Injection and control of spin-polarized electrons into highly uniform semiconductor quantum dots

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1.Uniform self-formation of InAs/GaAs and GaSb/GaAs quantum dotsA self size-limiting effect of InAs quantum dots was observed and provided the highly uniform formation of the InAs quantum dots, which revealed a narrow photoluminescence linewidth of 17 meV. The uniform formation of the GaSb quantum dots was attempted by using the appropriate growth conditions enhancing the surface migration. As the result, a narrow photoluminescence linewidth of 49 meV was obtained successfully.2.Stacking growth of InAs quantum dots and self-formation of GaAs nanoholesThe stacking growth of the uniform InAs quantum dots was attempted, and, influences of the strain field on the stacking growth were studied. From these results, the stacked quantum-dot structure was controlled precisely, and, the uniform stacking growth technique was developed. The uniformly stacked InAs quantum dots revealed a narrow photoluminescence of 17 meV. Next, the GaAs nano-holes were spontaneously formed just above the embedded InAs quantum dots by the annealing after the GaAs capping growth. The quantum-dot diodes with the nano-contacting InAs dots through the GaAs nano-holes were proposed and were fabricated. The local tunnel injection of electrons was confirmed successfully.3.Evaluations of spin physics in semiconductor quantum dotsThe high dot density of the InAs quantum dots was achieved by using a new method introducing the GaSb/GaAs buffer layers. The spin polarization of the high-density quantum dots was evaluated by the polarized photoluminescence measurement and decreased with increasing the dot density. Next, the spin-polarized scanning tunneling microscopy using the optically pumped GaAs tips and the magnetic tips was attempted. In case of the Ni thin-film sample, spin-dependent tunneling current was detected. These techniques have an attractive potential for studying the spin physics in the semiconductor quantum dots.