Kevin M. Chen

High-quality Ge epilayers on Si with low threading-dislocation densities

High-quality Ge epilayers on Si with low threading-dislocation densities were achieved by a two-step ultrahigh vacuum/chemical-vapor-deposition process followed by cyclic thermal annealing. On large Si wafers, Ge on Si with threading-dislocation density of 2.3×107 cm−2 was obtained. Combining selective area growth with cyclic thermal annealing produced an average threading-dislocation density of 2.3×106 cm−2.We also demonstrated small mesas of Ge on Si with no threading dislocations. The process described in this letter for making high-quality Ge on Si is uncomplicated and can be easily integrated with standard Si processes.

SiO2/TiO2 omnidirectional reflector and microcavity resonator via the sol-gel method

Thin films of SiO2 and TiO2 were used to fabricate one-dimensional photonic crystal devices using the sol-gel method: an omnidirectional reflector and microcavity resonator. The reflector consisted of six SiO2/TiO2 bilayers, designed with a stopband in the near infrared. Reflectivity over an incident angle range of 0°–80° showed an omnidirectional band of 70 nm, which agrees with theoretical predictions for this materials system. The microcavity resonator consisted of a TiO2 Fabry–Perot cavity sandwiched between two SiO2/TiO2 mirrors of three bilayers each. We have fabricated a microcavity with resonance at λ=1500 nm and achieved a quality factor of Q=35. We measured a resonance frequency modulation with a change in incident angle of light and defect layer thickness.

Data management in the CarTel mobile sensor computing system

We propose a reusable data management system, called CarTel, for querying and collecting data from intermittently connected devices. CarTel provides a simple, incrementally-deployable platform for developing automobile-based sensor applications. Our platform provides a dynamic query system that allows both continuous (standing) and one-shot geo-spatial queries over car position, speed, and sensory data as well as a both a low-cost/high-bandwidth substrate for communicating with a large network of mobile devices.

Erbium in Si-based light confining structures

Abstract Erbium can provide the Silicon with optoelectronic capabilities. Er:Si has a very sharp emission line at 1.54 μm. The main limitation of Erbium is its low emission efficiency at room temperature. In this work, we show that microcavities can modify the optical properties of the Erbium. Two different mechanisms for modifying the optical properties of the Er ions were studied, one in which the collection of light is optimized. In this case, an enhancement of the photoluminescence by a factor of 1000 was obtained. The second mechanism that was studied is a strong photon-Erbium interaction. In this case, we show evidence for mixing of optical properties of Erbium and photons indicating that properties such as lifetime and energy levels can be changed externally.

Growth, crystallization, and room temperature photoluminescence of Er2O3 thin films

Room temperature photoluminescence (RT PL) has been obtained from Er2O3 thin films fabricated via reactive sputtering of Er metal in Ar/O2 and subsequently annealed. Upon annealing, the PL spectra develop maxima at 1549 nm and 1541 nm for films treated at 650 degrees C and 1020 degrees C, respectively. Crystallization at high temperature results in RT PL and a lifetime of approximately 10 ms at 4K.