Edward T. Fei

Low-voltage broad-band electroabsorption from thin Ge/SiGe quantum wells epitaxially grown on silicon.

We demonstrate electroabsorption contrast greater than 5 dB over the entire telecommunication S- and C-bands with only 1V drive using a new Ge/SiGe QW epitaxy design approach; further, this is demonstrated with the thinnest Ge/SiGe epitaxy to date, using a virtual substrate only 320-nm-thick. We use an eigenmode expansion method to model the optical coupling between SOI waveguides and both vertically and butt-coupled Ge/SiGe devices, and show that this reduction in thickness is expected to lead to a significant improvement in the insertion loss of waveguide-integrated devices.

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.

Microring bio-chemical sensor with integrated low dark current Ge photodetector

An integrated Ge photodetector of very low dark current density is demonstrated in an optoelectronic integrated circuit label-free biosensing system. The sensor system consists of a microring for optical sensing and a monolithically integrated Ge detector. For point-of-care applications, integration of Ge detector increases the reliability of measurement by eliminating mechanical-optical alignment of output signals. Optimizing Ge detector performance will further enhance system signal-noise ratio and reliability. For homogeneous sensing, the system has a sensitivity of ∼18.8 nm/RIU and a detection limit of 3.50 × 10−5.

Investigation of germanium quantum-well light sources.

In this paper, we report a broad investigation of the optical properties of germanium (Ge) quantum-well devices. Our simulations show a significant increase of carrier density in the Ge quantum wells. Photoluminescence (PL) measurements show the enhanced direct-bandgap radiative recombination rates due to the carrier density increase in the Ge quantum wells. Electroluminescence (EL) measurements show the temperature-dependent properties of our Ge quantum-well devices, which are in good agreement with our theoretical models. We also demonstrate the PL measurements of Ge quantum-well microdisks using tapered-fiber collection method and quantify the optical loss of the Ge quantum-well structure from the measured PL spectra for the first time.

Selective area growth of germanium and germanium/silicon-germanium quantum wells in silicon waveguides for on-chip optical interconnect applications

We propose a robust fabrication process for growing Ge and Ge-based heterostructures in growth windows with Si sidewalls which can be applied to growth in thick Si optical waveguides. Sidewall growth is eliminated by the presence of a dielectric spacer layer which covers the sidewalls. We demonstrate the effectiveness of this process by selective-area growth of Ge and Ge/SiGe quantum wells, and show an improved performance and increased process reliability over previous work.

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.

Room Temperature Photoluminescence from Ge/SiGe Quantum Well Structure in Microdisk Resonator

In this paper, we report the enhanced direct band gap photoluminescence from carrier confinement in Ge quantum wells with SiGe barriers at room temperature. We have also fabricated a microdisk resonator and present the tapered-fiber coupled high-Q cavity mode from Ge quantum wells.

Tensile-strained Ge/SiGe multiple quantum well microdisks

An efficient monolithically integrated laser on Si remains the missing component to enable Si photonics. We discuss the design and fabrication of suspended and tensile-strained Ge/SiGe multiple quantum well microdisk resonators on Si for laser applications in Si photonics using an all-around SiNx stressor. An etch-stop technique in the Ge/SiGe system is demonstrated and allows the capability of removing the defective buffer layer as well as providing precise thickness control of the resonators. Photoluminescence and Raman spectroscopy indicate that we have achieved a biaxial tensile strain shift as high as 0.88% in the microdisk resonators by adding a high-stress SiNx layer. Optical gain calculations show that high positive net gain can be achieved in Ge quantum wells with 1% external biaxial tensile strain.

Tensile-strained Ge/SiGe quantum-well microdisks with overlying SiN x stressors

We demonstrate Ge/SiGe multiple-quantum-well microdisks on Si substrates with SiNx stressors on top. The strain transferred from the SiNx to the Ge quantum wells are determined by photoluminescence and Raman measurements, and are in agreement with simulation results.