Determining and Mitigating Stoichiometry, Structural, and Mobility Degradation in Low-Temperature Grown GaN for Thin Film Transistors

Gallium nitride (GaN) is a promising channel material for back-end-of-line (BEOL) access transistors owing to its wide bandgap and high electron mobility, which together enable a high I on / I off current ratio and suppressed leakage. However, conventional metal organic chemical vapor deposition (MOCVD) growth requires temperatures above 1000 °C, exceeding BEOL thermal limits. Here, GaN growth across a wide reduced-temperature window is systematically investigated, revealing that mobility degradation is driven by compositional change arising from temperature-dependent precursor decomposition, while structural disorder evolves concurrently and defines distinct transport regimes at lower growth temperatures. At moderately reduced temperature, minor mobility degradation arises from subtle imperfections within the hexagonal phase, and nonideal chemical composition emerges as an important mobility-limiting factor. Upon further reduction to BEOL-compatible temperatures near 450 °C, a pronounced structural transition produces a mixed-phase microstructure of cubic nanograins embedded in an amorphous matrix, establishing an amorphous-dominated transport regime. Mobility degradation is mitigated through chemical composition control, growth−anneal super cycles, and buffer layer engineering. These findings provide a systematic framework for low-temperature GaN synthesis, potentially enabling its integration into monolithic three-dimensional (M3D) architectures under stringent thermal constraints.