Light Emission by Group Four Semiconductors in Vertical Optical Resonators
Published : 19 October 2020
Group Four (GF) semiconductors such as silicon, germanium and their alloys are the key materials of modern technologies for the electronic data processing. However, use of this class of materials for optoelectronic applications is hindered by the indirect nature of its band gap. The recent rise of direct band gap, group four alloys of the (Si, Ge, Sn) family has considerably renewed research around GF photonics since monolithic integration of an optical gain material on full Si wafers is now achievable in the frame of CMOS compatible processes. Our group has a strong expertise in the realization of infrared GeSn laser sources made from relatively thick GeSn layers in different cavities, including microdisks, photonic crystals, or corner cube cavities, with the demonstration for instance of a significant wavelength tunability and lasing close to room temperature , .
The work proposed here is experimental and has a twofold objective.
First, the choice of the optical cavity configuration can have a deep impact on the light-matter interaction and the lasing properties, can dictate the gain medium characteristics and directly affects the light out coupling efficiency. Turning from in plane to vertical cavities, in a configuration where horizontal top and bottom dielectric mirrors ensure optical feedback on the gain medium, opens new perspectives for the integration and the type of GeSn photon sources. The candidate will first design the optical stack and fabricate the overall cavity in clean rooms (Plateforme Technologique Amont), starting from our GeSn stacks on Si wafers and using conventional techniques of physical deposition, chip bonding and etching. Optical characterization by infra red reflectivity and photoluminescence will follow. Depending on the experiments progress, integration of our current pn junction stacks into the newly designed optical cavities could lead by the end of the internship to electrically driven vertical cavity light sources.
The second objective constitutes an exploratory groundwork aiming at modifying the dimensionality of the gain medium, switching from bulk GeSn layers on Ge to GeSn quantum dots on Si. Interest in reducing the dimensionality is in particular driven by the ability to grow GeSn on high electronic barrier materials, which is not easily achievable with the traditional bulk SiGeSn/GeSn system. Combined with the discretization of the electronic states in GeSn quantum dots, doing so could lead to optical emission in the telecom range, whereas bulk GeSn is known to emit in the 2-5 μm spectral interval, thereby greatly opening the application field of GF sources. The candidate will use our molecular beam epitaxy equipment for the growth and microscopy techniques to characterize the epilayers.
Merging the two above axes could be extended in a more in depth PhD work, with, among other possibilities, the first exploratory studies on the light emission properties of Group Four quantum dots inserted or not in a cavity. The candidate will have to work in close cooperation with the members of the SiNaPS laboratory (growth, optics, clean rooms). Skills in condensed matter physics together with appreciating the experimental work are expected.
 Q. M. Thai et al, Appl. Phys. Lett. 113, 051104 (2018)
 J. Chrétien et al, ACS Photonics, 2019, 6, 10, 2462–2469
Duration: 6 mounths
From 2021 Febuary 1st
Pheliqs –Quantum Physics and Engineering (CEA/IRIG/SPINTEC)
17 avenue des martyrs
38054 GRENOBLE cedex 9