Properties of InGaAs/InAlAs double quantum wells toward spin-filtering application

We recently determined the intrinsic constant for the Rashba effect in (001)InP-matched InGaAs/InAlAs quantum wells (QW) [1]. We now apply this knowledge to band-engineer a spin-filter based on the double QW (DQW) [2]. Firstly, we studied the subband energy spectra of the InGaAs/InAlAs DQW from the beatings in the Shubnikov de Haas (SdH) oscillations. The basic properties obtained here provide useful information to refine the device structures for the spin-filter devices based on the DQW system [2]. In our DQW samples, a thin barrier layer of In$_{0.52}$Al$_{0.48}$As ($d_{\rm B}=$ 1.5$\sim$5 nm) is sandwiched with non-doped QW layers of In$_{0.53}$Ga$_{0.47}$As ($d_{\rm QW}=$ 10 nm). By carefully tuning the doping densities above and below the DQW part and the top-gate voltage, the potential profile of this DQW should be ideally made symmetric about the middle barrier layer, though not yet realized in our experiment. The experimental results of our not-yet-ideal DQW samples showed clear beatings in the SdH data, which originate from both the subband and Rashba splittings. We report on our successful separation of these two effects based on the proper band-bending assumptions.\\[4pt] [1] Faniel, et.al., Phys. Rev. B {\bf 83}, 115309 (2011).\\[0pt] [2] Souma, et.al, arXiv:1304.6992.