Magnetic field effect on the lasing behavior of GaAs nanowires on iron*

We investigated the effect of a magnetic field on the lasing behavior of GaAs nanowires (NWs) on an iron film. The conical GaAs NWs with an acceptor concentration of 2 x 10¹⁹ cm^-3 were coated with an 8 nm thick Al₂O₃ layer to reduce band bending. The NWs on iron film were excited with ultra-short 150 fs pulses from Ti: Sapphire laser tuned to 720 nm at a cryostat temperature of 77 K. A permanent magnet was integrated into the cryostat system allowing to apply a magnetic field of ~0.3 T in Faraday and Voigt configuration with respect to the long axis of the NWs. Scanning microscope images reveal average dimensions of the lasing NWs to be ~ 3.3 μm long with a tip diameter of ~ 370 nm and a base diameter of ~ 530 nm. The NWs show an onset of lasing at ~40 mW without magnet field. Finite-difference time-domain simulations show that a predominantly photonic mode with moderate plasmonic losses of ~ 3000 cm^-1, is responsible for lasing. While the lasing behavior was not noticeably influenced by a magnetic field in Faraday configuration the threshold power was significantly increased in Voigt configuration. The reduced NW laser intensity in Voigt configuration suggests a magnetic field induced spatial charge separation of the e-h pairs.