Study On The Piezotronic Effect In Nitride Micro/nanowires

Group Ⅲ-nitrides have been widely used in various electronic and optoelectronic devices due to many advantages including adjustable,direct band gap,high thermal conductivity,high breakdown electric field,high radiation resistance and stable physical and chemical properties.The coupling of the piezoelectric effect and semiconductor effect of group Ⅲ-nitrides brings unique physical properties,which in turn opens up a unique research field-piezotronic effect.The piezotronic effect is to control the distribution and transmission of carriers in a semiconductor through the polarization charge(piezoelectric potential)induced by strain.On the other hand,for microscale and nanoscale group Ⅲ-nitride materials,some novel phenomena will appear due to the reduction in size and changes in the physical and chemical properties of the material,showing optical,electrical,and mechanical properties on a macroscopic scale.Moreover,compared with bulk materials,strong piezoelectric polarization can be generated inside the materials under very small mechanical excitation conditions,thus it is easier to achieve ultra-high sensitivity and gain for piezoelectric semiconductor devices using these materials.Therefore,it is very important to study the piezotronic effect in the groupⅢ-nitride micro-nano structure.However,in recent years,the research and theories of piezotronic effect based on group Ⅲ-nitride micro/nanowires have not been in-depth,and further development and research are needed.This dissertation constructs different micro/nanowire structures(GaN,AlGaN/AlN/GaN,InGaN/GaN MQW)based on group Ⅲ-nitride materials,and explores the coupling effect between semiconductor effect and piezoelectric effect in group Ⅲ-nitride micro/nanowires.The main research content includes the following four aspects:1.Based on the PN heterojunction structure and Schottky junction structure,taking wurtziteGaN nanowires as an example,the theory of piezotronic effect was elaborated,including the theory of piezoelectric potential regulating energy band and current density equation.2.Three kinds of Ⅲ-nitride micro/nanowires(GaN microwires,InGaN/GaN quantum well heterojunction microwires and AlGaN/AlN/GaN heterojunction nanowires)were prepared using the top-down method.The high-quality epitaxy structure was grown by metal organic compound chemical vapor deposition.And then we used micro-nano processing technology(including ultraviolet lithography,inductively coupled plasma etching,electrochemical stripping,etc.)to obtain microscale and nanoscale structure nitride materials.X-ray diffraction,transmission electron microscopy and other material characterization methods have proved that the experimental had obtained high-quality nitride micro/nanowire.In addition,Raman spectroscopy and finite element simulation showed that the residual stress the stripped heterojunction nanowire was reduced,which had a good mitigation effect on the internal polarization of the heterojunction.3.Three strain sensor devices were constructed using the prepared micro/nanowires,and the mechanism and regulation of stress and electrical characteristics on the interface characteristics ofGaN/Ag Schottky junction,InGaN/GaN MQW heterojunction and AlGaN/AlN/GaN heterojunction were explored.Studies have shown that the direction of the piezoelectric polarization(piezoelectric potential)caused by compressive stress and tensile stress was opposite,which leads to opposite effects on the regulation of interface energy band and electrical transmission characteristics.In addition,due to the change of the polarization charge density at the interface,it will lead to changes in the concentration and distribution of carriers at the interface,which has an important impact on the electrical transmission characteristics.4.We used the semiconductor device simulation software(Atlas)to simulate the heterojunction device,and further analyze and verify the influence of strain on the heterojunction energy band,the distribution of piezoelectric potential and carriers.Through the above research,the research on piezotronic effect in nitride materials has been further enriched,and this also provides a theoretical basis for the design of new devices related to nitride micro/nano materials.