We designed two transmission-mode GaAs/AIGaAs photocathodes with different AlxGa1-xAs layers, one has an AlxGal-xAs layer with the Al component ranging from 0.9 to 0, and the other has a fixed AI component 0.7. Using ...We designed two transmission-mode GaAs/AIGaAs photocathodes with different AlxGa1-xAs layers, one has an AlxGal-xAs layer with the Al component ranging from 0.9 to 0, and the other has a fixed AI component 0.7. Using the first-principle method, we calculated the electronic structure and absorption spectrum ofAlx Ga1-x As at x = 0, 0.25, 0.5, 0.75 and 1, calculation results suggest that with the increase of the A1 component, the band gap of AlxGa1-xAs increases. Then we activated the two samples, and obtained the spectral response curves and quantum efficiency curves; it is found that sample 1 has a better shortwave response and higher quantum efficiency at short wavelengths. Combined with the band structure diagram of the transmission-mode GaAs/AIGaAs photo- cathode and the fitted performance parameters, we analyze the phenomenon. It is found that the transmission-mode GaAs/AlGaAs photocathode with variable AI component and various doping structure can form a two-stage built-in electric field, which improves the probability of shortwave response photoelectrons escaping to the vacuum. In con- clusion, such a structure reduces the influence of back-interface recombination, improves the shortwave response of the transmission-mode photocathode.展开更多
To theoretically research the influence of a varied Al component on the active layer of AlGaN photocathodes,the first principle based on density functional theory is used to calculate the formation energy and band str...To theoretically research the influence of a varied Al component on the active layer of AlGaN photocathodes,the first principle based on density functional theory is used to calculate the formation energy and band structure of AlxGa（1-x）N with x at 0,0.125,0.25,0.325,and 0.5.The calculation results show that the formation energy declines along with the Al component rise,while the band gap is increasing with Al component increasing.AlxGa（1-x）N with x at 0,0.125,0.25,0.325,and 0.5 are direct band gap semiconductors,and their absorption coefficient curves have the same variation tendency.For further study,we designed two kinds of reflection-mode AlGaN photocathode samples.Sample 1 has an AlxGa（1-x）N active layer with varied Al component ranging from0.5 to 0 and decreasing from the bulk to the surface,while sample 2 has an AlxGa（1-x）N active layer with the fixed Al component of 0.25.Using the multi-information measurement system,we measured the spectral response of the activated samples at room temperature.Their photocathode parameters were obtained by fitting quantum efficiency curves.Results show that sample 1 has a better spectral response than sample 2 at the range of short-wavelength.This work provides a reference for the structure design of the AlGaN photocathode.展开更多
基金supported by the National Natural Science Foundation of China(Nos.91433108,61301023)
文摘We designed two transmission-mode GaAs/AIGaAs photocathodes with different AlxGa1-xAs layers, one has an AlxGal-xAs layer with the Al component ranging from 0.9 to 0, and the other has a fixed AI component 0.7. Using the first-principle method, we calculated the electronic structure and absorption spectrum ofAlx Ga1-x As at x = 0, 0.25, 0.5, 0.75 and 1, calculation results suggest that with the increase of the A1 component, the band gap of AlxGa1-xAs increases. Then we activated the two samples, and obtained the spectral response curves and quantum efficiency curves; it is found that sample 1 has a better shortwave response and higher quantum efficiency at short wavelengths. Combined with the band structure diagram of the transmission-mode GaAs/AIGaAs photo- cathode and the fitted performance parameters, we analyze the phenomenon. It is found that the transmission-mode GaAs/AlGaAs photocathode with variable AI component and various doping structure can form a two-stage built-in electric field, which improves the probability of shortwave response photoelectrons escaping to the vacuum. In con- clusion, such a structure reduces the influence of back-interface recombination, improves the shortwave response of the transmission-mode photocathode.
基金supported by the National Natural Science Foundation of China(Nos.61308089,6144005)the Public Technology Applied Research Project of Zhejiang Province(No.2013C31068)
文摘To theoretically research the influence of a varied Al component on the active layer of AlGaN photocathodes,the first principle based on density functional theory is used to calculate the formation energy and band structure of AlxGa（1-x）N with x at 0,0.125,0.25,0.325,and 0.5.The calculation results show that the formation energy declines along with the Al component rise,while the band gap is increasing with Al component increasing.AlxGa（1-x）N with x at 0,0.125,0.25,0.325,and 0.5 are direct band gap semiconductors,and their absorption coefficient curves have the same variation tendency.For further study,we designed two kinds of reflection-mode AlGaN photocathode samples.Sample 1 has an AlxGa（1-x）N active layer with varied Al component ranging from0.5 to 0 and decreasing from the bulk to the surface,while sample 2 has an AlxGa（1-x）N active layer with the fixed Al component of 0.25.Using the multi-information measurement system,we measured the spectral response of the activated samples at room temperature.Their photocathode parameters were obtained by fitting quantum efficiency curves.Results show that sample 1 has a better spectral response than sample 2 at the range of short-wavelength.This work provides a reference for the structure design of the AlGaN photocathode.
