Spin-controlled switching of lasing circular polarizations in (HO)-oriented VCSELs

摘要

We discuss high speed switching of lasing circular polarizations in VCSELs by optical spin injection. We conducted polarization- and time-resolved measurements of two consecutive lasing outputs from a (110)-InGaAs/GaAs VCSEL at 77 K with different time delays between the two optical excitations for alternately up- and down-spin electrons. 1-GHz switching of lasing circular polarizations has been demonstrated with taking advantage of the long electron spin relaxation time ts in (HO)-QWs. Rate equation analysis closely reproduced the measured results and showed that shortening the carrier lifetime tc while preserving the long ts is a straightforward solution for faster switching since the residual unpolarized electrons limit the switching speed. Thus, we dry-etched the (HO)-QWs into micro-posts to introduce the surface non-radiative recombination using ECR-RIE, and investigated the rc and rs. Spin-polarized carriers were optically excited in square posts with different sizes from 0.5 urn to 30 um, and the time evolutions of two orthogonal circular polarization components of photoluminescence were measured by a streak camera. The long rs (~1.3 ns) in the (HO)-QW wafer is found to be preserved even when the sidewall boundaries with fast surface recombination are introduced and the tc is drastically shortened. The same rate equation analysis indicated that spin-controlled VCSELs with such (HO)-QW micro-posts will exhibit faster switching thanks to the shortened tc and preserved long rs. In particular, 20-GHz switching is expected with 0.5-(im posts, although the threshold pulse energy per unit area becomes 2.9 times larger than that for 1-GHz switching without post structure.