This paper reviews our recent progress on silicon (Si) pn junction light emitting diodes with locally doping engineered carrier potentials. Boron implanted Si diodes with dislocation loops have electroluminescence (EL) quantum efficiency up to 0.12%, which is two orders of magnitude higher than those without dislocations. Boron gettering along the strained dislocation lines produces locally p-type spike doping at the dislocations, which have potential wells for bounding spatially indirect excitons. Thermal dissociation of the bound excitons releases free carriers, leading to an anomalous increase of the band to band luminescence with increasing temperature. Si light emitting diodes with external quantum efficiency of 0.2% have been also demonstrated by implementation of pnpn modulation doping arrays.

Si photonics becomes one of the research focuses in the field of photonics. Si-based light-emitting devices are one of the most important devices in this field. In this paper, we review the Si-based light-emitting devices fabricated by embedding Ge self-assembled quantum dots into optical microcavities. Ge self-assembled quantum dots emit light in the telecommunication wavelength range from 1.3 to 1.6 μm, for which Si is transparent. Ge self-assembled quantum dots were grown on silicon-on-insulator (SOI) by molecular beam epitaxy (MBE) in Stranski-Krastanov (S-K) mode. Then, electron beam lithography (EBL) was used to define the pattern of optical microcavities on the wafer. Finally, the pattern was transferred onto the Si/Ge slab by inductive coupled plasma (ICP) dry etching. Room-temperature photoluminescence (PL) was used to characterize the light-emitting properties of fabricated devices. The results showed that strong resonant light emission was observed in different optical microcavities. Significant enhancement of the intensity was obtained by the optical resonance. Based on the results of PL, we designed and fabricated current-injected light-emitting devices based on Ge self-assembled quantum dots in optical microcavities. Room-temperature resonant light emission was observed from Ge dots in a 3.8 μm microdisk resonator.

Photonic crystal (PhC) has offered a powerful means to mold the flow of light and manipulate light-matter interaction at subwavelength scale. Silicon has a large refraction index and low loss in infrared wavelengths, which makes it an important optical material. And silicon has been widely used for integrated photonics applications. In this paper, we have reviewed some recent theoretical and experimental works in our group on infrared two-dimensional (2D) air-bridged silicon PhC slab devices that are based on both band gap and band structure engineering. We have designed, fabricated, and characterized a series of PhC waveguides with novel geometries, PhC high-quality (high-Q) cavity, and channel drop filters utilizing resonant coupling between waveguide and cavity. These devices are aimed to construct a more flexible network of transport channel for infrared light at micrometer/nanometer scale. We have also explored the remarkable dispersion properties of PhCs by engineering the band structures to achieve negative refraction, self-collimation, superprism, and other anomalous dispersion behaviors of infrared light beam. Furthermore, we have designed and fabricated a PhC structure with negative refraction effect and used scanning near-field optical microscopy to observe the negative refraction beam. Finally, we have designed and realized a PhC structure that exhibits a self-collimation effect in a wide angle range and with a large bandwidth. Our works presented in this review show that PhCs have a strong power of controlling propagation of light at micrometer/nanometer scale and possess a great potential of applications in integrated photonic circuits.

This paper reviews the recent progress in photonic devices application of Ge-on-Si. Ge-on-Si materials and optical devices are suitable candidates for Si-based optoelectronic integration because of the mature epitaxial technique and the compatibility with Si complementary metal-oxide-semiconductor (CMOS) technology. Recently, the realities of electric-pump Ge light emitting diode (LED) and optical-pump pulse Ge laser, Ge quantum well modulator based on quantum Stark confined effect, waveguide Ge modulator based on Franz-Keldysh (FK) effect, and high performance near-infrared Ge detector, rendered the Si-based optoelectronic integration using Ge photonic devices. Ge-on-Si material is also an important platform to grow other materials on it for Si-based optoelectronic integration. InGaAs and GeSn have been grown on the Ge-on-Si. InGaAs LED and GeSn photodetector have been successfully fabricated as well.

Surface plasmon polariton (SPP) is an attractive candidate to improve internal quantum efficiency (QE) of spontaneous emission (SE) from nano-structured silicon (Si) including nano-porous silicon (NP-Si) and silicon nanocrystal (Si-NC). Since the SPP resonant frequency of common metals, e.g., gold (Au), silver (Ag), copper (Cu), and aluminum (Al), is too high, the SPP resonance has to be engineered to match the luminescence from nano-structured Si. For this purpose, we have proposed and demonstrated three approaches including metal-rich Au(1-α)-SiO₂(α) cermet SPP waveguide (WG), compound layer structure WG and metallic grating. In this paper, those approaches are reviewed and discussed. According to the calculated results, such three methods could effectively enhance SE rate from NP-Si or Si-NCs and show potential in developing high efficiency Si based light sources with electric pump.

This study uses a dipole embedded in Al₂O₃ layer to excite a symmetric surface plasmon polariton (SPP) mode in Au/Al₂O₃/Au waveguide to investigate its profile properties by using finite-difference time-domain (FDTD) method. The excited dipole decay radiatively direct near-field coupling to SPP mode owing to thin Al₂O₃ layer of 100 nm. The effects of electric and magnetic field intensity profiles and decay length have been considered and characterized. It is found that dipole location is an important factor to influence the horizontal and vertical profile properties of symmetric SPP mode in Au/Al₂O₃/Au waveguide. The amplitudes of electric and magnetic field intensity and the wavelengths of metal-insulator-metal (MIM) SPP resonance mode can be tuned by varying dipole location. The horizontal and vertical decay lengths are 19 and 24 nm, respectively. It is expected that the Au/Al₂O₃/Au waveguide structure is very useful for the practical applications of designing a SPP source.

A hybrid plasmonic waveguide containing silicon core, silver cap and ultra-thin sandwiched SiO₂ layer is studied. By analyzing the mode distribution patterns and the curves of mode effective index, we show how the plasmonic mode around the metal surface is coupled with the fundamental mode in the silicon core to form a squeezed hybrid mode. The ability of the hybrid plasmonic waveguide in energy confinement is also discussed quantitatively.

A new type of Si waveguide wrapped by silicon nitride (SiN) is designed, and its optical and thermal analysis are presented. The thickness of SiN up-cladding should be larger than 1 μm in order to prevent the absorption of optical field by metal heater. Thermal response of the proposed waveguide structure is enhanced by the high thermal conductivity of SiN. Moreover, this thermal response can be further improved by a fast heat dissipation channel created in this structure. Our simulation results indicate that a rise time of about 110 ns can be achieved for the proposed waveguide structure, which is about two orders of magnitude less than that of the conventional Si waveguide. The influences of the thickness of up-cladding and the stretching width and etching depth on the thermal performance are also discussed. The simulation shows thin up-cladding, large stretching width and etching depth are critical to enhance the thermal response speed.

In this paper, a binary blazed grating-based polarization independent filter on silicon on insulator (SOI) under full conical incidence is presented. The properties of the grating filter are investigated by rigorous coupled-wave analysis. It’s shown that the filter demonstrates high reflectivity (R>99%) at its resonant wavelength, which stays the same under three different polarization states. It indicates that this grating filter is polarization-independent. The final data shows its polarization-dependent loss (PDL) is only 0.04 dB and the full width at half maximums (FWHMs) of the transverse electric (TE-) and transverse magnetic (TM-) polarized light are 0.24 and 0.46 nm, respectively.

We focus on the optimization of SiGe material deposition, the minimization of the parasitic capacitance of the probe pads for high speed, low voltage and high contrast ratio operation. The device fabrication is based on processes for standard Si electronics and is suitable for mass-production. We present observations of quantum confinement and quantum-confined Stark effect (QCSE) electroabsorption in Ge quantum wells (QWs) with SiGe barriers grown on Si substrates. Though Ge is an indirect gap semiconductor, the resulting effects are at least as clear and strong as seen in typical III–V QW structures at similar wavelengths. We also demonstrated a modulator, with eye diagrams of up to 3.5 GHz, a small driving voltage of 2.5 V and a modulation bandwidth at about 10 GHz. Finally, carrier dynamics under ultra-fast laser excitation and high-speed photocurrent response are investigated.

Silicon based optical modulators with improved extinction ratio (ER) of 25 dB were demonstrated on complementary metal oxide semiconductor (CMOS) platform. It was proposed that the effect of optical absorption due to free carriers accumulated in silicon should be considered in the analysis of device configuration. Experimental results presented in this study were identical with the proposed analyses. The modulators were operated with the data transmission rate of 3.2 Gbps.

We propose a unidirectional emission silicon/III-V laser, which comprises an III-V quantum wells microdisk connected to an output waveguide and a silicon-on-insulator (SOI) waveguide. Characteristics of the III-V microdisk with an output waveguide and mode coupling between the III-V output waveguide and the SOI waveguide are investigated by three-dimensional (3D) finite-difference time-domain (FDTD) method. Simulation results show that the Q factor of a coupled mode for a 7.5 μm diameter microdisk connected to a 0.5 μm wide output waveguide is about 8.5×10⁴. And the coupling efficiency between the III-V output waveguide and the SOI waveguide is over 96% when the III-V waveguide width is 0.5 μm, the SOI waveguide width is 0.565 μm and the vertical gap between those two waveguides is 0.1 μm. The proposed hybrid laser would be of valuable applications for on-chip interconnects.

We propose and numerically demonstrate an ultrafast real-time ordinary differential equation (ODE) computing unit in optical field based on a silicon microring resonator, operating in the critical coupling region as an optical temporal differentiator. As basic building blocks of a signal processing system, a subtractor and a splitter are included in the proposed structure. This scheme is featured with high speed, compact size and integration on a silicon-on-insulator (SOI) wafer. The size of this computing unit is only 35 μm × 45 μm. In this paper, the performance of the proposed structure is theoretically studied and analyzed by numerical simulations.

A series of Si-rich amorphous silicon carbide (a-SiC:H) thin films were deposited in conventional plasma enhanced chemical vapor deposition system with various gas ratio R = [CH₄]/[SiH₄]. The microstructural, optical and electronic properties of as-deposited films were investigated in this study. It was found that optical band gap was linearly proportional to carbon content in the films and it could be controlled in a range of 1.8–2.4 eV by changing the gas ratio, R. Both dark and photo conductivities in room temperature were decreased with the increasing of carbon content in the films, and the photosensitivity reached as high as 10⁴ for the film with the optical band gap of 1.96 eV. The as-deposited samples were subsequently annealed at the temperatures of 900°C and 1000°C. The formation of nanocrystalline silicon (nc-Si) dots in amorphous silicon carbide (a-SiC) host matrix was shown. The dark conductivity was enhanced by five orders of magnitude after annealing compared with that of as-deposited films. The result of temperature-dependent conductivity suggested that the property of carrier transport was dominated by conduction process between the extended states. Furthermore, room temperature electroluminescence (EL) was achieved from nc-Si/SiC system and the possible mechanism of radiative recombination mechanism was discussed.

Germanium (Ge) has gained much interest due to the potential of becoming a direct band gap material and an efficient light source for the future complementary metal-oxide-semiconductor (CMOS) compatible photonic integrated circuits. In this paper, highly biaxial tensile strained Ge quantum wells (QWs) and quantum dots (QDs) grown by molecular beam epitaxy are presented. Through relaxed step-graded InGaAs buffer layers with a larger lattice constant, up to 2.3% tensile-strained Ge QWs as well as up to 2.46% tensile-strained Ge QDs are obtained. Characterizations show the good material quality as well as low threading dislocation density. A strong increase of photoluminescence (PL) with highly tensile strained Ge layers at low temperature suggests the existence of a direct band gap semiconductor.