Edge-emitting electrically pumped room-temperature spin laser

• Applicants: Professor Dr. Martin Hofmann; Professor Dr. Heiko Wende; Professor Dr. Andreas Dirk Wieck
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392782903

Our goal is to realise the first electrically pumped room temperature spin diode lasers in the world, which can operate without external magnetic field. By spin injection we aim to achieve a circular polarization degree above 30%. Our concept for that purpose is based on an edge emitting diode laser with bulk active region. This is necessary in order to achieve a polarization insensitive optical gain which then can be intentionally modified by spin injection from ferromagnetic contacts in remanence. The optical gain in the actually commercially used quantum well lasers is polarisation dependent, and therefore such devices are not suited for our project. In vertical cavity surface emitting lasers (VCSELs), which are typically the basis for spin-laser concepts, the transport paths of the injected carriers are typically in the range of several µm and therefore much longer than the spin relaxation length which we found to be only about 25nm. Much shorter injection lengths (path of the carriers from injection contact to active region) can potentially be achieved in edge emitting laser diodes. This edge emitting device geometry in combination with an active region that provides polarization insensitive optical gain, is therefore chosen for this project in order to demonstrate electrical spin injection at room temperature. The expertises of the participating groups are perfectly complementary for this project. The sub-tasks are as follows: Group Hofmann elaborates the structure design (architecture of active region, injector) in close collaboration with the other partners. The group also does part of the processing and the final optical characterisation. Group Wieck does the semiconductor growth, parts of the processing, and the transport characterisation. Group Wende deposits the ferromagnetic n-contacts (e.g. Fe- or Fe3Si-layers) with MgO-tunnel barriers. These magnetic contacts will be analysed at synchrotron sources via x-ray absorption spectroscopy and x-ray circular dichroism, and in the own laboratory via Mössbauer spectroscopy (CEMS). In further steps, the laser devices will be processed for the final characterisation by plasma etching of the contacts and bonding in collaboration of the groups Hofmann and Wieck. Within this final optical characterisation, we aim to prove the control of the optical output polarisation by the injected spins and we want to analyse which potential advantages a spin-controlled laser may have in comparison with a conventional laser. For that purpose, the dynamics of the polarisation switching via spin injection will be characterized with emphasis to the contrast between the different polarization states and the temporal switching dynamics. The interpretation of these measurements will be supported by polarization sensitive measurements of the optical gain upon spin injection.

• DFG Programme: Research Grants