Study on spin device characteristic having p-n-p structure using GeTe based ferromagnetic semiconductors

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We have studied on the growth of GeTe based ferromagnetic semiconductors by molecular-beam epitaxy (MBE) method and fabrication of ferromagnetic tunnel junction (MTJ), and obtained the following results.1. It was found that the crystallinity and magnetic properties of GeTe based ferromagnetic semiconductors strongly depended on Te/magnetic ion flux ratio. It was confirmed that crystallinity of the film on a SrF_2 substrate was better than that on a BaF_2 substrate. The obtained Curie temperatures were 200 K for Ge_<1-x>Mn_XTe with x=008 and 190 K for Ge_<1-x>Cr_XTe with x=0.07, respectively.2. MTJs having p-n-p structure using n-type semiconductor CdS barrier were grown by ICB method and the tunnel current was observed for MTJ with CdS barrier thickness of 3.4 nm. The estimated barrier height using Simmons equation was 0.28 eV which was quite small compared to the designed value (2.1 eV). However, tunnel magnetoresistance was not obtained. MTJs were also grown by MBE and successfully obtained GeTe/GeMnTe/CdS/GeMnTe epitaxial films.3. MTJs with barrier layer of p-type semiconductor ZnTe, ferromagnetic insulator EuS and SrF_2 were fabricated. Epitaxial growth on a BaF2 substrate by using MBE method was confirmed in both multilayers with ZnTe and EuS barrier layers. Magnetoresistance ratio of 4.2 % at 10 K was obtained in the GeTe/GeMnTe/EuS(2 nm)/GeTe structure. The estimated barrier thickness from I-V characteristics using Simmons equation agreed well with the designed value and the barrier heights were 0.88-1.07 eV.