MBE growth and spin injection measurements of ferromagnetic alloy nickel-manganese-indium on III-V semiconductors.

摘要

In this thesis, ferromagnetic metal/III-V semiconductor heterostructures were investigated for the development of spintronic devices. Particularly, three major research projects were carried out. First, spin injection from Fe into GaAs was studied. Second, the InAs-based resonant tunnel diode (RTD) was developed for spin detection. Third, epitaxial growth of single-crystal ferromagnetic Ni2MnIn thin films as a potential spin contact on InAs was demonstrated by molecular beam epitaxy (MBE).; Spin injection from Fe into GaAs was studied by using the Fe/(Al,Ga)As Schottky contact as the spin injector and the GaAs/(Al,Ga)As quantum well as the spin detector. Our results show that high delta-layer doping levels are detrimental to the electroluminescence polarization (ELP) signals while a uniformly doped n+-layer can improve the spin injection efficiency. An ELP signal as high as 20% was obtained for a spin light emitting diode sample with a uniformly doped n+-layer with a doping level of 5 x 1018/cm3.; The InAs/AlSb/GaSb/AlSb/GaSb/InAs RTD structure was developed as a potential spin detector. MBE growth procedures for InAs and AlxGa1-x Sb were established. InAs/AlSb/GaSb/AlSb/InAs RTD structures were grown and fabricated. The I-V characteristics of the devices show a peak-to-valley ratio of 3 and 10 at room temperature and 14 K, respectively.; As a promising spin contact on InAs, the growth of ferromagnetic Ni 2MnIn thin films on InAs (001) was demonstrated by MBE. At a growth temperature of 120°C, a transmission electron microscopy study confirms the epitaxial growth of Ni2MnIn films in the B2 structure on InAs (001). The epitaxial relationship was determined to be Ni2MnIn(001)100> || InAs(001)100>. The lower Curie temperature of the films (∼170 K), compared to that of bulk Ni2MnIn, is believed to result from the growth of Ni2MnIn in the B2 structure rather than the L21 structure. Curie temperatures of the Ni2MnIn thin films can be increased through annealing. For a sample grown at 120°C and annealed at 200°C, a Curie temperature as high as 330 K was obtained. The high Curie temperature is correlated to the Ni2MnIn in the partially L21-ordered structure.