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Many characterization and analytical instruments—particularly scanning electron microscopes—use electron detectors to examine sample surfaces. Low-energy electrons (< 1 keV) provide particularly valuable information about the texture and composition of the sample’s outermost atomic layers. However, the efficient detection of such electrons poses a technical challenge, as they penetrate only a few nanometers into the detector element and comparatively few detectable interactions occur.
In the eLGAD project, special low-gain avalanche detectors (LGADs) were therefore developed for low-energy electrons and light with shallow penetration depths. This type of detector incorporates an amplification zone directly within the semiconductor, which amplifies the weak background signals and thus makes even small signals measurable. The particular challenge lies in designing this amplification zone to be very thin (a few tens of nanometers deep). To this end, various acceptor dopants (boron, aluminum, gallium, indium, thallium) were investigated and analyzed for activation and stability. The fabricated detectors were subsequently electrically characterized. The results showed stable dark currents, a significant improvement due to guard ring designs, and a high quantum efficiency of up to 600%. Particularly in the low-energy range around 1 keV, an amplification of up to a factor of 21.5 was achieved. The project thus made significant progress in the development of surface-sensitive LGADs.