Electron beam-induced crystallization of Al2O3 gate layer on β-Ga2O3 MOS capacitors

•Electron irradiation crystallizes amorphous alumina films on beta-gallium oxide.•The electron dose rate is correlated to the crystallization rate.•The small lattice mismatch is favorable for the nucleation of crystallites.•Crystallization is driven by ionization-induced atomic rearrangement, not heating. Electron irradiation was observed to induce crystallization of amorphous Al2O3 films grown by atomic layer deposition on β-Ga2O3 substrates. Growth of large, strongly oriented crystalline γ-Al2O3 regions was induced using conventional-mode transmission electron microscopy (TEM) and observed to propagate outward from the interface as well as from the previously crystallized Al2O3. A few nm of epitaxial Al2O3 was already visible at the beginning of the crystallization front propagation. The phenomenon is not explained by electron beam-induced heating, which amounted to less than 1 K at all times. Direct measurement of the beam current permitted quantitative correlation between electron dose rates and crystallization rates. Enlarging the electron beam to reduce current density was found to slow the propagation of the crystallization front. Furthermore, a factor of 4 smaller electron dose was required for a given rate using 100 keV electrons as compared to 200 keV, indicating that crystallization is driven by ionization-induced atomic rearrangement within the gate layer. Lattice spacing between the oxygen sub-lattices of β-Ga2O3 and γ-Al2O3 are favorable for the nucleation of crystallites at the interface. Multivariate statistical analysis of electron energy loss spectroscopy (EELS) data also showed evidence of diffusion between Al and Ga in the substrates and gate oxides, respectively. These structural transformations at the semiconductor–insulator interface are expected to influence the device electrical behavior and are relevant to the continued refinement of β-Ga2O3 device technology.