Magnetoresistance Properties And Applications Of Semiconductor Silicon And Germanium

Magnetoresistance effect(MR)refers to the changing of material resistance under applied magnetic fields.The devices based on the MR effect has been widely used in many fields,such as computer,electric vehicles,magnetic storage,aerospace and magnetic detection.In this thesis,we mainly studied the electro-and magneto-transport properties of the two semiconductor materials—silicon and germanium.Hopefully we can apply them in the field of magnetic sensing in the future.Firstly,we made a two-terminal silicon-based device(Al/Ti/n+-Si/n-Si),and found that the I-V curve showed the behavior of current jump at a critical voltage,which made the device changing from a high resistance state(HRS)to a low resistance state(LRS).The critical voltage would increase under applied magnetic fields,so large positive MR(2450% at 0.07 T and 2520% at 0.1 T)would be observed in the transition region of resistance.Besides,the MR showed no signs of saturation even under 7 T(MR=7400%at 7 T).This huge MR effect is related to current filament induced by S-shaped negative differential conductance(SNDC).In addition,the MR would be enhanced by appropriately increasing the electrode spacing and width,or lowering the temperature.For example,when the temperature was decreased to 100 K,the MR at 7.65 V and 0.05 T could reach 2010%.Secondly,We studied the magnetoelectric transport properties of In/Ge/In device.With applied voltage increased,the electro-transport mechanism of the device transited from ohmic conduction to space charge conduction and finally to local impact ionization process.When the magnetic field was applied parallel to the sample plane and perpendicular to the current,tha carrier would recombine at different surfaces according to the polarity of the magnetic field,leading to an asymmetric MR effect.Through the structure parameter optimization,the device showed excellent MR performance both in low(80% at 0.1 T and 40% at 0.05 T)and high magnetic field(6300% at 7 T).Especially,a linear relationship between MR and the magnetic field(B)was presented at B<4 T,and the linearity could be maintained to 50 mT.Thirdly,based on the large and asymmetric MR effect of germanium,we designed a programmable logic devices controlled by voltage and magnetic field.It realized the COPY,NOT,AND,OR,NAND and NOR logic operations at room temperature.The germanium-base logic device provides a paradigm shift from transistor-based logic tothe magnetic-field-based logic,and has the advantage of simple structure,high logic output signal and ultra-low-threshold field.Fourthly,the MR of germanium was greatly enhanced with the aid of diode.It was observed that,increasing the width/length(W/L)ratio or choosing the diode with good rectification characteristic would make the MR further increased.The room-temperature MR value could reach 3×104% at 1.2 T and 200% at 0.02 T,respectively.This study may pave a way for the practical application of semiconductor material in the low-field magnetic sensing.