Ion implantation of gadolinium in compound semiconductor materials and potential spintronic device applications.

摘要

As device dimensions have continued to shrink, atomistic scale fluctuations in material properties are beginning to limit continued improvements in device performance. Various technologies are being pursued to overcome this problem. Spin transport electronics, or spintronics, has been proposed as an attractive approach. This technology utilizes the spin of the electron, in addition to the charge of the electron, to transmit information through a device. The most promising materials for spintronic device applications are dilute magnetic semiconductors, which are formed when dilute amounts of magnetic atoms are incorporated into semiconductor materials. Recently, ion implantation has been studied as the incorporation method of magnetic ions into a host semiconductor material system for potential spintronic applications. This method provides excellent control over the quantity of the implanted ion and the resultant magnetic properties of the implanted material.;For this study, the compound semiconductor materials GaN, ZnO, and GaAs are examined as target materials for Gd ion implantation. Before implantation, these materials exhibited ferromagnetic behavior without the known presence of magnetic impurities and with a dependence on the applied magnetic field/sample surface orientation. Measuring the magnetic properties of these materials with a perpendicular orientation between the applied field and the sample surface exhibited a larger magnetic signal than examining with a parallel orientation between the applied field and sample surface, described in this work as an anisotropic enhancement effect. Ferromagnetism was demonstrated in hysteresis loops visible at both low temperature (10 K) and room temperature. The ferromagnetic mechanism occurring in the non-implanted materials is speculated as being due to anion-related defects (vacancies and interstitials).;Ferromagnetism was also demonstrated in the implanted compound semiconductor materials. Implanting Gd ions into GaN has resulted in this material exhibiting ferromagnetic behavior before any thermal annealing treatment. Co-implanting Si ions with Gd ions in GaN also shows room temperature ferromagnetism and a larger magnetic moment than the same GaN only implanted with Gd. Additional studies into the effects of Gd ion implantation on the magnetic properties of another wurtzite crystal structure compound semiconductor material (ZnO) and a small band gap semiconductor material (GaAs) provide additional insight into the ferromagnetic mechanism present in these materials. The mechanism occurring in the implanted materials is speculated as being due to interactions between the native defects and defects introduced during implantation with the implanted Gd. This interaction may be caused by long-range spin polarization that is demonstrated by the large magnetic moments observed in this work. Anion-related defects (vacancies and interstitials) appear to be the most likely defects to exhibit a spin orbit coupling with the implanted Gd atoms based on studies of implanted p-GaN and n-GaN. The effects of thermal annealing on the magnetic properties of the implanted thin films have also been investigated in implanted GaN and demonstrated that annealing does reduce the ferromagnetic ordering due to the decreased defect density as a result of the repaired lattice damage.;Based on these results, ion implantation provides an exemplary method to control the amount of incorporated magnetic ions and results in desirable magnetic properties in the implanted materials for spintronic applications. The ferromagnetic mechanism occurring in the implanted materials appear to rely on the type and density of defects interacting with the magnetic impurity implanted into the compound semiconductor material. The next step would be to further develop a model predicting the ferromagnetic mechanism exhibited by the implanted materials and then leveraging that mechanism to select the optimal compound semiconductor material/implant species and dose combination to create a functional spintronic device.