Project Angelica: Asymmetric Interface Architecture with Controlled Slippage for GaN-on-Si Heteroepitaxy (A Multi-Physics Co-Optimisation Framework for Next-Generation High-Electron-Mobility)

This paper presents Project Angelica — a novel buffer layer architecture for GaN-on-Si(111) heteroepitaxy based on a gadolinium oxide (Gd₂O₃) interlayer with asymmetric interface coupling. The core innovation lies in the deliberate engineering of two fundamentally distinct interface mechanisms: a Van der Waals weakly-coupled bottom interface (Si/Gd₂O₃) enabling atomic-scale controlled slippage, and a strongly-bonded covalent top interface (Gd₂O₃/GaN) providing a high-quality epitaxial template. Combined with a dense-to-dilute compositional grading profile — herein designated Angie's Grading — described by C(z) = (1−z)^α with α ≈ 0.10, and multi-objective optimization via Differential Evolution algorithm, the architecture achieves the following simulated results: Residual thermal stress reduced from 1110 MPa to 127.5 MPa (−88.5%) 2DEG sheet electron density increased 3.14× to 1.28×10¹³ cm⁻² AlGaN aluminum content safe limit extended from 7.3% to 22.9% Cut-off frequency fT = 116 GHz (Lg = 0.15 μm) Maximum oscillation frequency fmax = 147 GHz Noise figure NF = 0.51 dB at 28 GHz Estimated fatigue life: 2.7 million thermal cycles Maximum operating temperature: 350°C The architecture is directly compatible with existing MOCVD production equipment. Complete fabrication specifications, tolerance analysis, and simulation source code are provided to enable immediate laboratory validation by the research community. Keywords: GaN-on-Si, HEMT, heteroepitaxy, buffer layer, Gd₂O₃, rare-earth oxide, stress compensation, Van der Waals epitaxy, compositional grading, 2DEG, RF power amplifier, heterogeneous integrationVersion 2 updates the license from CC BY-NC 4.0 to CC BY 4.0 International (paper/documentation) + Apache License 2.0 (simulation source code). All content is now fully open. Version 3 update: Table 8 and Figure 6 corrected — power density values now reflect direct code output (16.5, 30.1, 368.6 W/mm) replacing earlier design estimates. Version 4 updates: (1) Added Appendix B — "Angie's Mixes": a generalised framework extending Angie's Grading to arbitrary interlayer material combinations and compositional grading strategies, including candidate material comparison (Eu₂O₃, La₂Zr₂O₇, Er₂O₃, Nd₂O₃, Y₂O₃, Pr₂O₃), Angie's Mixing Rule (solid-solution tuning via Vegard's Law), and the two-dimensional grading concept. (2) Clarified nomenclature: Angie's Grading (single-material concentration profile), Angie's Mixes (general framework), and Angie's Mixing Rule (mixed-material lattice tuning rule) are now formally defined.