Si-based Photonic Devices Research Articles

Tuning the light emission of a Si micropillar quantum dot light-emitting device array with the strain coupling effect

Using an optical signal to realize sensing of a strain signal is a promising application for tactile sensors. However, most research is now focused on piezophototronic LED arrays, which are difficult to incorporate into the Si-based semiconductor industry. Due to the poor photoelectric performance of Si-based devices caused by the indirect band gap of Si, it has always been challenging to construct high density light-emitting devices with Si. Here, a Si-based quantum dot light-emitting device (QLED) array composed of p-Si micropillars is designed and fabricated, and the mechanism for modulation of the strain coupling effect in Si on the electroluminescence performance of Si-based QLEDs is studied. The introduction of QDs easily provides efficient and adjustable light emission and meets the requirements of different practical applications. The emission intensity of the QLED depends on the injected current density, and the transportation processes of the carriers can be modulated by the strain coupling effect. The combination of Si-based photonic devices with pressure sensing may have a significant impact on the fields of electronic skin and human‒machine interfaces. More importantly, this technology is fully compatible with the dominant Si-based semiconductor industry. Therefore, it shows promise in realizing the integration of large-scale Si-based photonic devices and expanding their application fields.

Low Threshold GaN-Based Microdisk Lasers on Silicon With High Q Factor

III-nitride-based microdisk lasers on Si offer the potential in large-scale monolithic Si-based photonic integrated circuits. Here, we demonstrate a new approach to fabricating III-nitride microdisk lasers on Si, which can avoid the problem of low crystal quality and large thickness in traditional Si-based photonic devices. The III-nitride membrane was grown on a sapphire substrate and then transferred to Si to fabricate the microdisk lasers; and an airgap undercut structure was realized by simply wet etching of a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sacrificial layer. Devices fabricated by this method are free from the defect-rich layers that are unavoidable when grown directly on Si, resulting in a high quality (Q) value of 12543 at 412.9 nm. Room temperature lasing was demonstrated with a threshold energy density as low as 33.6 μJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The whispering gallery mode oscillation was clearly observed and the model behavior was systematically investigated.

Millimeter-scale growth of highly ordered CsPbBr3 single-crystalline microplatelets on SiO2/Si substrate by chemical vapor deposition

Recently, all-inorganic cesium lead bromide (CsPbBr3) perovskite has attracted tremendous interest due to its promise for green light photonic and optoelectronic devices. The growth of high-quality planar micro-/nano-structures of CsPbBr3 on the technologically important silicon substrate is an important issue for these applications, which has not yet been well explored. Herein we fabricate millimeter-scale single-crystalline CsPbBr3 microplatelets (MPs) on SiO2/Si substrate by chemical vapor deposition. A preferred growth direction is demonstrated with the [110] direction parallel to the flux direction of carrier gas. Strong green emission is observed at room temperature with superior photo-stability, long lifetime, and excitonic features. Furthermore, the room temperature whispering-gallery-mode lasing is achieved from the focused ion beam fabricated microdisks with the thresholds comparable to those of pristine square MPs. These results suggest the great potentials of CsPbBr3 MPs for the Si-based photonic devices.

Influence of the spatial extent of the space-charge region in c-Si on the electric-field-induced second-harmonic-generation effect

Second-harmonic-generation (SHG) spectroscopy can be used as an all-optical probe of space-charge regions (SCR) in semiconductors such as c - S i by exploiting the electric-field-induced second-harmonic-generation (EFISH) effect. To do so accurately, a thorough understanding of the EFISH effect is needed, and here a detailed model is presented, taking into account the so-far neglected spatial extent of the SCR on the spectral shape of the EFISH contribution. This shows that the spatial extent causes a significant phase shift in the EFISH contribution ranging from 0.1 π r a d to 0.4 π r a d with decreasing SCR strength. This predicted phase shift was verified by dedicated measurements of the spectral SHG phase and intensity of a series of samples covering the typical range of SCR strengths. The spectral SHG response of these samples indeed showed the predicted phase shift in the EFISH contribution and demonstrated that the extent of the SCR cannot be neglected. The obtained insights can result in improved accuracy in the determination of built-in charges near a c - S i interface, which is of interest in the context of semiconductor devices using SHG spectroscopy. Moreover, this refined understanding of the EFISH effect is beneficial in SHG experiments on 2D materials with c - S i serving as a substrate of Si-based photonic devices.

Selectively Grown III-V Lasers for Integrated Si-Photonics

Epitaxially integrating III-V lasers with Si-photonics is the key for compact, efficient, and scalable photonic integrated circuits (PICs). Here we present an investigation of a path forward in integrating III-V functionalities on industry-standard silicon-on-insulator (SOI) platforms using selective area hetero-epitaxy. Based on our recently developed methods of selectively growing device quality InP on (001)-oriented SOI wafers, we demonstrated InP stripes and segments, with dimensions varying from a few hundred nanometers to a few micrometers. The flexible epitaxy of InP on SOI together with the unique “bufferless” trait will enable efficient light interfacing with Si-based photonic devices using either evanescent or butt coupling schemes. We simulated the possibility of employing the micrometer-scale InP on insulator to realize electrically driven lasers and found that the metal induced optical loss is negligible when the InP dimension exceeds 4.0 μm. The potential of utilizing this selective area growth method to realize fully integrated Si-photonics is illustrated.

Bufferless 1.5 µm III-V lasers grown on Si-photonics 220 nm silicon-on-insulator platforms

Efficient III-V lasers directly grown on Si remain the “holy grail” for present Si-photonics research. In particular, a bufferless III-V laser grown on the Si-photonics 220 nm silicon-on-insulator (SOI) platform could seamlessly bridge the active III-V light sources with the passive Si-based photonic devices. Here we report on the direct growth of bufferless 1.5 µm III-V lasers on industry-standard 220 nm SOI platforms using metal organic chemical vapor deposition (MOCVD). Taking advantage of the constituent diffusivity at elevated growth temperatures, we first devised a MOCVD growth scheme for the direct hetero-epitaxy of high-quality III-V alloys on the 220 nm SOI wafers through synergizing the conventional aspect ratio trapping (ART) and the lateral ART methods. In contrast to prevalent epitaxy inside V-grooved pockets, our method features epitaxy inside trapezoidal troughs and thus enables the flexible integration of different III-V compounds on SOIs with different Si device layer thicknesses. Then, using InP as an example, we detailed the growth process and performed extensive study of the crystalline quality of the epitaxial III-V. Finally, we designed and fabricated both pure InP and InP/InGaAs lasers, and we achieved room-temperature lasing in both the 900 nm band and the 1500 nm band under pulsed optical excitation. Direct epitaxy of these in-plane and bufferless 1.5 µm III-V lasers on the 220 nm SOI platform suggests the imminent interfacing with Si-based photonic devices and the subsequent realization of fully integrated Si-based photonic circuits.

Defect engineering for high quality InP epitaxially grown on on-axis (001) Si

Heteroepitaxy of indium phosphide (InP) and its lattice-matched alloys on silicon (Si) show great promise for Si-based optoelectronic devices and photonic integrated circuits. Here, we report the monolithic growth of high crystalline quality InP on V-groove patterned (001) Si substrates by metalorganic chemical vapor deposition, demonstrating a low surface defect density of 4.5 × 107 cm−2, characterized by statistical electron channel contrast imaging. This advanced InP-on-Si virtual substrate is implemented by combining a compositionally graded indium gallium arsenide (InxGa1 − xAs) buffer and optimized In0.73Ga0.27As/InP strained-layer superlattices on gallium arsenide on a V-grooved Si template. These techniques gradually accommodate the lattice mismatch and effectively filter most of the generated dislocations. A comprehensive material characterization and the demonstration of room-temperature continuous-wave electrically pumped laser diodes on Si validate the suitability of using this InP-on-Si platform for monolithic integration of InP- and Si-based electronic and photonic devices.

MOCVD grown low dislocation density GaAs-on-V-groove patterned (001) Si for 1.3 μ m quantum dot laser applications

We report the development of gallium arsenide (GaAs) films grown on V-groove patterned (001) silicon (Si) by metalorganic chemical vapor deposition. This technique can provide an advanced virtual substrate platform for photonic integrated circuits on Si. A low defect density of 9.1 × 106 cm−2 was achieved with the aspect ratio trapping capability of the V-grooved Si and dislocation filtering approaches including thermal cycle annealing and dislocation filter layers. The efficiencies of these dislocation reduction methods are quantified by statistical electron channeling contrast imaging characterization. Meanwhile, different sets of dislocation filtering layers are evaluated and optimized. To further demonstrate the suitability of GaAs on the V-grooved Si technique for Si-based photonic devices, especially for the appealing 1.3 μm quantum dot (QD) lasers, a 7-layer indium arsenide QD structure was grown on both GaAs-on-V-grooved Si and native GaAs substrates. The same photoluminescence intensity and full-width at half-maximum values were observed for both structures. The optimization methodology in this work therefore offers a feasible approach to realize high quality III–V materials on Si for large-scale integration.

Nonlinear optical absorption of beryllium isoelectronic centers doped in silicon waveguides

Impurities provide host materials with additional optical functionalities. In this study, we observed the nonlinear optical absorption of beryllium isoelectronic centers (Be-IECs) doped in silicon waveguides (WGs) with optical population control of their bound exciton states. The optimized fabrication based on ion implantation and rapid thermal annealing achieved Be-IEC doping with a high concentration. The bound exciton state localized at the doped Be-IECs shows a photoluminescence peak and optical absorption simultaneously at a wavelength of 1150 nm. Nonresonant optical pumping at a power of ∼70 μW reduces the optical absorption coefficient of a Be-doped WG by 1.3 cm−1, which is one third of the intrinsic absorption. This significant reduction is attributed to the suppression of the absorption transition to the discrete bound exciton state filled by optical pumping. The nonlinear optical absorption of these impurity centers makes it possible to expand the potential application of Si-based photonic devices for enabling all-optical switching with lower optical power.

A facile method for bright, colour-tunable light-emitting diodes based on Ga-doped ZnO nanorods

Bottom-up fabrication of nanowire-based devices is highly attractive for oxide photonic devices because of high light extraction efficiency; however, unsatisfactory electrical injection into ZnO and poor carrier transport properties of nanowires severely limit their practical applications. Here, we demonstrate that ZnO nanorods doped with Ga donors by in situ dopant incorporation during vapour–solid growth exhibit superior optoelectronic properties that exceed those currently synthesised by chemical vapour deposition, and accordingly can be electrically integrated into Si-based photonic devices. Significantly, the doping method was found to improve the nanorod quality by decreasing the concentration of point defects. Light-emitting diodes (LEDs) fabricated from the Ga-doped ZnO nanorod/p-Si heterojunction display bright and colour-tunable electroluminescence (EL). These nanorod LEDs possess a dramatically enhanced performance and an order of magnitude higher EL compared with equivalent devices fabricated with undoped nanorods. These results point to an effective route for large-scale fabrication of conductive, single-crystalline ZnO nanorods for photonic and optoelectronic applications.

Nano-SiC region formation in (100) Si-on-insulator substrate: Optimization of hot-C+-ion implantation process to improve photoluminescence intensity

We experimentally studied the optimization of the hot-C+-ion implantation process for forming nano-SiC (silicon carbide) regions in a (100) Si-on-insulator substrate at various hot-C+-ion implantation temperatures and C+ ion doses to improve photoluminescence (PL) intensity for future Si-based photonic devices. We successfully optimized the process by hot-C+-ion implantation at a temperature of about 700 °C and a C+ ion dose of approximately 4 × 1016 cm−2 to realize a high intensity of PL emitted from an approximately 1.5-nm-thick C atom segregation layer near the surface-oxide/Si interface. Moreover, atom probe tomography showed that implanted C atoms cluster in the Si layer and near the oxide/Si interface; thus, the C content locally condenses even in the C atom segregation layer, which leads to SiC formation. Corrector-spherical aberration transmission electron microscopy also showed that both 4H-SiC and 3C-SiC nanoareas near both the surface-oxide/Si and buried-oxide/Si interfaces partially grow into the oxide layer, and the observed PL photons are mainly emitted from the surface SiC nano areas.

Nonlinear optical absorption and ultrafast optical response of un-doped and P-doped nanocrystalline Si/SiO2 multilayers

The nonlinear optical properties and ultrafast optical response of Si/SiO2 multilayers with and without phosphorus doping are comparatively studied in the present work. The enhanced nonlinear absorption and fast recombination process were observed after phosphorus doping, the defect states generated by high phosphorus doping was the possible origination. It was suggested that the nonlinear optical repose as well as the ultrafast dynamic process could be changed greatly via phosphorous doping, which provided a new approach to improve the performance of Si-based photonic devices.

Characterization of a Ge1-x-ySiySnx/Ge1-xSnx multiple quantum well structure grown by sputtering epitaxy.

A high-quality Ge0.88Si0.08Sn0.04/Ge0.94Sn0.06 multiple quantum well (MQW) structure was grown on a Ge (001) substrate by sputtering epitaxy. The MQW structure was characterized by high-resolution x-ray diffraction and transmission electron microscopy. Surface-illuminated Ge0.88Si0.08Sn0.04/Ge0.94Sn0.06 MQW pin photodetectors were fabricated with cutoff wavelengths of up to 2140nm. The analysis of transitions from spectral response was fitted well with the theoretical calculations. Results suggest that sputtering epitaxy is a promising method for preparing high-quality low-dimensional Sn-based group IV materials and that Ge1-x-ySiySnx/Ge1-xSnx MQWs have potential applications in the development of efficient Si-based photonic devices.

Plasmonic Bowtie Nanolaser Arrays

Plasmonic lasers exploit strong electromagnetic field confinement at dimensions well below the diffraction limit. However, lasing from an electromagnetic hot spot supported by discrete, coupled metal nanoparticles (NPs) has not been explicitly demonstrated to date. We present a new design for a room-temperature nanolaser based on three-dimensional (3D) Au bowtie NPs supported by an organic gain material. The extreme field compression, and thus ultrasmall mode volume, within the bowtie gaps produced laser oscillations at the localized plasmon resonance gap mode of the 3D bowties. Transient absorption measurements confirmed ultrafast resonant energy transfer between photoexcited dye molecules and gap plasmons on the picosecond time scale. These plasmonic nanolasers are anticipated to be readily integrated into Si-based photonic devices, all-optical circuits, and nanoscale biosensors.

The optical property of tensile-strained n-type doped Ge

Tensile-strained germanium is one of the promsing materials for Si-based photonic devices due to its quasi-direct band and compatiblility with silicon technology. The band structure of tensile-strained germanium is investigated based on the theory of van de Walle deformed potential. The carrier distributions in the conduction bands at Γ and L vallies under the strain, and the n-type doping concentratoin in germanium are analyzed. Considering the competition between radiative recombinations at Γ and L vallies and Auger recombination, as well as dislocation induced non-radiative recombination, internal quantum efficiency and optical gain for direct band transition in n-type Ge are calculated. It is shown that 74.6% internal quantum efficiency can be obtained in the 1.5% tensile-strained n-type doped Ge under carrier injection and a strong optical gain is predicted, which is comparable to those of III-V materials.

Mid infrared band gap properties of 3-dimensional silicon inverse opal photonic crystal

By the solvent vaporization convection self-assembly method, 1.86 μm silica microspheres were assembled into a colloidal crystal template with long-range order. High refractive index silicon was then filled in the voids of the silica template by the low pressure chemical vapor deposition method. A 3-dimensional silicon inverse opal photonic crystal was obtained with a photonic band gap simulated by a plane wave expansion method. Its micro modality and photonic band gap properties were characterized by scanning electron microscopy and Fourier transform IR spectrometer. There was a good agreement between the measured spectra and the simulated results. The tilt-angle reflectance spectra showed that an obvious reflection peak at 3319 nm stayed in existence with different incidence directions. This result proved that silicon inverse opal has a complete photonic band gap in the mid infrared range. This study opens up an opportunity to create Si-based photonic crystal devices for atmosphere mid infrared photodetection.

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO2 films implanted by different doses of Si+ ions. Room-temperature PL from 400-nm-thick SiO2 films implanted to a dose of 3×1016 cm−2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950–1150 °C) and duration (5–20 s). The reported approach of implanting silicon into SiO2 films followed by RTA may be effective for tuning Si-based photonic devices.

Recent Progresses of Si-Based Photonics in Chinese Main Land

Si-based photonic materials and devices, including SiGe/Si quantum structures, SOI and InGaAs bonded on Si, PL of Si nanocrystals, SOI photonic crystal filter, Si based RCE (Resonant Cavity Enhanced) photodiodes, SOI TO (thermai-optical) switch matrix were investigated in Institute of Serniconductors, Chinese Academy of Sciences. The main results in recent years are presented in the paper. The mechanism of PL from Si NCs embedded in SiO2 matrix was studied, a greater contribution of the interface state recombination (PL peak in 850 similar to 900 nm) is associated with larger Si NCs and higher interface state density. Ge dots with density of order of 10(11) cm(-2) were obtained by UHV/CVD growth and 193 nm excimer laser annealing. SOI photonic crystal filter with resonant wavelength of 1598 nm and Q factor of 1140 was designed and made. Si based hybrid InGaAs RCE PD with eta of 34.4% and FWHM of 27 nut were achieved by MOCVD growth and bonding technology between InGaAs epitaxial and Si wafers. A 16x16 SOI optical switch matrix were designed and made. A new current driving circuit was used to improve the response speed of a 4x4 SOI rearrangeable nonblocking TO switch matrix, rising and failing time is 970 and 750 ns, respectively.

FDTD Analysis of Two-Photon Absorption and Free-Carrier Absorption in Si High-Index-Contrast Waveguides

The two-photon absorption (TPA), the free-carrier absorption (FCA), and the carrier plasma effect play important roles in Si-based photonic devices. These effects have been incorporated directly into a finite-difference time-domain (FDTD) simulator for the first time. To check the validity of the FDTD simulator, it has been applied to the simulation of nonlinear transmission of an ultrashort optical pulse in a short Si high-index-contrast waveguide. The results are consistent with those shown in the literature. The cause of the slight negative slope transmission has been explained as follows. Since the TPA-induced FCA makes the pulse-shape asymmetric, a pulse with a higher optical input intensity tends to have a longer tail. Therefore, a stronger optical pulse is subject to FCA for a longer period, resulting in the negative differential transmission.

Silicon nanocrystals in silica—Novel active waveguides for nanophotonics

Nanophotonic structures combining electronic confinement in nanocrystals with photon confinement in photonic structures are potential building blocks of future Si-based photonic devices. Here, we present a detailed optical investigation of active planar waveguides fabricated by Si +-ion implantation (400 keV, fluences from 3 to 6×10 17 cm −2) of fused silica and thermally oxidized Si wafers. Si nanocrystals formed after annealing emit red-IR photoluminescence (PL) (under UV-blue excitation) and define a layer of high refractive index that guides part of the PL emission. Light from external sources can also be coupled into the waveguides (directly to the polished edge facet or from the surface by applying a quartz prism coupler). In both cases the optical emission from the sample facet exhibits narrow polarization-resolved transverse electric and transverse magnetic modes instead of the usual broad spectra characteristic of Si nanocrystals. This effect is explained by a theoretical model which identifies the microcavity-like peaks as leaking modes propagating below the waveguide/substrate boundary. We present also permanent changes induced by intense femtosecond laser exposure, which can be applied to write structures like gratings into the Si-nanocrystalline waveguides. Finally, we discuss the potential for application of these unconventional and relatively simple all-silicon nanostructures in future photonic devices.