Session Chair: Jun-Wei Luo, Institute of Semiconductors, Chinese Academy of Sciences
10:30am - 11:00am Invited
Lasing from SiGeSn/GeSn Structures: Films, Double Heterostructures and Multiple Quantum Wells
Detlev GRÜTZMACHER1, Dan BUCA1, Daniela STANGE1, Nils VON DEN DRIESCH1, Francesco ARMAND PILON2, Thomas ZABEL2, Hans SIGG2
1Peter Grünberg Institut and JARA-FIT, Forschungszentrum Jülich, Germany; 2Laboratory for Micro- and Nanotechnology, Paul Scherrer Institute, Switzerland
The group IV alloy GeSn provide a direct band gap for Sn concentration above ~8%, which is far beyond the solid solubility limit of ~1%. Recently high quality GeSn alloys with Sn concentrations up to 14.5% could be grown at low temperatures and high growth rates by means reactive gas source epitaxy. These GeSn have a direct band gap, in the range of 0.48-0.63 eV dependening on the Sn concentration. Thus these materials pave the road for the integration of optoelectronic circuitry on Si (100) substrates.
Optically pumped laser in the Fabry Perot geometry as well as microdisc lasers have been fabricated from GeSn films, SiGeSn double heterostructures and SiGeSn/GeSn multiple quantum wells (MQW) on Ge virtual substrates. Comparing laser fabricated from thick GeSn films to MQW structures, the threshold required to achieve lasing dropped drastically and the emission efficiency increased. This can be attributed to reduced optical losses due to surface scattering as well as due to the reduced number of states in the multiple quantum wells, which allows carrier inversion at smaller pumping powers. However, due to the very small effective mass of electrons in the Г valley compared to large mass in the L valley, the quantum wells have to be designed carefully. For thin quantum wells the confinement shift of the subbands of the Г valley is larger than that for the L valley reducing the directness and may even turn it into an indirect material.
To achieve electrically pumped lasing double hetero- and MQW-structures have been grown using SiGeSn cladding and barrier layers. The SiGeSn cladding layers have been partially doped to achieve p-i-n junctions. First devices have been fabricated showing a superior electroluminescence efficiency of MQW structures.
1University of Southampton, United Kingdom; 2Hitachi, Japan; 3University of Tokyo, Japan
Germanium (Ge) is a group-IV semiconductor promissing for both advanced electronics and photonics applications integrated on Silicon (Si) chips. The high electron mobility is favourable for the Complementary Metal-Oxide-Semiconductor (CMOS) transistors, while the quasi-indirect band gap character is useful for developing light sources for Si photonics. In this talk, we will review the current developments of Ge light sources fabricated using nano-fabrication technologies compatible with CMOS processes. In particular, we review recent progress in applying high-tensile strain to Ge to reduce the direct band gap. By making a freestanding beam using Micro-Electro-Mechanical-Systems (MEMS) processes, extremely high-tensile strain exceeding a few % can be applicable to Ge, converting indirect to direct band gap characters. Another important process is doping Ge with donor impurities to fill the indirect band gap valleys in the conduction band. Realization of carrier confinement structures and suitable optical cavities will also be discussed. Finally, we will discuss various applications of Ge light sources in potential photonics-electronics convergent systems.
11:30am - 12:00pm Invited
Strained Ge Nanowire with High-Q Optical Cavity for On-Chip Light Sources
Inha University, South Korea
Photonic-integrated circuits hold the key to the ultimate miniaturization of various disruptive technologies such as LiDAR for autonomous vehicles, bio-chemical sensors and optical interconnects. However, the realization of fully functional photonic-integrated circuits is currently limited by the absence of an efficient light source on silicon. In this talk, we present an infrared light emission from highly strained germanium coupled with high-Q nanophotonic cavity. Our design encompasses all the aspects of potential low-threshold lasers: highly strained germanium gain medium, strain-induced pseudoheterostructure, and high-Q nanophotonic cavity. A simple method to change the level of strain in the light-emitting medium allows us to tune the emission wavelength over more than 400 nm. Our demonstration of wavelength-tunable Ge light emitters paves the way towards a practical on-chip light source for photonic-integrated circuits.