Spin-dependent transport characteristics across magnetic nanoscale junctions through doped IV and III/V semiconductors

We have studied spin-dependent transport across magnetic metallic strips deposited on doped Si and GaAs in a wide range of temperatures up to the ambient temperature, and found strong evidence of coherent spin transport through the magnetic metal into the semiconductors at the elevated temperatures. First, spin transport through Si doped GaAs was studied between two cobalt strips separated by a 100 mum. It was found that there was well-defined field modulated resistance variation in low magnetic field range (<100 Oersted) at T= 300 K. A moderate variation of 3% was observed in samples with light doping (~1014/cm³), which exhibited non-ohmic contact behavior demonstrating two oppositely polarized Schottky barriers for the two Co strips. The field modulation was found to be dependent on the current, and the temperature dependence of resistance with excitation energy was close to that of the Si dopant. Further, tunneling characteristics were measured on e-beam lithographically patterned spin-dependent tunneling (SDT) lines on n-doped Si, to study ballistic transport from ferromagnetic nano-lines via AlOx barrier into group IV semiconductor. The measurement was done using dual lock-in amplifiers, multi-channel voltmeter, in adder circuit with low noise operational amplifiers. Nano-scaled 100 nm STD junction lines closely spaced (100 nm) were fabricated on P doped Si as injection contacts. The measured I-V characteristics and the differential conductance (dI/dV) versus the bias voltage (V) versus temperature, from 84 to 300 K, through a STD junction showed weak temperature dependences. For example, from 84 to 250 K in the measured dI/dV at low bias range was found to be independent of T, which demonstrated clearly ballistic transport from ferromagnetic nano-contacts into the semiconductor.