The development of ultrahigh-quality-factor (Q) silicon-on-insulator (SOI) microring resonators based on silicon wire waveguides is presented. An analytical description is derived, illustrating that in addition to low propagation losses the critical coupling condition is essential for optimizing device characteristics. Propagation losses as low as 1.9 +/- 0.1 dB/cm in a curved waveguide with a bending radius of 20 microm and a Q factor as high as 139.000 +/- 6.000 are demonstrated. These are believed to be the highest values reported for a curved SOI waveguide device and for any directly structured semiconductor microring fabricated without additional melting-induced surface smoothing.

Recent research interests on the development of Si-based light emitting devices have been highly motivated by the demands of optical interconnects in the Si CMOS chip technology, in view of monolithic integration of optoelectronic devices on a Si chip to produce a new generation of high density high performance CMOS ICs with high reliability and low cost. As predicted in the SIA roadmap, accompanying with the fast reduction the device feature size, the maximum interconnect length will also increase from the present ∼2 km on a logic chip to ≥20 km in 10 years. The circuit performance of CMOS will then be limited by the bandwidth of conventional electronic interconnects. It is desirable to develop fully Si-based optical interconnects. However, a highly efficient Si light emitter is so far missing, due to the inherent indirect bandgap of Si. Many different approaches have been proposed and a lot of effort has been made during the past few years. Er-doping in Si has attracted some special interest [1] due to observations of intense and sharp electroluminescence (EL) at the interesting wavelength of 1.54 μm at room temperature from structures containing layers that are doped with Er to concentrations of 0.1-2x1020 cm-3 made by either low-temperature ion implantation followed by a solid phase epitaxy process, [2] or molecular beam epitaxy (MBE). [4]. Er-doped light emitting devices have several advantages in optical interconnect applications. The transition, which emits the light, is between atomic levels, so that the same output wavelength can be obtained from device to device and from wafer to wafer. Furthermore, it does not depend on the heat-sink temperature, which is a usual problem with light emission via band-to-band recombination in semiconductor homo- or hetero-structures. There are several other important issues regarding output power and modulation frequency of Er-doped light emitting sources, in particular, how the Er-ions are optically activated and being effectively pumped to obtain an optical gain. Since a long spontaneous decay time of Er emission limits Er- doped LEDs to be used as a power efficient device at high modulation frequency, to achieve stimulated emission is thus a key to making Er-doped Si materials and devices feasible for the use of optical interconnects.

We report on improved filter characteristics of microring resonators (MRs) used as add-drop multiplexer for integrated photonic circuits. By introducing an asymmetrical coupling of the signal waveguides; to the resonator, a higher throughput attenuation And drop efficiency is Attained. The throughput attenuation is the decisive property for the application of microrings in photonic networks since it determines the crosstalk between drop signal and add signal at the throughput channel of an add-drop multiplexer. Experimental, results are compared with analytical relations. MRs with a free-spectral range of 24 nm are fabricated on silicon-on-insulator substrates. A crosstalk reduction by 8.8 dB due to asymmetrical coupling is demonstrated.

We studied the vertical correlation of small hut-like Ge islands in Si–Ge multilayers grown by molecular beam epitaxy (MBE) at 510°C in the modified Stranski–Krastanov growth mode. The fundamental, structural and optical properties of stacked Ge islands embedded in Si are analyzed by in-situ RHEED, TEM, photoluminescence (PL), and photocurrent (PC) spectroscopy. Ge islands of about 20 nm width and 2 nm height reveal a reduction in the critical Ge coverage for correlated growth for Si spacer widths below about 14 nm. This value is much smaller than observed for dome-like islands of about 80 nm size deposited at higher temperatures. Such a scaling of island separation for stacked growth with island diameter is suggested by finite element simulations of elastic strain relaxation in islands. The correlation affects island size, island density, and local strain fields which may have a direct impact on band offsets and the electronic coupling of stacked islands. This is important for possible application in devices like NIR Si–Ge dot photodetectors and tunneling structures.

In this letter, we report on the influence of the space charge region width in erbium- and oxygen-doped silicon light-emitting diodes on the electroluminescence (EL) power at 1.54 μm under reverse bias conditions. The space charge region width was varied by codoping the Si:Er:O layer with boron, thereby compensating the Er–O donors. We observe a strong enhancement of the EL power with increasing width. The data indicate the existence of a dark region of approximately 45 nm in the pn junction, in which no light is generated due to a lack of hot carriers which are necessary for impact excitation of Er3+ ions.