The Study Of Resistive Switching In Ferroelectric Semiconductor BaTi_1-xNb_xO₃and Ferromagnetic Semiconductors Properties Of FeSi_1-xGe_x

Overwhelming advances in modern information technology and electronic industry brings new challenges to semiconductors. The multifunctionalization of semiconductors is the central task in scientific world today. As a result, some novel controllable degrees of freedom have been introduced. First of all, traditional logic and memory devices have touched their bottlenecks after their rapid development in the past few decades. Thus high density, scalable, low cost devices based on semiconductors but with a brand new mechanism are desired. Secondly, if we introduce spin into semiconductors, we get magnetic semiconductors. Carriers and spin can be controlled spontaneously in such systems, resulting in the great application value of spin field effect transistor (SFET) in future. In order to understand deeply about multifunctional semiconductors and move toward to practical applications, the ferroelectric induced resistive switching in BaTi0.998Nb0.002O3system and magnetism as well as transport property of Ge-doped FeSi ferromagnetic semiconductors are investigated in this dissertation. The main results are as follows:1, Ferroelectric induced resistive switching in BaTi0.998Nb0.00203systemA novel ferroelectric manipulated resistive switching phenomenon was observed in semiconducting ferroeleetrics BaTi0.998Nb0.002O3(BTNO). A series of programming tests were carried out on BTNO and it shown lots of outstanding characters such as nonvolatility, high repeating programmable capacity and fast response speed. The space charge density at grain boundaries (GBs) inside BTNO plays a key role on the transport properties of the system. And the charge density can be modulated by the ferroelectric polarization state according to the model we present. This model was proved by our further investigation and a prototype of ferroelectric resistance random access memory (FRRAM) was put forward in our work. A FRRAM combines the advantages of both resistance random access memory (RRAM) and ferroelectric random access memory (FRAM). More importantly, it also solves some key issues which have disturbed them for a long time. As a result, we think FFRAM has great potential for application in next generation memories.2, Magnetic and transport properties of room temperature ferromagnetic semiconductor FeSi1-xGexThe magnetic and transport properties of FeSi1-xGex alloys were investigated. A weak magnetic to ferromagnetic transition occurs at x=0.25, and then the system experiences a semiconductor to metal transition at x=0.4. Between x=0.25and x=0.4, the system always reveals a ferromagnetic semiconductor nature and the ferromagnetism keeps up to the room temperature. The magnetism before the semiconductor-metal transition temperature T, is induced by the weak itinerant exchange interaction according to Walfarth’s model. However, when T exceeds T,, the energy gap begins to close and thus this interaction in semiconductiong region is destroyed. As the ferromagnetism in FeGe comes from the strong itinerant DM interaction, it’s reasonable to conclude that the magnetism after Tt gradually is dominated by the DM interaction when the gap totally closed.