Strain-Engineered Wavelength Tuning in Flexible InGaN/GaN MQW LEDs via High-Modulus Tungsten Substrates

Abstract Reversible wavelength tuning in flexible inorganic light-emitting diodes (LEDs) is essential for emerging applications in strain-tunable micro-LED displays, adaptive color rendering, and wearable optical communication yet remains constrained by the limited strain-transfer efficiency of conventional polymer substrates. Here, we report a substrate-modulus engineering strategy that overcomes this limitation by integrating InGaN/GaN multiple-quantum-well (MQW) LEDs onto high-modulus tungsten (W) foils through Au–Sn eutectic wafer bonding and KrF excimer laser lift-off. The high Young’s modulus of W (411 GPa) positions the neutral mechanical plane (NMP) 76.81 μm above the substrate base, delivering a tensile strain of ε ≈ 4.21 × 10–3 at the MQW active region under a maximum curvature of 64.89 m–1 (R ≈ 15.4 mm), approximately 3 times that achievable with polyethylene terephthalate (PET) substrates. This amplified strain drives blueshifts of 11.39 nm (blue, 473.76 → 462.37 nm) and 15.45 nm (green, 509.98 → 494.53 nm) at 20 mA, accompanied by ∼10% enhancement in electroluminescence intensity, through partial relaxation of the quantum-confined Stark effect (QCSE). The 36% larger blueshift for the green emitter directly reflects its higher indium mole fraction (∼24% vs ∼17%), which strengthens intrinsic piezoelectric polarization and amplifies strain sensitivity. These results, exceeding prior polymer-based approaches by more than an order of magnitude, demonstrate that neutral-plane engineering through deliberate substrate-modulus selection provides a deterministic, nonthermal route to large-magnitude spectral control in flexible III-nitride emitters.