Electro-and Magneto-transport Properties Of Amorphous Carbon, Gallium Arsenide And Silicon

Amorphous carbon and semiconductor materials have special properties. Theirresistance states can be controlled by multi-fields, such as electrical and/or magneticfield. Amorphous carbon has attracted lots of attentions due to their various electro-andmagneto-transport phenomena and broad applications. The commonly usedsemiconductors, such as silicon (Si) and gallium arsenide (GaAs), are also widely usedin industry. In this dissertation, we focused on the electro-and magneto-transportproperties of amorphous carbon, gallium arsenide and silicon.Firstly, a series of pure amorphous carbon films were grown on glass substrate atdifferent temperatures by pulsed laser deposition (PLD) method. It was found theconduction mechanisms of these films were mainly hopping. As the depositiontemperature increased from300to600°C, hopping mechanism changed fromEfros–Shklovskii variable range hopping (ES–VRH) to the combination of ES–VRHand phonon assisted hopping. Magnetoresistance (MR) at different measurementtemperature and magnetic field were found all positive. MR showed no tendence ofsaturation as magnetic field increased. Moreover, the MR values decreased rapidly asthe measuring temperature increased. We ascribe the MR mechanism to wave-functionshrinkage effect by quantitatively analysis.Secondly, based the results of pure amorphous carbon films, iron was intentionallydoped into the amorphous carbon matrix at500°C by PLD. It was also found that, theconduction mechanism at low temperature evolved from the combination of ES–VRHand phonon assisted hopping to simple phonon assisted hopping as the iron contentincreased. Intesestingly, MR sign change was observed in these iron doped amorphouscarbon films. We propose the competition of wave function shrinkage effect, whichcauses positive MR, and spin related scattering effect (including the low field saturatinggiant MR effect and the high field saturating Brillioun-type giant MR effect), whichresults in negative MR, is responsible to MR phenomena.Thirdly, the room temperature appearance MR of GaAs was greatly enhanced bythe introduction of diode. It was observed that, the introduction of diode will effectivelyimprove value of appearance MR and lower power assumption. The appearance MRvalue could reach2,600%at1.2T at room temperature. The corresponding low field MR sense ability could reach44%at0.06T, and the power assumption is in the order ofsub Watt. It may help the practical application of GaAs in magnetic sensing.Fourthly, we developed a Si–SiO2–MgO nonvolatile resistive switching devicebased on Si. The device would change its resistance states at certain voltage (Vt). It wasshown that Vtcould shift reproductively under positive and negative larger currentpulses. When reading voltage was chosen in the shifting range of Vt, nonvolatileresistive switching effect with on/off ratio of10, endurance of more than200, andretention of more than104s was obtained. In addition, the external magnetic field couldreversibly suppress the resistive switching effect and yield a MR on the order of103%at1T. We propose that resistive switching and magnetic response comes from silicon, andthe nonvolatile behavior is realized by MgO layer.