Development of novel III-nitride-based dilute magnetic semiconductors for application in magnetic tunnel junctions.

摘要

The advances in the synthesis and characterization of novel dilute magnetic semiconductors (DMSs), AlxCr1-xN and GaxCr 1-xN, are described. This class of materials is essential for the advancement of semiconductor-based spintronics, an emerging area that combines the functionality of both the charge and the spin degree of freedom of an electron. If this can be realized, it could possibly lead to a new class of devices with enhanced capabilities.; AlxCr1-xN and GaxCr1-xN thin films were gown by reactive molecular beam epitaxy (MBE). A thermochemistry approach was used in guiding and developing the growth of these DMSs. While an important goal was to achieve above room-temperature ferromagnetism, obtaining high crystal quality as well as maintaining its semiconducting properties is crucial for the integration of these films into devices.; Under optimized conditions, the experimental data indicated that Al xCr1-xN and GaxCr1-xN exhibit ferromagnetism with Curie temperatures above 900 K, the highest Curie temperature reported to date. Although prior literature has suggested that ferromagnetism in these materials are partly due to ferromagnetic secondary phases, extensive structural characterization using x-ray diffraction and transmission electron microscopy indicate homogeneous single-phase epitaxial films. Angular-dependent channeling Rutherford backscattering spectroscopy was used to quantify the fraction of Cr atoms on substitutional, interstitial, and random lattice sites. Films grown at 775°C indicate that 90% of the Cr atoms are sitting on substitutional sites., whereas films grown at 825°C only had 17%. The effect of the Cr position in the III-N lattice was found to have a profound effect on the magnetic and electrical transport properties.; The fabrication of magnetic tunnel junctions (MTJs) which utilize these DMSs were also investigated. Studies determining the feasibility of Ga xCr1-xN as a ferromagnetic electrode and AIN as a barrier material were carried out in planar MTJs processed by reactive ion etching.; In summary, this study revealed new insights into the fundamental properties of these novel ferromagnetic semiconductors and to assess their potential in achieving spin-dependent transport in semiconductor-based heterostructures.