The study explores the significance of band alignment at the intersection of HfZrO4 (HZO) and Ge-doped Ga2O3, offering insights pertinent to potential applications in high-power electronic devices due to its ferroelectric properties.
With the rise of advanced electronics, researchers have turned their attention to Ga2O3, known for its large bandgap of 4.8 eV and high breakdown voltage of 8 MV/cm. These traits make it attractive for ultraviolet (UV) optoelectronics and for applications like Schottky Barrier Diodes (SBDs) and field-effect transistors (FETs). Despite these advantages, Ga2O3 presents challenges as n-type doping is predominantly the only option, limiting its functionality.
Integriting ferroelectric materials like HZO, which has attracted attention for its efficient electrical properties and thermodynamic stability, could potentially improve Ga2O3-based devices by stabilizing the band alignment through ferroelectric polarization. The study focuses on HZO grown atop Ge-doped Ga2O3 films, employing hard X-ray photoelectron spectroscopy (HAXPES) to characterize the band alignment.
Utilizing High-resolution HAXPES, the researchers analyzed the interface performance under various bias conditions. The experiments aimed to measure band alignment and evaluate its dependency on applied bias. Initial results indicate challenges; charge injection and leakage current at the HZO/Ga2O3 interface hindered the stabilization of the expected ferroelectric polarization, with charge accumulating at the HZO/Ga2O3 interface once bias was applied.
High-resolution transmission electron microscopy (HRTEM) confirmed the structural integrity of the HZO film, affirming its polycrystalline nature with grain sizes between 5-10 nm. Structural digital-FFT analysis was employed to ascertain the material's orthorhombic phase. Interestingly, the expected ferroelectric behavior wasn't observed, largely due to dimensional changes caused by bias. While the HZO layer should exhibit polarization characteristics, the measurements indicated the absence of stable remanent polarization due to the effects of trapped charge within the layer.
Specifically, the findings revealed how the band alignment's dependency on applied bias led to significant shifts. Notably, Ti 2p emission showed shifts corresponding to bias, confirming the layer's good electrical contact. Conversely, the Ga 2p peaks indicated flat band conditions, demonstrating the highly conducting behavior of the Ge-doped Ga2O3.
According to the HAXPES data, the core level spectra exhibited asymmetries under bias conditions. The Hf 3d peaks demonstrated notable shifts, signaling the influence of band skewing. Importantly, under +5V bias, Hf 3d exhibited asymmetric peaks, moving as expected due to the applied voltage. On the contrary, when the bias is removed at 0V conditions, no polarization is retained, rather indicating dissipation of any injected charge within the HZO layer.
This charge trapping and the associated dynamics challenge the feasibility of integrating HZO with Ga2O3. Future steps will aim to investigate methods to optimize the ferroelectric properties of the HZO layer, enhancing stability and potentially mitigating leakage currents, thereby stabilizing ferroelectric characteristics at these interfaces.
Overall, this work provides fundamental insights and sets the groundwork for improving Ga2O3-based electronic devices by refining control over ferroelectric materials and their integration within higher performance systems.