Improvement of in-plane uniformity of cathodoluminescence from ZnO luminescent layers for electron beam excitation assisted optical microscope

We fabricated flat and homogeneous Al2O3/ZnO/Al2O3 heterostructure luminescent layers by atomic layer deposition (ALD) to serve as a nanometer-scaled light source for high-spatial-resolution optical microscopy based on electron beam excitation (EXA). A smooth surface was obtained by inserting an Al2O3 buffer layer and an Al2O3 barrier layer resulting in brighter and more uniform cathodoluminescence (CL) compared with that from a directly deposited ZnO layer. The root mean square (rms) value determined by atomic force microscope drastically decreased from 2.4 nm (for typical ZnO film) to 0.5 nm (for the six-layer pairs of the Al2O3/ZnO/Al2O3 heterostructure). The CL brightness increased by two times of that in the Al2O3/ZnO/Al2O3 heterostructure due to a waveguide effect. However, the increase in the number of the layer pairs from one to six reduced the CL brightness by half. The CL emission variability was about 30% improved that is supposed to enable high-resolution using Al2O3/ZnO/Al2O3 luminescent layers for an EXA microscope.