm under ± 16 V). Our simulations and experimental results demonstrate the unique potential to create integrated GHz-range electro-optical modulators with sub-dB losses.

Design and demonstration of an efficient pump rejection filter for silicon photonic applications.

Photon pair generation via spontaneous four-wave mixing in silicon waveguides/microring resonators integrated with a high extinction pump rejection filter is very much in demand for futuristic large-scale integrated quantum photonics circuits. Ideally, a distributed Bragg reflector (DBR) can be designed to offer desired pump rejection. However, fabricated DBRs suffer degradation in pump extinction due to roughness-induced unwanted scattering waves in the forward direction around the Bragg wavelength. It is therefore inferred that the roughness-induced forward scattering can be reduced significantly by integrating a DBR structure in one of the sidewalls (instead of two sidewalls) of a multimode rib waveguide (instead of a single mode strip waveguide). Therefore, we studied a single-stage DBR filter with this design which exhibits a significantly higher stop band extinction (∼63 dB), in comparison with that of earlier reported results (<50 dB). To validate the pump rejection efficiency of such fabricated devices in quantum photonic applications, we have carried out on-chip stimulated four-wave mixing experiments and shown that the pump laser within the rejection band could be attenuated to the level of idler power.

InAsP Quantum Dot-Embedded InP Nanowires toward Silicon Photonic Applications

Quantum dot (QD) emitters on silicon platforms have been considered as a fascinating approach to building next-generation quantum light sources toward unbreakable secure communications. However, it has been challenging to integrate position-controlled QDs operating at the telecom band, which is a crucial requirement for practical applications. Here, we report monolithically integrated InAsP QDs embedded in InP nanowires on silicon. The positions of QD nanowires are predetermined by the lithography of gold catalysts, and the 3D geometry of nanowire heterostructures is precisely controlled. The InAsP QD forms atomically sharp interfaces with surrounding InP nanowires, which is in situ passivated by InP shells. The linewidths of the excitonic (X) and biexcitonic (XX) emissions from the QD and their power-dependent peak intensities reveal that the proposed QD-in-nanowire structure could be utilized as a non-classical light source that operates at silicon-transparent wavelengths, showing a great potential for diverse quantum optical and silicon photonic applications.

A new direct band gap Si-Ge allotrope with advanced electronic and optical properties.

Direct-band silicon materials have been a sought-after material for potential applications in silicon photonics and solar cells. Accordingly, methodologies like nanostructure engineering, alloy engineering and strain engineering have been developed. In this work, the particle swarm optimization (PSO) algorithm is used to design direct-band Si-Ge alloys. The findings of phonon computations demonstrate that all these structures are dynamically stable. In addition, ab initio molecular dynamics and elastic constant calculations are carried out, with results indicating these structures are thermodynamically stable at 300 K, as well as being mechanically stable. All of these materials exhibit semiconductor behavior with band gaps of 1.03, 0.68 and 1.37 eV for α, β and γ phases, respectively, at the HSE06 level. The results of effective mass and mobility of carriers that are important in applications show that holes are more easily transported in all structures, with higher concentration of holes accompanied by lower carrier mobility. Different concentrations of holes nh lead to different limits in the scattering process. When nh is lower than the value of around 1016 cm-3, deformation potential scattering is dominant, while the ionized impurity scattering process limits overall mobility when nh is higher than such a value. Finally, the absorption spectra shows that both α and β phases have isotropic optical properties in the X- and Y-directions while strong anisotropy can be seen in the Z-direction. However, the γ phase exhibits no notable isotropy. This investigation finds three direct-band and potentially CMOS compatible materials, a finding which will benefit the development of high efficiency emitters or solar cells.