Speaker
Description
Ultrathin (1-4 nm) films of wide-bandgap semiconductors play a vital role in numerous microelectronics application. However, the properties of these films can be significantly influenced by defects, particularly those originating from the interface between the substrate and the film. Motivated by this, an in vacuo atomic layer deposition (ALD) was developed for synthesis of ultra-thin Ga$_2$O$_3$/Al$_2$O$_3$ atomic layer stacks (ALS) on Al electrode. It is found that the Ga$_2$O$_3$/Al$_2$O$_3$ ALS can form an interface with the Al electrode with negligible interfacial defects under the optimal ALD condition whether the starting atomic layer is Ga$_2$O$_3$ or Al$_2$O$_3$. This interface is crucial for attaining an optimal and adjustable electronic structure and dielectric characteristic in the ultrathin Ga$_2$O$_3$/Al$_2$O$_3$ ALS. In-situ scanning tunneling spectroscopy (STS) confirms that the electronic structure of Ga$_2$O$_3$/Al$_2$O$_3$ ALS can have tunable bandgaps ($E_g$) between $\sim 2.0$ eV for $100\%$ Ga$_2$O$_3$ to $\sim 3.4$ eV for $100\%$ Al$_2$O$_3$, which agrees with DFT calculations. These bandgaps exhibit significant non-linearity as a function of Al concentration. Furthermore, the dielectric constant $\varepsilon$ of ultrathin Ga$_2$O$_3$/Al$_2$O$_3$ ALS capacitors is tunable through variation of the constituent Ga$_2$O$_3$ and Al$_2$O$_3$ atomic layer numbers from 9.83 for 100% Ga$_2$O$_3$ to 8.28 for $100\%$ Al$_2$O$_3$.
