L. Ding

Laterally-current-injected light-emitting diodes based on nanocrystalline-Si/SiO 2 superlattice

Laterally electrically-pumped Si light-emitting diodes (LEDs) based on truncated nanocrystalline-Si (nc-Si)/SiO2 quantum wells are fabricated with complementary-metal-semiconductor-oxide (CMOS) process. Visible electroluminescence (EL) can be observed under a reverse bias larger than ~6 V. The light emission would probably originate from the spontaneous hot-carrier relaxations within the conduction and the valance bands when the device is sufficiently reverse-biased. The EL spectral profile is found to be modulated by varying structure parameters of the interdigitated finger electrodes. Up to ~20 times EL intensity enhancement is achieved as compared to vertical-current-injection LED prepared using the same material system. Based on the lateral-current-injection scheme, a Si/SiO2 MQW LED with Fabry-Perot (FP) microcavity and an on-chip waveguided LED that emits at 1.55-µm are proposed.

Ge waveguide photodetectors with responsivity roll-off beyond 1620 nm using localized stressor

We report a novel Ge waveguide photodetector and the fabrication on silicon-on-insulator (SOI) platform. Localized stressor structures were incorporated to tune the responsivity roll-off wavelength. With the localized stressor structure, the roll-off in responsivity is found to be red-shifted from 1520 nm to beyond 1620 nm, i.e., a flat responsivity over the entire C- and L-band is obtained. This technique makes Ge a promising material for fabricating monolithic high-responsivity receivers covering the entire C- and L-band fiber optic communications.

Dependences of photoluminescence from P-implanted epitaxial Ge

A systematic investigation has been carried out to study the influence of various annealings and implantations on the photoluminescence (PL) properties of phosphorus (P)-implanted Ge epitaxial films on Si substrate. For un-capped Ge samples, rapid thermal annealing (RTA) at 700 °C for 300 seconds yields the strongest PL emission peaked at 1550 nm. The influence of employing various capping layers (i.e., SiO(2), Si(3)N(4), and α-Si ) on the PL properties has been investigated. The capping layers are found to effectively decrease the dopant loss, leading to a significant PL enhancement. Si(3)N(4) is found to be the most efficient capping layer to prevent dopant out-diffusion and thus lead to strongest PL. Furthermore, it has been found that capping layers not only enhance the PL intensities but also make PL emission peak red- and blue- shift, depending on the stress type of the capping films. The effect of implantation dose on the PL has been also investigated.

Electroluminescence from amorphous-SiNx:H/SiO2 multilayers using lateral carrier injection

We report the observation of photoluminescence and electroluminescence from amorphous-SiNx:H/SiO2 multilayer structures. An effective method of current injection has been implemented for electrical excitation of these structures whereby the electric field is applied parallel to the plane of the multilayers. Compared to conventional electrical injection with current flowing normal to the plane of multilayers, this method has greatly improved the current density. Such structures are promising candidate as Si based light source for Si optoelectronics technology.

Slope efficiency and spurious-free dynamic range of silicon Mach-Zehnder modulator upon carrier depletion and injection effects

We investigate the performances of a silicon PN-junction Mach-Zehnder modulator for analog application. The slope efficiency and spurious-free dynamic range (SFDR) of such a modulator upon carrier depletion and carrier injection effects are characterized and compared. Input RF frequency-dependence measurements show that the depletion-type modulator is usually with ~20 dB ∙ Hz(2/3) higher SFDR comparing to the injection-type modulator, yet with an order-of-magnitude lower slope efficiency. For the depletion-type and injection-type modulators, the measured maximum SFDRs are respectively ~95 dB ∙ Hz(2/3) and 75 dB∙Hz(2/3), with maximum slope efficiency of 0.3 V(-1) and 8 V(-1<). We numerically model the SFDR by using the experimentally extracted effective refractive index change, which shows good agreement with the measurements.

Light emission of 2D photonic crystal based on nanocrystal-Si/SiO2 superlattice structure

Because of the its indirect bandgap structure, it is a huge challenge to establish an efficient Si light emitting diode (LED) compatible with complementary metal-oxide-semiconductor (CMOS) process. In this paper, we provide an alternative route to overcome this difficulty based on the unique property of photonic crystals (PhC). A vertical-current-injection LED based on three-dimensional-confined structures with triangular-lattice air-hole PhC patterns has been fabricated with enhanced light extraction from the active region (i.e., silicon-rich-oxide/SiO2 multilayer stack). The intensity and profile of photoluminescence (PL) and electroluminescence (EL) has been found to be efficiently modulated by controlling the optical modes of the periodic arrays via varying their structural parameters. It provides a convenient way of redistributing the light energy in desired form and orientation. With optimized lattice constant/radius ratio, significant enhancement up to ~7 times in both PL and EL emissions can be obtained. The mechanisms for different enhancement features have also been theoretically analyzed based on coherent scattering and quantum electrodynamics effects, which is well consistent with the experiment observation.

High speed energy-efficient germanium electro-absorption modulator featuring monolithic integration with germanium p-i-n photodetector

We report a novel evanescent-coupled germanium electro-absorption modulator with a small active area of 16 µm2 giving an extinction ratio of ∼ dB for a wavelength range of 1580–1610 nm. In addition, monolithic integration of both evanescent-coupled Ge electro-absorption modulator and Ge p-i-n photodetector is demonstrated for the first time.

Photon detection and emission of epitaxial Ge on Si with potential applications in microwave photonic filters

Microwave photonic filter requires high-speed Radio frequency (RF)-optical and optical-RF signal conversion. Light sources and photo-detectors (PDs) are indispensible for such conversions. Monolithic integration of functions of photon emission and detection is demonstrated using epitaxial Ge on Si. The fabricated waveguided PD shows a high bandwidth of 10 GHz with the responsivity of 0.8 A/W and dark current of 150 nA at −1V. The photoluminescence (PL) properties of P-implanted Ge are studied, and an improved annealing process is demonstrated to enhance the light emission by 1 order. Electroluminescence (EL) is obtained from the waveguided n+-Ge light-emitting diode (LED), and the emitted power has been studied as a function of injected current. The successful demonstration of both waveguided PD and LED on single Si chip would be attractive for fabricating a compact size microwave photonic filter with low cost and high integrity.

Silicon waveguide based splitter

A silicon waveguide based splitter is a key device for polarization diversity circuit. A bilayer waveguide structure was proposed by MIT to split the input light into its orthogonal components. It is challenging to fabricate a bilayer silicon waveguide by the conventional two-step-etching process due to precise alignment and accurate etch thickness required. In addition, the partial etched waveguide would introduce additional insertion loss due to its non-perfect surface. Here we propose a novel method to fabricate splitters with various dimensions by using selective silicon epitaxial growth to achieve bilayer structure. The performance of the splitter fabricated is evaluated through Finite-difference-time-domain simulations. The insertion loss and efficiency of the splitters obtained is experimentally investigated. The proposed approach is potentially useful for integrated photonic circuit consisting of passive waveguides and active photodetector devices.

Low-voltage high-efficiency light emitting diodes with lateral-current injection based on truncated Si/SiO2 quantum wells

An efficient low-voltage lateral current-injection CMOS-compatible light emitting diode (LED) based on Si/SiO2 multiple quantum wells (MQW) is reported. This is the first time that a lateral current-injection LED is demonstrated with Si/SiO2 MQW structures. Strong electroluminescence (EL) in the wavelength ranging from 450 to 850 nm can be observed when the device is reverse-biased at the voltage of as low as ~6 V with the current of ~1 mA. With the lateral current injection structure, the working voltage of the LED is significantly reduced because the voltage is fully applied across the active region instead of dielectrics which cannot be avoided in vertical current-injection Si/SiO2 quantum well LEDs that have received intensive research attention during the last decade. The external quantum efficiency is ~20 times higher than that of the conventional vertical current-injection LEDs based on Si/SiO2 MQW. The light emission would probably originate from the impact ionization due to the hot carriers generated in ultra-thin Si film when the device is reverse-biased. The lateral configuration provides a versatile technology platform, since many light-extraction and mono-chromaticity enhancement techniques can be directly applied onto the top emission window.