Materials Processing for Ferromagnetic Wide Bandgap Nitride Heterostructures

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This project will investigate advanced materials processing methods that do not disrupt spin-injection and transport in order to polarize, inject, transport, control, store and detect spins in semiconductors. The discovery of ferromagnetism in (In, Mn)As and (Ga,Mn)As opens an opportunity to explore the combination of high purity heterostructures and ferromagnetism. However the low Curie temperature for these materials (35K and 110K, respectively), limits their practical impact; in sharp contrast, (Ga,Mn)N is predicted to have a TC ~400K. This project will address the following topics: (i) development of low resistance p-ohmic contacts with sharp metal/semiconductor interfaces to allow efficient injection of spin-polarized currents into various heterostructures, e.g., (Ga,Mn)N/GaN, (Ga,Mn)N/InGaN; (ii) the development of appropriate plasma chemistries for equi-rate and selective dry etching of (Ga,Mn)N and related materials. For etching Mn, high density F2-based plasma chemistries have been successful. The normal Cl2-based chemistries for GaN will need to be altered in order to obtain equi-rate removal of all three lattice constituents in the (Ga,Mn)N; (iii) implantation/isolation needed in selective area doping for contact formation and for intra-device electrical and optical isolation. It is expected to achieve efficient doping of (Ga,Mn)N using Si+ for n-type and Mg+/P+ for p-type doping. The thermal stability of the (Ga,Mn)N during annealing will also be explored, in order to study formation of other phases or precipitates; (iv) examine the interaction of H with Mn-if passivation occurs, this will lower TC. The thermal stability of the effect, the reactivation kinetics (both thermal and by minority-carrier injection) and the H diffusivity, will be investigated; (v) fabrication of various test structures to enable a measurement of the spin injection efficiency-these include a GaMnN/AlGaN/GaN light-emitting diode and a GaMnN spinfet. The significance of the research will be the development of an understanding of how to process (Ga,Mn)N to achieve efficient spin injection and transport, as the basis for novel device structures.%%%The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important aspects of electronic/photonic devices. The basic knowledge and understanding gained from the research is expected to contribute to improving the perform-ance and stability of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.***