Microscopic and Spectroscopic Investigation of (AlxGa1-X)2O3 Films: Unraveling the Impact of Growth Orientation and Aluminum Content

(AlxGa1-x)2O3 is an ultrawide-bandgap semiconductor with a high critical electric field for next-generation high-power transistors and deep-ultraviolet photodetectors. While (010)-(AlxGa1-x)2O3 films have been studied, the recent availability of (100), (2 over bar $\bar 2$01)-Ga2O3 substrates have developed interest in (100), (2 over bar $\bar 2$01)-(AlxGa1-x)2O3 films. In this work, an investigation of microscopic and spectroscopic characteristics of (100), (2 over bar $\bar 2$01), (010)-(AlxGa1-x)2O3 films is conducted. A combination of scanning transmission electron microscopy, atom probe tomography (APT), and first-principle calculations (DFT) is performed. The findings reveal consistent in-plane chemical homogeneity in lower aluminum content (x = 0.2) films. However, higher aluminum content (x = 0.5), showed inhomogeneity in (100), (010)-(AlxGa1-x)2O3 films attributed to their spectroscopic properties. The study expanded APT's capabilities to determine GaO and AlO bond lengths by mapping their ion-pair separations in detector space. The change in ion-pair separations is consistent with varying orientations, irrespective of aluminum content. DFT also demonstrated a similar trend, concluding that GaO and AlO bonding energy has an inverse relationship with their bond length as crystallographic orientations vary. This systematic study of growth orientation dependence of (AlxGa1-x)2O3 films' microscopic and spectroscopic properties will guide the development of new (100) and (2 over bar $\bar 2$01)-(AlxGa1-x)2O3 along with existing (010)-(AlxGa1-x)2O3 films. The figure depicts a comprehensive analysis of structure-property relationships in (AlxGa1-x)2O3 films oriented along (100), (2 over bar $\bar 2$01), and (010) directions. Leveraging Atom Probe Tomography, novel insights into GaO and AlO bond lengths are attained through the extraction of ion-pair separations in detector space and their dependence on varying crystal orientations. image