We have succeeded in observing the magnetoresistance effect (MR) of spin valve device using semiconductor single walled carbon nanotube (s-SWNT) quantum effect device.
The s-SWNT quantum effect device was fabricated as below. The s-SWNT was grown by chemical vapor deposition on a p-type silicon wafer with a thermally grown oxide. Ferromagnetic metal of Co was deposited on the both side of the s-SWNT for source and drain electrode, and the back side of Si substrate were coated with Ag paste for back gate electrode. The channel length was 73 nm. Finally, SiO2 was deposited on the surface of the device as passivation film. Thus, very short channel back gate type s-SWNT quantum effect device was fabricated.
The s-SWNT quantum effect shows quantum interference characteristic at range of gate voltage VG from -18 V to -30 V. Conductance peaks are attributed to the quantum interference of hole in s-SWNT. We estimated the quantum interference length of hole from period of the conductance peaks, which was 55 nm. Because of compatibility of designed channel length and estimated quantum interference length, we believe the quantum interference of hole arose in the whole length of s-SWNT channel.
We observed magnetic field dependence of resistance characteristic. Magnetic field was applied to parallel direction of s-SWNT axis. Magnetic field was applied from 1000 G to -1000 G (forward) after that from -1000 G to 1000 G (backward). In the forward sweep of the magnetic field, the resistance became large at the range from 200 G to-400 G. This increase of resistance might be corresponding to the spin flip of one of the ferromagnetic electrode. At smaller magnetic field than -500 G in the forward sweep, the resistance became small again. This decrease of resistance might be corresponding to the spin flip of another ferromagnetic electrode. In the backward sweep of the magnetic field, the increase and decrease of the resistance was not observed. The reason might be spin flip of transporting hole by trapped charge in trap site of SiO2 around the s-SWNT.
Thus, we succeeded in observing the MR in the quantum interference regime of single walled carbon nanotube. |