Highly n-doped germanium-on-insulator microdisks with circular Bragg gratings.

We demonstrate germanium (Ge) microdisks surrounded by highly reflective circular Bragg gratings on highly n-doped germanium-on-insulator (GOI) substrate. The GOI substrate is fabricated by wafer bonding from Ge grown on Si substrate, and n-type doping concentration of 2.1×1019 cm-3 is achieved by phosphorus diffusion from a spin-on-dopant source. Very sharp Fabry-Perot resonant peaks with high contrast fringes and Q-factors up to 400 are observed near the direct band gap of Ge in photoluminescence spectra. The reflectivity of gratings are enhanced by a factor larger than 3 in a wide wavelength range from 1.57 to 1.82 µm, compared with that of Ge/SiO2 interfaces in normal microdisks without circular Bragg gratings. The surface emission intensity of the devices is found to be increased by the grating period. Our results indicate that GOI microdisk with circular Bragg grating is a promising optical resonator structure suitable for realizing low threshold, compact Ge lasers integrated on Si substrate.

Waveguide-integrated microdisk light-emitting diode and photodetector based on Ge quantum dots.

Microdisk integrated with a bus waveguide is fabricated on silicon-on-insulator substrate containing Ge self-assembled quantum dots as active medium. The device is demonstrated to be operated as both light-emitting diode and photodetector. At forward bias, carriers are injected into the microdisk and light emission at 1.45-1.6 µm is extracted through the waveguide via microdisk-waveguide coupling. Sharp resonant peaks with Q-factor as high as 1350 are obtained in the electroluminescence spectra, corresponding to whispering gallery modes of the microdisk. At reverse bias, the device functions as a resonant cavity enhanced photodetector with wavelength-selective photo-response. The photo-current at resonant wavelength of 1533.65 nm is 50 times larger than that at non-resonant wavelength. The dark current density of the photodetector is as low as 0.29 mA/cm2 up to -10 V bias and the peak responsivity is 5.645 mA/W.

Silicon-based current-injected light emitting diodes with Ge self-assembled quantum dots embedded in photonic crystal nanocavities.

Room temperature light emission from Ge self-assembled quantum dots (QDs) embedded in L3-type photonic crystal (PhC) nanocavity is successfully demonstrated under current injection through a lateral PIN diode structure. The Ge QDs are grown on silicon-on-insulator (SOI) wafer by solid-source molecular beam epitaxy (SS-MBE), and the PIN diode is fabricated by selective ion implantation around the PhC cavity. Under an injected current larger than 0.5 mA, strong resonant electroluminescence (EL) around 1.3-1.5 µm wavelength corresponding to the PhC cavity modes is observed. A sharp peak with a quality factor up to 260 is obtained in the EL spectrum. These results show a possible way to realize practical silicon-based light emitting devices.

Room-temperature electroluminescence from Si microdisks with Ge quantum dots.

A current-injected silicon-based light-emitting device was fabricated on silicon-on-insulator (SOI) by embedding Ge self-assembled quantum dots into a silicon microdisk resonator with p-i-n junction for current-injection. Room-temperature resonant electroluminescence (EL) from Ge self-assembled quantum dots in the microdisk was successfully observed under current injection, and observed EL peaks corresponding to the whispering gallery modes (WGMs) supported by the microdisk resonator were well identified by means of numerical simulations.