Investigation of the cesium activation of Ga N photocathodes by low-energy electron microscopy
Year: 2024
Type: article
Abstract: Low-energy electron microscopy (LEEM) was performed on $p$-$\mathrm{Ga}\mathrm{N}$ samples during in situ cesium deposition. LEEM images of electron reflectivity recorded as a function of the incident electron energy at different $\mathrm{Cs}$ coverages allowed to spatially resolve the evolution of the local work function (WF) during the activation process. While the average WF drops by more than 3 eV, the local WF remains quite uniform across the surface throughout the activation process. Maximum fluctuations of less than 0.2 eV were observed in the WF maps for $\mathrm{Cs}$ coverage of a fraction of a monolayer. These fluctuations are mainly related to the surface topography, in particular, to the atomic steps' structure, which replicates the substrate miscut. Apart from these weak spatial fluctuations, no $\mathrm{Cs}$ clusters that would induce strong local WF contrast were observed at the scale of the 20-nm resolution of the measurements. These observations agree with the simple model of semiconductor activation to negative electron affinity that describes the formation of a dipole layer as responsible for the lowering of the WF. Additionally, at complete $\mathrm{Cs}$ coverage, the WF becomes fully homogeneous over the surface, smoothing out features originating from defects and topography.
Source: Physical Review Applied
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, Simons Foundation, Agence Nationale de la Recherche, Office of Science, Office of Energy Efficiency and Renewable Energy, University of California, Santa Barbara, Basic Energy Sciences, Solid State Lighting and Energy Electronics Center, University of California Santa Barbara, Office of Energy Efficiency, Core Research for Evolutional Science and Technology
Awards: G1286236842, G1286251239, G1798333901, G1863003419, G2293800358, G2618837358, G2710243964, G2758699378, G3021412113, G30714459, G3083819904, G419881185, G42916606, G4501827968, G498139845, RAISE-TAQS: The Hidden Structure of the Disorder in Quantum Systems, Theoretical, Experimental, and Computational Study of Carriers Localization in Nitride Devices, G5264466959, G5296751580, DE-EE0009691 UNIVERSITY OF CALIFORNIA AT SANTA BARBARA TITLED SOLUTIONS TO DROOP AND THE GREEN GAP BY NOVEL CARRIER INJECTION, G5613623313, G650090426, G6652958823, G835969469, G969889393
OpenAlex ID: W4402190601