InP/LiNbO3 Covalent Heterointerface Construction via an Asymmetric Plasma Activation Strategy for Hybrid Integrated Quantum Systems

Lithium niobate (LiNbO₃) is emerging as an appealing candidate for integrated optical applications with enhanced complexity, owing to its inherent abundant optoelectronic properties. To compensate for the inability of LiNbO₃ to generate indistinguishable single photons, the evanescent coupling heterointerface constructed between III-V compound semiconductors (e.g., InP) and LiNbO₃ through plasma activation provides a feasible solution for balancing the integration efficiency and interfacial stability while achieving sub-50 nm alignment accuracy between devices, thus offering ultracompact on-chip light sources for classical optoelectronics and quantum optics. However, a challenge remains in the formation of the InP/LiNbO₃ platform due to the huge mismatch in the coefficient of thermal expansion. Here, we demonstrate the InP/LiNbO₃ covalent heterointerface using an asymmetric plasma activation strategy. Different plasmas are used for the activation of InP and LiNbO₃ specifically, balancing the enhancement of surface functional group density with the avoidance of defect generation effectively. More importantly, combined with surface comprehensive characterizations and interface performance, we determine that the introduction of ammonia solution enables the surface hydroxyl groups to be "effective" as LiNbO₃ surface relaxation increases the chance of -OH groups' contact. Therefore, a robust covalent bond network is established across the InP/LiNbO₃ interface at 80 °C with an enhanced bonding strength of 9.7 MPa. Moreover, a hybrid quantum photonic chip based on the InP/LiNbO₃ platform is designed to compute the coupling efficiency and the impact of misalignment on it, demonstrating the potential of extending the platform to hybrid integrated quantum systems.