First-principles Study On The Electronic Structures Of Low-dimensional Semiconductor Materials And Transport Characteristics Of Their Devices

Low-dimensional semiconductor materials are widely used in photodetectors,laser diodes,gas sensing,field-effect transistors?FET?,solar cells,and other fields due to their unique structures and physical properties.In this paper,based on first-principles calculations based on density functional theory?DFT?,the electrical and optical characteristics of phosphorus and phosphide?blue phosphorus,P₂C₂?and selenide?Sn Se,Ga₂Se Te?low-dimensional semiconductor materials were studied,and their potential device applications and device transport characteristics were explored based on their advantages.In addition,the electrical properties of the dislocations of the thin film were studied theoretically and experimentally,and the experimental results were consistent with the theoretical calculation results.The main research contents and conclusions are listed as follows:1.The electronic structures of P₂C₂ and Sn Se were studied by using first-principles,and it was found that they may have good chemical or physical adsorption characteristics for NO₂ gas molecules.By calculating parameters such as adsorption energy,equilibrium distance,and Mulliken charge transfer,as well as electronic local functions.It was found that there are a strong orbital hybrid,strong adsorption energy and superior charge transfer between the P₂C₂ monolayer and NO₂ gas molecules,indicating that the P₂C₂ monolayer is highly sensitive and selective to NO₂ gas molecules.Based on this,the characteristics of gas sensors based on P₂C₂ monolayer devices are further explored.The current-voltage?I–V?curves reveal that the adsorption of NO₂ can largely modify the resistance of P₂C₂ monolayer.In addition,the recovery time of the P₂C₂ sensor at T=300 K is estimated to be short?even shorter for higher temperature?for NO₂,which satisfies the demand for sustainable use.As for Sn Se monolayer,All the calculated molecules show physisorption nature on the Sn Se monolayer.The results demonstrate that Sn Se is sensitive to NO₂ gas molecules with moderate adsorption energy and superior charge transfer.Furthermore,only the adsorption of NO₂ can modify the densities of states of Sn Se near the Fermi level.The I–V curves reveal that the conductivity of the Sn Se monolayer is distinctly increased after NO₂ adsorption.The recovery time of the Sn Se sensor at T=300 K was estimated to be quite short for NO₂,which satisfies the demand for sustainable use.2.First-principles and nonequilibrium Green's function?NEGF?methods were used to study the electronic structure of blue phosphorene and its transport characteristics of FET devices.The calculated results indicate that ML blue phosphorene MOSFETs show excellent performances with ultrashort-channel length,which can meet the high-performance?HP?and low-power?LP?requirements of the International Technology Roadmap for Semiconductors?ITRS?in the next decade in the aspects of the on-state current,delay time,and power dissipation with proper doping concentration and introduction of the underlap?UL?structures.The performances of the ML blue phosphorene MOSFETs are superior to that of the MOSFETs based on arsenene,antimonene,In Se etc.,in terms of the on-state current at similar device size.At the same time,the effect of electron-phonon scattering on 10.2 nm-gate lengths ML blue phosphorene MOSFETs was studied.It was found that the on-state current with the scattering of the blue phosphorene device is degraded by 25.4%and 23.6%for HP and LP applications,which can also fulfill the HP and LP application target.The results show that ML blue phosphorene has the potential to instead of silicon as the channel material for ultrascaled FETs.3.The electronic and optical properties of Janus Ga₂Se Te monolayer were calculatedby the first-principles and find that it had the potential for solar cells.A graphene-Ga₂Se Te-graphene solar cell device structure was designed,in which the active region adopted stacked Ga₂Se Te ultra-thin cross-plane pn-junctions.It was found that the multilayer Ga₂Se Te solar cells give rise to a photocurrent exceeding that of 20 nm thick silicon film cell devices,and the maximum power conversion efficiency?PCE?of the double-layer Ga₂Se Te solar cell can reach 15.8%.The calculation results show that Ga₂Se Te is a potential material for preparing flexible photovoltaic devices.4.We used isotropic linear elasticity theory and DFT calculations to model the coreatomic structures of screw dislocations?TDs?of Ga N thin film and calculated corresponding electronic structures.The results show that screw dislocations with full-core structures are found to introduce both deep and shallow energy states within the energy gap dispersedly,while the open-core screw dislocations and the most edge dislocations introduce only shallow energy states.It was verified experimentally.The electrical properties of TDs in the Ga N layer were characterized using a conductive atomic force microscope?C-AFM?.It was found that full-core screw dislocations and mixed dislocations provided conductive paths for device leakage.The effects of edge dislocations and open core screw dislocations on the leakage current of the device are smaller than full core screw dislocations and mixed dislocations,which is basically consistent with theoretical calculations.