Interfacial Engineering Of Several Polar Semiconductors To Achieve Promoted Photoelectronic Properties

Compared with other semiconductor materials,polar semiconductors often have unique properties due to their spontaneous polarization characteristics,such as pyroelectric,piezoelectric and other important physical effects.Therefore,it has very important applications in solid-state devices such as photodetection,high-power lasers and other optoelectronic devices.The study of the properties of polar semiconductor materials plays an important role in improving the performance of their optoelectronic devices.The methods for performance regulation of semiconductor optoelectronic devices mainly include defect engineering,cavity engineering,and strain engineering.In this paper,several representative polar semiconductor materials(ZnO,GaN,InSe)are selected as the research objects,combined with cutting-edge testing technology,finite element simulation,first-principles calculation,etc.,to explore different control methods to achieve the regulation of optoelectronic properties.Based on Frank-Condon and Huang-Rhys models,we first proposed and proved that the relaxation rate of ZnO metastable center can be accelerated by increasing the phonon energy(excitation of LO phonons)and the phonon population(coherent control of phonons).Fabry-Perot cavity(FPC)structure was constructed to realize infrared detection of GaN under ultraviolet(UV)atmosphere for the first time.The structure of Au array was optimized by finite element simulation to further enhance the infrared detection performance of GaN.The phase transition from β-InSe to MC-InSe was first realized induced by indentation based on strain engineering,and the band structure of two-dimensional(2D)layered β-InSe was regulated.The main research contents of this paper were as follows:In chapter 1,we introduced the research background and significance of the subject.We briefly summarized the properties and application fields of polar semiconductor materials and introduced the properties and development direction of ZnO,GaN and InSe in polar semiconductor materials.Then the working principle,parameters and influencing factors of the semiconductor photodetector were introduced.The methods of controlling optoelectronic properties of semiconductor materials were reviewed in detail.Finally,the research purpose and the problems to be solved are proposed.In chapter 2,the relaxation process of metastable center in semiconductor materials was investigated.We selected ZnO as the research object,and analyzed the reasons of persistent photocurrent(PPC)generation and the relaxation kinetics of carriers in ZnO.Based on FrankCondon and Huang-Rhys models,we proposed to accelerate the relaxation of metastable center in ZnO by increasing phonon energy and phonon population.The relaxation time of metastable center was reduced from～1.48 h(5313 s)to～0.34 h(1223 s)for electron-LO phonon coupling by using infrared excitation.The importance of free electron concentration was demonstrated through energy band engineering at the Au/ZnO heterogeneous interface.Au NPs further accelerated the relaxation process of metastable center.The relaxation time can be reduced by～52 times from～1.99 h(7168 s)to～0.04 h(138 s).This provides an effective method to control the metastable center.In Chapter 3,the effect of ultrafast laser for the relaxation process of metastable center in ZnO was studied using ultrafast spectroscopy and theoretical analysis.It was proposed that the metastable center relaxation process was promoted by the coherent control of phonons.It was proved that the relaxation of metastable center can be accelerated by excitation of coherent acoustic phonons with 1064 nm picosecond laser,and the relaxation time was shortened by～1181 times to 4.5 s.The mechanism of coherent acoustic phonons was analyzed,and the photoinduced stress under different mechanisms was calculated.The main mechanism of stress induced by 1064 nm picosecond laser through multi-photon absorption and free electron absorption was the inverse piezoelectric effect,which lead to the generation of coherent acoustic phonons and increased the acoustic phonon population,thus accelerating the relaxation process of metastable center of ZnO.This provides valuable guidance for the development of novel quantum and optoelectronic devices based on optically manipulated metastable centers.In Chapter 4,the infrared absorption of GaN was enhanced by constructing FPC structure,so that the switching ratio of the current was increased to～43 times and the Schottky barrier height was increased from～0.54 eV to～0.65 eV by irradiating eGaN with 1064 nm laser.The modulation of the defect-assisted electron tunneling mechanism by pyroelectric field was proposed to realize current regulation process of GaN.The Au metasurface microarray structure constructed on GaN film with FPC can enhance the 1064 nm infrared intensity at the Au/GaN interface by Comsol Multiphysics simulation.The Au array was constructed by the direct laser writing on GaN surface,and the Au array can increase the optical absorption of 1064 nm near～50 times by the Comsol simulation.The current switching ratio of eAu-GaN under 1064 nm illumination increased to～1000,and the Schottky barrier height increased from～0.69 eV to～0.86 eV.In Chapter 5,indentation can induce the phase transition from hexagonal β-InSe to monoclinic MC-InSe.The critical pressure required for this transition was determined to be～4.03±0.16 GPa using a nanoindentation technique.Using confocal Raman spectroscopy,we verified that a new Raman mode at～144 cm-1 can be attributed to MC-InSe.The MC-InSe was in the form of nanocrystals of diameter ranging from 25 to 35 nm embedded in an amorphous InSe matrix at ambient conditions,which was unambiguously confirmed via high-resolution transmission electron microscopy.The indentation induced phase transition can make the bandgap of InSe blue shift from 1.26 eV to 1.88 eV and realize the regulation of the photoelectronic properties of InSe.The obtained results were discussed based on density function theory calculations.It has great potential for the realization of novel electronic devices in single-material systems by mechanically induced phase transitions.In chapter 6,we systematically summarized the subject and innovation of the whole paper,and makes a prospect for further research.The innovation of this paper lies in:(1)Based on the Frank-Condon and Huang-Rhys models,it is first proposed to accelerate the relaxation of the metastable center in ZnO by increasing the phonon energy(excition of LO phonons)and the phonon population(coherent control of phonons).The ZnO metastable center relaxation is experimentally accelerated by～4.3 times through 1064 nm infrared irradiation.What’s more,the relaxation of the metastable center in ZnO is further accelerated by～52 times through Au NPs by the Frohlich interaction.(2)The phonon population can increase by ultrafast laser excitation of coherent acoustic phonons,which improved the relaxation process of the ZnO metastable center by～1181 times.This not only provides an efficient method for manipulating metastable centers to improve the performance of semiconductor optoelectronic devices,but also broadens the application prospects of coherent state control of phonons.(3)We enhanced the infrared light absorption of GaN by constructing the FPC structure.By optically modulation of the Schottky barrier height,infrared photodetection of GaN under UV atmosphere is realized,and the current on/off ratio reaches-43.The modulation of the Frenkel-Poole emission tunneling mechanism by pyroelectric field was proposed to realize current regulation process of GaN.The Au array structure is optimized by finite element simulation,which further enhances the infrared detection performance of GaN under UV atmosphere.The current switching ratio has reached more than 1000,and the response time has reached 60 ms.This provides a new idea for the improvement of semiconductor infrared detection performance.(4)The phase transition from β-InSe to MC-InSe is realized by indentation induction,and the band structure of 2D layered β-InSe is controlled for the first time based on the strain engineering.This holds great potential for realizing novel electronic devices in a single material system through mechanically induced phase transitions.