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

(Al_xGa_1–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)-(Al_xGa_1–x)₂O₃ films have been studied, the recent availability of (100), ((Formula presented.) 01)-Ga₂O₃ substrates have developed interest in (100), ((Formula presented.) 01)-(Al_xGa_1–x)₂O₃ films. In this work, an investigation of microscopic and spectroscopic characteristics of (100), ((Formula presented.) 01), (010)–(Al_xGa_1–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)–(Al_xGa_1–x)₂O₃ films attributed to their spectroscopic properties. The study expanded APT's capabilities to determine Ga─O and Al─O 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 Ga─O and Al─O bonding energy has an inverse relationship with their bond length as crystallographic orientations vary. This systematic study of growth orientation dependence of (Al_xGa_1–x)₂O₃ films’ microscopic and spectroscopic properties will guide the development of new (100) and ((Formula presented.) 01)-(Al_xGa_1–x)₂O₃ along with existing (010)–(Al_xGa_1–x)₂O₃ films.