Abstract

In the preparation process of negative electron affinity GaAs photocathodes, the p-type doped property is beneficial to photoemission, and the doping element is usually Be or Zn. In fact, C-doped GaAs material has been widely used due to its high activation rate, extremely low diffusion coefficient, and good thermal stability, whereas the influence mechanism of the C dopant on the performance of the GaAs photocathode is still unclear. In order to investigate the substitutional effect on C-doped GaAs, electronic structures and optical properties along with angular distribution of emitted photoelectrons are obtained by utilizing first-principles calculation based on density functional theory. The results show that C-doped GaAs is more likely to form a p-type doped feature in which the C dopant forms new levels in the forbidden band and reduces the energy gap as well as increasing the absorption coefficient and decreasing the reflectivity in the visible light band. In addition, the electrons emitted from the Γ-valley for C-doped GaAs have better directivity than those for pure GaAs, which is mainly ascribed to the smaller effective electron mass in the Γ-valley.

Highlights

  • The influence of dopant elements on the optoelectronic properties of negative electron affinity (NEA) III-V semiconductor photocathodes deserves deep understanding due to the rapid application development in low-light radiation detection,1 ultraviolet missile warning systems,2,3 underwater photoelectric imaging systems,4,5 high-speed imaging devices,6,7 and other fields.8–10 Among them, the NEA GaAs photocathode is one of the most widely used photocathodes owing to its high quantum efficiency, fast response time, designable response spectral range, and concentrated angular distribution of emitted photoelectrons.11–13 As is well known, the NEA GaAs photocathode should belong to the p-type semiconductor

  • In order to avoid interaction of atoms in the z direction, a vacuum layer of 15 Å is built in the calculation of the surface model, and the exchange correlation function adopted the generalized gradient approximation (GGA) functional proposed by Perdew, Burke, and Ernzerhof (PBE)

  • Both the valence band maximum and the conduction band minimum of the pristine GaAs material are located at the G point in k-space, which means that pristine GaAs is a typical direct bandgap semiconductor and the transition of the valence band electrons to the conduction band does not require the participation of phonons

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Summary

Introduction

The influence of dopant elements on the optoelectronic properties of negative electron affinity (NEA) III-V semiconductor photocathodes deserves deep understanding due to the rapid application development in low-light radiation detection, ultraviolet missile warning systems, underwater photoelectric imaging systems, high-speed imaging devices, and other fields. Among them, the NEA GaAs photocathode is one of the most widely used photocathodes owing to its high quantum efficiency, fast response time, designable response spectral range, and concentrated angular distribution of emitted photoelectrons. As is well known, the NEA GaAs photocathode should belong to the p-type semiconductor. The influence of dopant elements on the optoelectronic properties of negative electron affinity (NEA) III-V semiconductor photocathodes deserves deep understanding due to the rapid application development in low-light radiation detection, ultraviolet missile warning systems, underwater photoelectric imaging systems, high-speed imaging devices, and other fields.. The NEA GaAs photocathode is one of the most widely used photocathodes owing to its high quantum efficiency, fast response time, designable response spectral range, and concentrated angular distribution of emitted photoelectrons.. The NEA GaAs photocathode should belong to the p-type semiconductor. P-type doping can form a surface band bending region that is beneficial to the photoelectron emission. P-type doping can make the Fermi level be close to the top of the valence band, which is helpful for reducing the dark current caused by thermal emission.

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