First Principle Study On Electronic Structure And Properties Of Low Dimensional CdSe And ReS₂ Materies

With the rapid development of electronic industry,the characteristic length of silicon based electronic components has reached the physical limit.In order to further extend the Moore’s law,characteristic size of devices has reduced into the nanometer level,which forces people to look for new semiconductor materials with lower dimensions.Low-dimensional semiconductor nanomaterials have unique properties in electronics,optics,mechanics,chemistry and so on.They are exhibiting different physical and chemical properties which has not found in bulk materials.Therefore,the analysis and regulation of the performances in low-dimensional semiconductor materials can promote the designment and preparation of novel high-performance semiconductor devices.Based on first-principle calculation,the influences of strain on the carrier mobility of one-dimensional CdSe nanowires and two-dimensional single-layer ReS₂ are analyzed.For one-dimensional CdSe nanowires,the influences of stress magnitude and nanowire size on carrier transport properties are mainly discussed.And for two-dimensional single-layer ReS₂,the influences of direction and size of strain on carrier transport properties are considered.In addition,the geometry,binding energy,electronic structure and bonding mode of CdSe-metal contact are analyzed.The main contents of this thesis are as follows:（1）The energy band structure,elastic modulus,deformation potential,carriers effective mass and mobility of CdSe nanowires with three different lateral dimensions（1.2 nm,1.6 nm,and 2.4 nm）are systematically investigated under different stress conditions（-10%-10%）.The results show that CdSe nanowire is always a direct band gap material,and its band gap decreases as the applied stress increases,no matter how much stress is applied.By comparing different sizes of CdSe nanowires,it can be found that nanowires with smaller lateral dimensions have higher carrier mobility.When a-10%stress is applied to the CdSe nanowire with a lateral dimension of 1.2nm,the maximum electron mobility and hole mobility are 2890 cm²·V^-1·s^-1 and 2273cm²·V^-1·s^-1 respectively.（2）The changes in band structure,elastic modulus,deformation potential,carrier effective mass and mobility for two-dimensional single-layer ReS₂ are computed under the application of-5%-5%stress.At this time,the uniaxial stress on b or c direction,and biaxial stress on b and c direction were discussed.The results show that the two-dimensional single-layer ReS₂ has strong anisotropy,and the stress applied in different directions has a great change to the two-dimensional single-layer ReS₂.When stress is applied in the c direction,the electron mobility reaches a maximum value of 6393 cm²·V^-1·s^-1,and when the maximum value is adapted,the transport direction is along the c direction,and the applied stress is 5%.In the case of biaxial stress,the transport direction is in the b direction,and the hole mobility reaches a maximum value of 3208 cm2·V^-1·s^-1 at the-5%stress.Therefore,the single-layer ReS₂ with appropriate stress will have higher carrier mobility,electron mobility can be increased up to about 5 times,while hole mobility can be increased up to about25%.（3）The properties of nano-CdSe in contact with Cu,Ag and Au are analyzed.Through the analysis about the geometric structure,binding energy,electronic structure and bonding mode,it is found that the system formed by the contact of nano-CdSe with metal still exhibits good metallicity,and the energy band structures of these systems are mainly dominated by metals.The mismatches between nano-CdSe and Cu,Ag and Au are not high.Among which the mismatch with Au is the lowest,is only about 2.5%,which indicates that nano CdSe can form better contact with Au.In addition,the calculation results of the binding energy are all positive values,indicating that the system will release heat during the bonding process.This means that the metal-semiconductor contacts all have good stability.