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To improve the noise performance of low-ligh-level (LLL) image intensifiers, the evaluation of the noise characteristics of a typical generation III image intensifier has been made through the measurement of signal to noise ratio at the output end (SNR out ) of this image intensifier in different work conditions. One of the most meaningful work is to discuss the effect of the pro-proximity pulse voltage applied between photocathode and microchannel plate (MCP) on the SNR out of a sample of LLL image intensifier (2008III138). The experimental result shows that the optimal values of voltage across GaAs photocathode and that across MCP are −300 V and 800 V, respectively. More importantly, the optimal values of high level, low level, and duty circle of the pro-proximity pulse voltage are −300 V, 0.2 V, and 60%, respectively. This research will provide a theoretical guide and experimental support for developing low noise LLL image intensifiers.

In practice, for a higher signal to noise ratio of the solar-blind ultraviolet (UV) image intensifier, one of the most meaningful work is to effectively evaluate its noise characteristics and to obtain suitable work voltages. In this paper, we have proposed an evaluation method and then implemented an effective evaluation of the noise characteristics of a typical solar-blind Cs 2 Te UV image intensifier, through the measurement of signal to noise ratio at the output end (SNR out ) of this image intensifier in different work conditions. The evaluation results show that the SNR out of a Cs 2 Te UV image intensifier increases as the photocathode voltage and the voltage across MCP increase within an appropriate range. Additionally, the voltage across phosphor screen has almost no impact on the SNR out . More specifically, the suitable values of Cs 2 Te photocathode voltage, the voltage across MCP and the voltage across phosphor screen are −300 V, 800 V, and 4500 V, respectively.

To improve the resolution capabilities of MCP, numerical simulation of the MTF of MCP has been made. Solving the electron trajectory equation, we obtain the potential distribution of MCP, and then obtain the electron trajectory in MCP. On this basis, a group of MTF curves are plotted by varying the tilt angle, the channel diameter, and the output end spoiling depth, individually. The simulation results show that in a moderate range a larger the tilt angle, a smaller the channel diameter, and a deeper the output end spoiling depth can improve the resolution of MCP significantly, according to the state of the art. Research on the effect of the above parameters on the resolution properties of MCP will provide a theoretical support for developing MCP with high resolution and further improving the resolution of image intensifiers.

Using plane-wave ultrasoft pseudopotential method based on density functional theory (DFT), the influence of Zn atoms on Cs activation process of NEA GaAlAs photocathodes is researched. The Zn-induced E-Mulliken population and ionicity change are analyzed, the influence of Zn on average dipole moment and work function are researched and the density of state and band structure of Cs adsorbed Ga 0.5 Al 0.5 As (0 0 1)β 2 (2 × 4) reconstruction surface before and after Zn doping are compared. Results show that Zn doped Ga 0.5 Al 0.5 As (0 0 1)β 2 (2 × 4) reconstruction surface shows Negative Electron Affinity (NEA) state when Cs coverage is 0.75 mL.

In 0.53 Ga 0.47 As is an important material for the shortwave near-infrared negative electron affinity photocathodes. As we all known, doping is a necessary step for the formation of the negative electron affinity and zinc is a traditional substitutional element to generate the P-type semiconductor. The In 0.53 Ga 0.44 Zn 0.03 As and In 0.50 Ga 0.47 Zn 0.03 As were formed from In 0.53 Ga 0.47 As by a zinc atom substituting a gallium atom or an indium atom in the article. The atom structures, the band structures and the populations were studied by the first principle method for these two supercell models. Two problems, how the zinc-doping change the characters of intrinsic In 0.53 Ga 0.47 As and the differences between In 0.53 Ga 0.44 Zn 0.03 As and In 0.50 Ga 0.47 Zn 0.03 As, were solved by the research. Firstly, the atom structures were changed and the band gaps were narrowed after zinc doping. The ionicity was enhanced which is agreed with the character of P-type semiconductor. Secondly, there were small differences between the two supercells in electronic structures. Therefore, there is no need to consider which kind of atom to be substituted during the material growth for the near-infrared InGaAs photocathode.

In order to study the influence of interstitial point defects on the optical properties of Ga0.75Al0.25N, three Ga0.75Al0.25N bulk models with Ga, Al, and N interstitial defects were built. And the band structure, dielectric function, complex refractive index, absorption coefficient, reflectivity, and loss function of pure Ga0.75Al0.25N and the Ga0.75Al0.25N with interstitial defects were calculated based on first principles. Results show that the band gap values of Ga0.75Al0.25N with interstitial defects are smaller than that of the pure Ga0.75Al0.25N. And Ga0.75Al0.25N crystals with Ga and Al interstitial defects show n-type property, meanwhile Ga0.75Al0.25N crystal with N interstitial defect show p-type property. The static dielectric constants of crystals with defects are much bigger than that of the pure one. And the metal reflective regions of the crystals shift to lower energy because of the interstitial defects.

As advanced semiconductor materials, GaN, AlN, and GaAlN alloys are widely used in optoelectronic devices. In order to research the optoelectronic properties of GaN, AlN, and Ga1−xAlxN with different Al component, models of GaN, Ga0.875Al0.125N, Ga0.750Al0.250N, Ga0.625Al0.375N, Ga0.500Al0.500N, and AlN were built, then the atomic structure, band structure, density of states, Mulliken charge distribution, and optical properties of the six crystals were calculated based on first principle calculations. Results show that the lattice parameters decrease while the band gap increases with the increase of Al component. The GaN, AlN, and GaAlN alloys are all semiconductors with direct band gap. The global transfer index increases with the increase of Al component. When the Al component is bigger and bigger, the absorption peak shifts to higher energy, and the threshold wavelength of Ga1−xAlxN decreases.

In0.53Ga0.47As is a new near-infrared material for negative electron affinity photocathodes. Geometry optimization combined generalized gradient approximation based on the density functional theory is adopted to calculate the bulk In0.53Ga0.47As. Lattice constant of bulk In0.53Ga0.47As after geometry optimization is compared with the theoretical one based on the Vigard law, which proves the reliability of the parameters of the geometry optimization. The energy bands, electronic structures and optical properties of the bulk ternary In0.53Ga0.47As for near-infrared photocathode are analyzed. Electron transition way which is closely related with the photoemission is analyzed from the energy bands and the density of electrons. The dielectric function and the optical absorption coefficient are made clear based on the partial density of states. It is found that optical absorption coefficient of bulk In0.53Ga0.47As is bigger than that of GaAs in the near-infrared band, which is in keeping with the experiments. The analysis provides a theoretical foundation to design a better near-infrared negative electron affinity photocathode from the point of microscopic atoms.

GaAs is a common material for negative electron affinity photoelectric cathodes. It has a widely application in night vision. It is unavoidable to produce point defects in the process of the GaAs growth. In this article, the first principle method is used to calculate the formation energy and the optical properties of six types familiar point defects in GaAs. Three types of point defects (Ga vacancy defect, As antisite defect and As interstitial defect) are easier to be formed in these six types according to the formation energy calculation. In fact, crystal GaAs is grown in an As-rich environment. The Ga vacancy, As antisite and As interstitial defects are easier to be formed in reality. Hence the theoretical calculation results are in keeping with the experiments. In this article, the optical properties of these three types are compared with that of perfect GaAs. The electron structures are changed as a result of the point defects. Some of the defect levels enter into the band gap and the electron transitions become easier. It makes the optical spectra move to the low-energy region. Additionally, GaAs with Ga vacancy defect and that with As interstitial defect shows similar optical properties. Therefore both of the two types of defects can be considered as the same in the later experiments. The theoretical results in this article provide the basis for experimental study for photoelectric emission of the real GaAs material related to the optical properties and electronic structures.

In order to compare optical properties of Wurtzite and zinc-blende Ga0.75Al0.25N and lay a foundation for preparation of Ga0.75Al0.25N photocathodes, absorption coefficient, complex refractive index, dielectric function, reflectivity and loss function of Ga0.75Al0.25N in two forms are calculated using first principle based on density functional theory. Results show that zinc-blende Ga0.75Al0.25N owns smaller band gap than Wurtzite Ga0.75Al0.25N, and its conduction band is more broad. The optical properties differences of two structures mainly occur at the range of 8.6–26.0 eV. The peaks of imaginary dielectric function and absorption curves are at higher energy point for zinc-blende Ga0.75Al0.25N. The highest absorption of Wurtzite Ga0.75Al0.25N is 351386.171/cm at 11.05 eV, which is smaller than zinc-blende of 437809.895/cm at 13.84 eV. The average reflectivity of Wurtzite Ga0.75Al0.25N is lower than that of zinc-blende Ga0.75Al0.25N. The results are conductive for designing component structures of Ga0.75Al0.25N photocathodes.

Based on first-principles plane-wave pseudopotential method, the band structure, density of state, E-Mulliken population and optical properties of vacancy defect Ga 0.5 Al 0.5 As are calculated. The influence of As vacancy on Ga electronic state is more obvious than on Al electronic state, the influence of Ga vacancy on As electronic state is more obvious than Al vacancy. The destruction caused by vacancy defects to Ga As sp 3 hybridized orbital is more serious than Al As sp 3 hybridized orbital. The influence of vacancies on the bonding structure, E-Mulliken population and charges are limited to the atoms nearby the vacancies. Ga vacancy and Al vacancy act as acceptor while As vacancy acts as donor. Ga 0.46875 Al 0.5 As owns most carries concentration and Ga 0.5 Al 0.5 As 0.96875 owns lest carries concentration. The influence of vacancy on optical properties is mainly in low energy range (0–12.5 eV) and is negligible in higher energy range. Influence of Ga vacancy and Al vacancy on optical properties is rather similar, which are obvious different from the influence of As vacancy on optical properties.

Using quantum mechanics GASTEP software package based on the first principle density function theory, the electronic structure and optical properties of Ga 1− x Al x As at different Al constituent are calculated. Result shows that with the increase of Al constituent, the band gap of Ga 1− x Al x As increases and varies from direct band gap to indirect band gap; the absorption band edge and the absorption peak move to high-energy side; the static reflectivity decreases. With the increasing of the incident photon energy, Ga 1− x Al x As shows metal reflective properties in certain energy range. With the increasing of Al constituent, static dielectric constant decreases and the intersection of dielectric function and the x -axis move towards high-energy side; the peak of energy loss function move to low-energy side and the peak value reduces.