Yiwen Rong

Strong enhancement of direct transition photoluminescence with highly tensile-strained Ge grown by molecular beam epitaxy

Highly tensile-strained layers of Ge were grown via molecular beam epitaxy using step-graded InxGa1−xAs buffer layers on (100) GaAs. These layers have biaxial tensile-strain of up to 2.33%, have surface roughness of <1.1 nm, and are of high quality as seen with transmission electron microscopy. Low-temperature photoluminescence (PL) suggests the existence of direct-bandgap Ge when the strain is greater than 1.7%, and we see a greater than 100× increase in the PL intensity of the direct transition with 2.33% tensile-strain over the unstrained case. These results show promise for the use of tensile-strained Ge in optoelectronics monolithically integrated on Si.

Ge/SiGe Quantum Well Waveguide Modulator Monolithically Integrated With SOI Waveguides

We present a Ge/SiGe quantum well QCSE waveguide modulator that is monolithically integrated with SOI waveguides. The integrated device shows 3.2 dB contrast ratio with 1 V swing at 7.0 Gbps.

Quantum-Confined Stark Effect in Ge/SiGe Quantum Wells on Si

In this paper, we present observations of quantum confinement and quantum-confined Stark effect electroabsorption in Ge quantum wells 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 quantum well structures at similar wavelengths. We also designed and fabricated a coplanar high-speed modulator, and demonstrated modulation at 10 GHz and a 3.125-GHz eye diagram for 30-¿m-sized modulators.

Selective epitaxial growth of Ge/Si0.15Ge0.85 quantum wells on Si substrate using reduced pressure chemical vapor deposition

We investigate the selective epitaxial growth of Ge/Si0.15Ge0.85 quantum wells on prepatterned silicon substrates by reduced pressure chemical vapor deposition. A vertical p-i-n Si0.1Ge0.9 diode with Ge/Si0.15Ge0.85 quantum wells in the intrinsic region is selectively grown in holes in a SiO2 mask. We find perfect growth selectivity and very low dependence on size or arrangement of the mask holes. The fabricated p-i-n diode shows very low reverse leakage current and high breakdown voltage, suggesting good epitaxy quality. The quantum-confined Stark effect in this quantum-well system is observed for wavelengths >1.5 μm at room temperature.

Simple Electroabsorption Calculator for Designing 1310 nm and 1550 nm Modulators Using Germanium Quantum Wells

With germanium showing significant promise in the design of electroabsorption modulators for full complementary metal oxide semiconductor integration, we present a simple electroabsorption calculator for Ge/SiGe quantum wells. To simulate the quantum-confined Stark effect electroabsorption profile, this simple quantum well electroabsorption calculator (SQWEAC) uses the tunneling resonance method, 2-D Sommerfeld enhancement, the variational method and an indirect absorption model. SQWEAC simulations are compared with experimental data to validate the model before presenting optoelectronic modulator designs for the important communication bands of 1310 nm and 1550 nm. These designs predict operation with very low energy per bit ( <; 30×fJ/bit).

Ge/SiGe asymmetric Fabry-Perot quantum well electroabsorption modulators

We demonstrate vertical-incidence electroabsorption modulators for free-space optical interconnects. The devices operate via the quantum-confined Stark effect in Ge/SiGe quantum wells grown on silicon substrates by reduced pressure chemical vapor deposition. The strong electroabsorption contrast enables use of a moderate-Q asymmetric Fabry-Perot resonant cavity, formed using a film transfer process, which allows for operation over a wide optical bandwidth without thermal tuning. Extinction ratios of 3.4 dB and 2.5 dB are obtained for 3 V and 1.5 V drive swings, respectively, with insertion loss less than 4.5 dB. For 60 ?m diameter devices, large signal modulation is demonstrated at 2 Gbps, and a 3 dB modulation bandwidth of 3.5 GHz is observed. These devices show promise for high-speed, low-energy operation given further miniaturization.

A Ge/SiGe quantum well waveguide modulator monolithically integrated with SOI waveguides

We report a Ge/SiGe quantum well waveguide electroabsorption modulator that is monolithically integrated with silicon-on-insulator waveguides. The active quantum well section is selectively grown on a silicon-on-insulator substrate and has a footprint of 8 . The integrated device demonstrates more than 3.2-dB contrast ratio with 1-V direct voltage swing at 3.5 GHz. We also show the potential of this device to operate in the telecommunication C-band at room temperature.

Surface-Normal Ge/SiGe Asymmetric Fabry–Perot Optical Modulators Fabricated on Silicon Substrates

We demonstrate the first vertical-incidence Ge/SiGe quantum well reflection modulators fabricated entirely on standard silicon substrates. These modulators could help enable massively parallel, free-space optical interconnects to silicon chips. An asymmetric Fabry-Perot resonant cavity is formed around the quantum well region by alkaline etching the backside of the Si substrate to leave suspended SiGe membranes, upon which high-index-contrast Bragg mirrors are deposited. Electroabsorption and electrorefraction both contribute to the reflectance modulation. The devices exhibit greater than 10 dB extinction ratio with low insertion loss of 1.3 dB. High-speed modulation with a 3 dB bandwidth of 4 GHz is demonstrated. The moderate-Q cavity (Q ~ 600) yields an operating bandwidth of more than 1 nm and permits operation without active thermal stabilization.

Si-Ge surface-normal asymmetric Fabry-Perot quantum-confined stark effect electroabsorption modulator

The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMOS-compatible integrated optical modulators. Using an asymmetric Fabry-Perot design, we demonstrate the first surface-normal semiconductor modulator structure grown on silicon.

Ge quantum well resonator modulators

The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMOS-compatible integrated optical modulators. We demonstrate surface-normal asymmetric Fabry-Perot and microdisk resonator modulators employing Ge quantum wells grown on silicon.