Molecular Beam Epitaxy and Scanning Probe Microscopy of manganese arsenic based heterostructures for spintronics
Hegde, Shridhar N.
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Research in the field of semiconductor spintronics aims to exploit the electron spin degree of freedom, in addition to its charge, for logic device applications. Progress in semiconductor spintronics has been impeded by the lack of an efficient spin polarizer to polarize spins for injection into semiconductors. The room temperature ferromagnet MnAs, has emerged as an important candidate in this regard. The growth of this interesting material using Molecular Beam Epitaxy (MBE) on two technologically relevant materials - GaAs and Si, is discussed in the first part of this dissertation. The self-assembly of MnAs on Highly Oriented Pyrolytic Graphite (HOPG) as a means to study this material separated from substrate effects is also explored. The MnAs film properties are characterized using Vibrating Sample Magnetometer (VSM) and Scanning Probe Microscopy (SPM). Diffusion of Mn atoms into the GaAs substrate at the MnAs/GaAs interface is studied at atomic resolution using the cross sectional Scanning Tunneling Microscope (XSTM) technique. The final part of this dissertation deals with the use of MnAs as a spin polarizing contact to electrically inject spins into GaAs quantum wells. This is accomplished by integrating MnAs with a conventional n-i-p GaAs quantum well LED structure, to form a spin LED. The electroluminescence (EL) of such spin LEDs is circularly polarized. An analysis of the EL shows that the polarization of electron spins injected into the GaAs QW region is 56% at 7K, which is much higher than any previously published result. The spin injection persists even at room temperature with an EL circular polarization of ~6% at 300K. This work demonstrates that MnAs may be the ideal material for use as a high efficiency spin injector in semiconductor spintronics.