Extremely high-density doping of magnetic impurity in magnetic semiconductors and surface nano-structure preparation by controlling fundamental surface process during MBE growth

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We have explored preparation process and materials properties of nanostructures consisted of semiconductors and magnetic materials in order to develop novel spin-electronics materials and devices. Major results obtained are as follows.(1)We have investigated reentrant behavior of RHEED intensity oscillation during low temperature MBE growth of GaAs on GaAs (001) c (4×4) surface,s and found that the origin is due to anomalous surface roughening, which takes place at very early stage of the growth at a substiate temperature of 400℃.(2)We have explored GaAs (001) c (4×4) α and c (4×4) β reconstructions by using scanning tunneling microscopy and I FED-IV technique, and determined their detailed atomic arrangement, and observed mutual reversible phase transition under As _4 flux.(3)We have investigated initial growth process of MnAs on GaAs (001) c (4×4) a, and found that phase transition from c (4×4) α to c (4×4) β took place very early stage of MnAs growth, which lead to apparent anomalous surface coverage.(4)We have investigated ballistic electron motion in Fe-layers grown on GaAs (001) by using ballistic electron emission spectroscopy (BEES), and found that penetration depth of ballistic electrons having energy ranging from 1.1 to 1.6 eV is decreasing with their energy and to be 2.7-1.5 nm.(5) We have observed magnetization orie ntation reversal induced by current injection at lowest threshold current density as low as 3x10^4A/cm^2 in GaMnAs/GaAs/GaMnAs double barrier magnetic tunneling junctions, so far.