Cs and Cs/O adsorption mechanism on GaN nanowires photocathode

Xia, Sihao; Liu, Lei; Diao, Yu; Kong, Yike

doi:10.1007/s10853-017-0801-7

Cited by 30 publications

(13 citation statements)

References 33 publications

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“…Cs‐activated GaN photocathode has been applied in flame detection, 1 corona detection, 2 ultraviolet communication, 3 and other fields. Because Cs activation plays an important role in reducing surface barrier and work function, it helps the photocathode achieve a negative electron affinity state which is beneficial to photoelectron emission 4 . In recent years, there are many theoretical and experimental studies on Cs‐absorbed GaN surface reported successively.…”

Section: Introductionmentioning

confidence: 99%

“…Because Cs activation plays an important role in reducing surface barrier and work function, it helps the photocathode achieve a negative electron affinity state which is beneficial to photoelectron emission. 4 In recent years, there are many theoretical and experimental studies on Cs-absorbed GaN surface reported successively. The GaN photocathode prepared by Machuca et al 5 had a quantum efficiency (QE) of 50% at 310 nm after Cs activation.…”

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confidence: 99%

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Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Liu

2021

Int J Energy Res

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A negative electron affinity photocathode can be obtained by adsorbing Cs on the emission layer surface of photocathode, which greatly improves the number of electrons escaped and the quantum efficiency. Based on first principles, this paper studies the structural and electronic properties of Cs-adsorbed GaN monolayer and bilayer. The results reveal that the Cs-adsorbed GaN monolayer is the most stable when Cs atom is adsorbed at T Ga site. There is a significant charge transfer between Cs atom and GaN monolayer, and the difference in electronegativity makes electrons of Cs atom transfer to GaN monolayer system. Cs adsorption can reduce band gap, work function, and electron affinity, which is conducive to the escape of electrons and improvement of quantum efficiency. Cs adsorption is helpful for tuning optical properties of GaN monolayer. For the GaN bilayer, greater stability and lower work function make the Cs adsorbed above the top layer of GaN bilayer be more beneficial to the improvement of photoelectric performance. Novelty StatementBased on first principles, this paper studies the structure and electric properties of Cs-adsorbed GaN monolayer and bilayer. Cs adsorption can reduce band gap, work function, and electron affinity, which is conducive to the escape of electrons and improvement of quantum efficiency. And for the GaN bilayer, greater stability and lower work function make the Cs adsorbed above the top layer of GaN bilayer be more beneficial to the improvement of photoelectric performance. K E Y W O R D Scharge transfer, Cs adsorption, first principles, GaN bilayer, GaN monolayer | INTRODUCTIONCs-activated GaN photocathode has been applied in flame detection, 1 corona detection, 2 ultraviolet communication, 3 and other fields. Because Cs activation plays an important role in reducing surface barrier and work function, it helps the photocathode achieve a negative electron affinity state which is beneficial to photoelectron emission. 4 In recent years, there are many theoretical and experimental studies on Cs-absorbed GaN surface reported successively. The GaN photocathode prepared by Machuca et al. 5 had a quantum efficiency (QE) of 50% at 310 nm after Cs activation. Norton et al 6 achieved a high-quality GaN emission layer with 40% QE at 185 nm by using Cs treatment. Du et al 7 discussed the adsorption mechanism of Cs based on first principles and showed that Cs adsorption can reduce

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Liu

2021

Int J Energy Res

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“…However, when Cs coverage is over 1/2 ML, the average work function of Cs‐adsorbed surfaces exhibits an elevating trend. This phenomenon is called as “Cs‐kill,” which is often observed in the surface Cs activation experiments of semiconductor materials 38,39 . The Model 17 with three Cs atoms, respectively, located at T Si1 , B Si2 ′, H 1 sites achieves the lowest work function (0.92 eV), which is extremely approaching to the work function of P‐doped diamond films (0.9 eV) 12 .…”

Section: Resultsmentioning

confidence: 95%

“…This phenomenon is called as "Cs-kill," which is often observed in the surface Cs activation experiments of semiconductor materials. 38,39 The Model 17 with three Cs atoms, respectively, located at T Si1 , B Si2 0 , H 1 sites achieves the lowest work function (0.92 eV), which is extremely approaching to the work function of P-doped diamond films (0.9 eV). 12 Based on the results of Yang et al, 2 the maximum conversion efficiency of PETE devices with anode material of 0.92 eV can reach 30%.…”

Section: Multiple Cs Atoms Adsorptionmentioning

confidence: 94%

Exploring n‐type SiC film with ultralow work function Cs coating surface for solar cell anode

2021

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In this study, the Cs adsorption behavior on n-type 3C-SiC (0001)-(2 × 1) and-(3 × 2) reconstructed surfaces are investigated via first-principles calculations. The potentiality of 3C-SiC as the anode material of solar cell based on photonenhanced thermionic emission (PETE) is discussed. Various doping configurations are considered for the determination of an optimum n-type doping structure. Cs-covered (3 × 2) surface exhibits stronger stability compared with (2 × 1) surface. The charge transfer caused by Cs adsorption produces a [Cs +-SiC] dipole moment directing from Cs adatom to reconstructed surface, resulting in an effective declination of work function. Specifically, 0.5 ML Cs coverage surface provides an ultralow work function with 0.9 eV, demonstrating its potential application in PETE devices. Combining with a photoemission model, the maximum conversion efficiency can attain 30% utilizing SiC as an anode. Moreover, the Mulliken charge analysis provides the details of surface charge transfer and implies the inner mechanism of work function alteration. This study provides guiding significance for the synthesis of SiC material with low work function and an effective theoretical method for the design of highperformance anode materials in application of PETE devices. The adsorption mechanism of Cs on n-type doped 3C-SiC(0001)-(2 × 1) and-(3 × 2) reconstructed surfaces and its application as the anode material of solar cell are systematically investigated. For one Cs adatom adsorption, Cs-covered (3 × 2) surfaces present stronger stability compared with (2 × 1) surfaces. Csdecorated (3 × 2) surface with 0.5 ML coverage exhibits an ultralow work function as low as 0.9 eV. Based on the photoemission model, the maximum conversion efficiency of PETE devices with SiC anode can reach 30%. Highlights • Cs-decorated SiC surfaces with ultralow work function are suitable as PETE anode materials. • Cs adsorption mechanism on 3C-SiC(0001)-(2 × 1) and-(3 × 2) surfaces are explored. • The optimum n-type doped (2 × 1) and (3 × 2) surfaces are, respectively, determined.

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“…29,30 For GaAs photocathodes within external electric filed, polarization is much more adequate than that of the conventional NEA GaAs electron source. 31 Based on the fact that new low-dimensional materials have been widely used in optoelectronic devices, 32,33 here, we mainly study the effect of electron-trapping ability of nanowire photocathodes under external electric field. In order to comparison of the QE and polarization of the field-assisted cathodes with or without build-in field, we obtain carrier concentrations using the diffusion-drift formula.…”

Section: Introductionmentioning

confidence: 99%

Comparison of quantum and collection efficiency of field‐assisted uniform‐doping and exponential‐doping GaN nanowire cathodes

Liu

2020

Int J Energy Res

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Summary The field‐assisted method is proposed to increase electron capture of the GaN nanowire cathode. We deduce the photoemission or electron collection efficiencies of the field‐assisted uniform‐doping and exponential‐doping cathodes using the diffusion‐drift formula. Results show that the external electric field has a significantly better collection efficiency for uniform‐doping nanowire cathodes than that of exponential‐doping. In cathodes without a build‐in field, quantum efficiency and collection efficiency reached a maximum at incident angles of 65° and 45°, and field intensity of 0.1 and 0.7 V/μm, respectively. The external electric field also contributes to the polarization of GaN nanowires. The field‐assisted GaN NWAs (nanowirearray) cathode could improve the photoemission performance and are expected to be realized in the follow‐up experiment.

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Cs and Cs/O adsorption mechanism on GaN nanowires photocathode

Cited by 30 publications

References 33 publications

Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Exploring n‐type SiC film with ultralow work function Cs coating surface for solar cell anode

Comparison of quantum and collection efficiency of field‐assisted uniform‐doping and exponential‐doping GaN nanowire cathodes

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