Study On Theories And Devices Of Hot-Electron And Hot-Hole Photodetection

As a new type of photodetection scheme,the hot-carrier(including hot-electron and hot-hole)photodetector based on the principle of internal photoemission has the benefits of breaking the semiconductor bandgap limitation,room-temperature&zero-bias operating,and high tunability in terms of the operating wavelength/detection bandwidth/polarization,and thus has attracted very extensive attention.However,factors including the thermalization loss caused by scattering activities,the blocking of the Schottky barrier,the momentum mismatch,etc.,lead to the generally low optoelectronic performance.This thesis starts with the internal physical process of the hot-carrier devices and conducts a comparable study on hot-electron and hot-hole devices.The Monte Carlo calculation model is used to analyze the influence of different geometric structures and sizes on the efficiency of hot carrier injection.The main research contents of this paper are summarized as follows:Firstly,the metal/semiconductor contact and internal photoemission theory involved in hot-carrier devices were introduced.Employing the first-principles,the hot-carrier energy distribution,relaxation time(lifetime),and mean free path were systematically explored,and the intrinsic mechanisms of hot-carrier collection were analyzed.Besides,the microscopic hot-carrier theoretical models including electromagnetic and hot-carrier transport(traditional three-step theoretical model and Monte Carlo simulation method)analysis were introduced in detail.Secondly,taking a typical Au/Si Schottky contact as an example,a comparable study on the hot-electron and hot-hole photodetection was performed.It was found that there are obvious differences in the band bending of Schottky junction,energy distribution,mean free path,and injection efficiency.Compared with hot electrons,the proportion of high-energy hot holes is higher,the transport and the injection efficiency are larger,resulting in higher quantum efficiency and photoresponsivity.However,lower Schottky barrier of hot-hole device causes higher dark current and lower detectivity.In addition,the effects of changing barriers and resonance wavelengths on the photoelectric performance of hot-electron and hot-hole devices were analyzed.Thirdly,considering the hot-electron emission in gold-titanium dioxide system,the Monte Carlo method is used to study and analyze the injection efficiency of single-and double-junction planar structures,cylindrical structures,and single-and double-junction core-shell structures.At the incident photon energy of 3eV,the single-junction planar structure with a 5 nm-thickness of Au has an injection efficiency of 5%,exceeding the Fowler efficiency.Compared with the single-junction structure,the double-junction planar structure of the same size has an increased injection efficiency.For the double-junction core-shell structure based on TiO2-nanowire/Au/TiO2,when the Au thickness of 5 nm,nanowire radius of 50 um and the incident photon energy of 3 eV,the injection efficiency is about 1.5 times of the Fowler efficiency.However,when the Au size is increased to 50 nm,the injection efficiency of the double-junction core-shell structure is reduced to 2.14%.Since the injection efficiency increases with decreasing TiO2 radius,when the radius is 5 nm,the injection efficiency is about 2.18%higher than that of the cylindrical structure(2.17%).The results show that the geometry and size of the structure will affect the injection efficiency of hot electrons.Especially for small-size structures,the injection efficiency is significantly improved to exceed the Fowler efficiency.The comparable study on hot-electron and hot-hole photodetection clarifies the intrinsic physical differences between hot-electron and hot-hole devices,and compares the corresponding key performance parameters of photodetectors.In addition,compared with the traditional three-step model,the Monte Carlo simulation method is more rigorous in addressing the basic physical processes of hot carriers.This study is useful for a better understanding the nature of hot-carrier photodetection as well as promoting the optimization design for the hot-carrier devices.