In situ surface study of the activating layer on GaAs (Cs, O) photocathodes

Rodway, D. C.; Allenson, M.B.

doi:10.1088/0022-3727/19/7/024

Cited by 44 publications

(14 citation statements)

References 31 publications

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“…During the activation process, a monolayer of CsO is deposited on the surface of the semiconductor, lowering its work function and establishing NEA. [3][4][5] This allows for high quantum efficiency ͑QE͒ ͑the ratio of electrons emitted to photons illuminating the cathode surface͒ of photoemission over the entire range of visible light. 6 However, this layer is extremely sensitive to contamination, which destroys the NEA properties of the surface and reduces its QE.…”

Section: Introductionmentioning

confidence: 99%

Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system

Sen

1998

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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Negative electron affinity photocathodes may have useful applications as electron sources for high-throughput microlithography [A. Baum et al., J. Vac. Sci. Technol. B 15, 2707 (1997)]. However, the nature of such a system has raised questions about the lifetime and reliability of a cathode during operation. In this article, we report on the lifetime and reliability of cathode operation under various conditions applicable to lithography. To perform these measurements, a 632 nm laser was focused onto a spot smaller than 10 μm in diameter on the back surface of the cathode (active area 0.5–2.0 μm thick). The emitted electrons were accelerated to 5 kV to form a magnified image of the cathode on a phosphor screen 1 m away. The 1/e lifetime of the cathode was measured as a function of the cathode current, which turned out to be an inverse relationship. Additionally, a wafer coated with SAL-601 resist was substituted for the phosphor screen to determine if resist outgassing induced by exposure affected operating lifetime. It was found that the cathode had a lifetime (75 h at 165 nA) that was the same as that obtained without the wafer under similar conditions. Lifetime was also found to be a function of initial level of cesiation of the surface and cesium levels during activation. In particular, when the cathode was initially overcesiated, the Faraday cup current (in the plane of the phosphor) was found to be stable to 2% for up to 3 days at 200 nA, indicating that the cesium level that optimizes lifetime is not necessarily the same level that optimizes quantum efficiency.

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Section: Introductionmentioning

confidence: 99%

Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system

Sen

1998

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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“…Until the photocurrent peak no longer increased, the O source and Cs source were closed successively, and the activation process was finished. To further improve the photoemission performance, the second heat treatment with a lower temperature was employed to the samples [36]. After that, the samples were activated again using the same co-deposition activation.…”

Section: Activation Of Photocathode Surfacementioning

confidence: 99%

Energy Bandgap Engineering of Transmission-Mode AlGaAs/GaAs Photocathode

Zhang¹,

Jiao²

2018

Photodetectors [Working Title]

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Aiming to enhance the photoemission capability in the waveband region of interest, a graded bandgap structure was applied to the conventional transmission-mode AlGaAs/ GaAs photocathodes based on energy bandgap engineering, wherein the composition in Al x Ga 1Àx As window layer and the doping concentration in GaAs active layer were gradual. According to Spicer's three-step model, a photoemission theoretical model applicable to the novel transmission-mode Al x Ga 1Àx As/GaAs photocathodes was deduced so as to guide the cathode structural design. Then the cathode material was grown by the metalorganic chemical vapor deposition technique, and the epitaxial cathode material quality was evaluated by the means of scanning electron microscope, electrochemical capacitance-voltage, X-ray diffraction and spectrophotometry. Through a series of specific processes, the cathode material was made into the multilayered module, possessing a glass/Si 3 N 4 /Al x Ga 1Àx As/GaAs structure. After the surface treatment including heat cleaning and Cs▬O activation for the cathode module, the image intensifier tube comprising the activated cathode module, microchannel plate, and phosphor screen was fabricated by indium sealing. The spectral response test results confirm the validity of the novel structure for the enhancement of blue-green photoresponse.

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“…The photocurrent of AlGaAs sample reaches at a peak of 3.41µA at the time of 29 min when the Cs coverage rise at 0.75 ML, while the photocurrent of AlGaN sample achieves a peak of 0.57µA at the time of 30 min when the Cs coverage rise at 0.5 ML. After the maximum value, the photocurrent decreases with the increasing Cs coverage, which called "Cs killer" phenomenon [10,33,34]. Chen et al [35] shows that the photocurrent is inversely proportional to the work function, in other words, it indicates that with Cs coverage increasing, the photocurrent increases and when it reaches at a peak, the work function decreases to a minimum value and then increases again.…”

Section: ) Photocurrentmentioning

confidence: 99%

Comparative Research on Cs Activation Mechanism for Al0.5Ga0.5As (001) and Al0.25Ga0.75N (0001) Surface

Shen

Chen

et al. 2015

IEEE Sensors J.

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To investigate and distinguish the difference of Cs activation mechanism on Al 0.5 Ga 0.5 As (001) and Al 0.25 Ga 0.75 N (0001) surface, plane wave with ultrasoft pseudopotential method based on first-principle density functional theory (DFT) is used. Surface adsorption energy, work function and surface dipole moments with different Cs coverage are calculated and compared. Eight possible Cs adsorption sites are chosen for the Al 0.5 Ga 0.5 As (001) surface while seven high-symmetry sites are considered in the calculation model of Al 0.25 Ga 0.75 N (0001) surface. Results show that when only one Cs atom adsorbed on two surfaces, the adsorption energies are all negative and the adsorption sites are all stable sites. The lowest work function and the most stable adsorption sites with different Cs coverage are obtained and discussed. When different amounts of Cs atoms adsorbed on two surfaces, the work function values of Al 0.25 Ga 0.75 N (0001) surface are all smaller than that of Al 0.5 Ga 0.5 As (001) surface. The work function of Al 0.5 Ga 0.5 As (001) surface decreases with the increase of Cs coverage when the Cs coverage changes from 0 monolayer (ML) to 0.75 ML, while Al 0.25 Ga 0.75 N (0001) surface achieves the smallest work function when the Cs coverage is 0.5 ML. Finally, photocurrent curves during Cs activation are recorded. The photocurrent of AlGaAs sample reaches at a peak at the time of 29 min when the Cs coverage rise at 0.75 ML, while the photocurrent of AlGaN sample achieves a peak at the time of 30 min when the Cs coverage rise at 0.5 ML, which is in well consistent with our calculation results.

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In situ surface study of the activating layer on GaAs (Cs, O) photocathodes

Cited by 44 publications

References 31 publications

Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system

Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system

Energy Bandgap Engineering of Transmission-Mode AlGaAs/GaAs Photocathode

Comparative Research on Cs Activation Mechanism for Al<sub>0.5</sub>Ga<sub>0.5</sub>As (001) and Al<sub>0.25</sub>Ga<sub>0.75</sub>N (0001) Surface

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