Abstract
Microchannel plates (MCPs) are widely utilized as key device components in various photomultipliers; however, the performance of MCPs cannot be further improved by traditional processing. Atomic layer deposition (ALD) is a promising route to prepare a composite conductive layer and secondary electron emission (SEE) layer structure on the inner wall of the MCP. Moreover, ZnO is an essential component of a composite conductive layer, which is located at the bottom of the SEE layer and significantly influences the SEE coefficient, which, in turn, affects the gain performance of MCPs. Herein, ALD is used to deposit different thicknesses of ZnO films (1–50 nm) on an Si substrate, resulting in an ZnO/Si double-layer film structure. The relationship between the SEE coefficient and the primary electron energy of ZnO films with different thicknesses was established. The maximum secondary electron yield value of 2.04 is achieved at a film thickness of 30 nm. Moreover, Dionne's SEE model and theory of semiconductors are used to simulate and verify the experimental results. These results provide useful guidelines for the development of ALD-MCPs.
Highlights
Zinc oxide (ZnO) is an essential component of a composite conductive layer, which is located at the bottom of the secondary electron emission (SEE) layer and significantly influences the SEE coefficient, which, in turn, affects the gain performance of Microchannel plates (MCPs)
The current study provides an in-depth understanding of SEE characteristics of ZnO, an essential component of the conductive layer in MCPs
Owing to the self-limiting features of Atomic layer deposition (ALD), the film thickness can be precisely adjusted by controlling the number of ALD cycles
Summary
ALD (LabNano 9200, Ensure Scientific Group equipment) was used to deposit ZnO films on a single-crystal Si substrate with a diameter of 25.4 mm, crystal orientation of P/100, and a thickness of 525 μm. The substrate was placed in a reaction chamber with a high cavity. Zn(C2H5) and H2O reacted according to the following reactions and produced ALD-ZnO films on Si substrates: ÀOH*(g) þ Zn(C2H5)(g) ! During ALD-ZnO preparation, the reactants were purged in the given order: Zn(C2H5), N2, H2O, and N2. Both Zn (C2H5) and H2O were maintained at room temperature. The thickness of ALD-ZnO films was adjusted by controlling the number of ALD cycles. The thickness of ZnO films was varied from 10 to 500 Å by changing the ALD cycles from 5 to 250, respectively.
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