An evaluation criterion and a design strategy for high-performance optical phase change materials in absorption-modulated integrated photonics

Phase change materials (PCMs) exhibit unique optical properties and have been widely used in various fields, such as optical memory, optical switches, and optical neuromorphic computing devices. However, owing to the lack of an evaluation criterion for assessing the optical performance of PCMs, the design of new PCMs mainly depends on empirical knowledge. Herein, a new evaluation criterion known as the material figure of merit (FOM₂ = Δk/k_amor) was introduced to assess the optical performance of PCMs in absorption-modulated integrated photonics. The FOM value represents the potential of PCMs in constructing high-performance PCM-based photonic devices. A higher FOM value indicates broader applicability of PCMs in photonic devices. To explore the relationships between the optical parameters of PCMs and the FOM value, three new optical PCMs based on Ge₂Sb₂Te₅ (GST) were developed according to the theory of optical bandgap. The results indicate that doping with non-metallic elements, such as nitrogen, increases the FOM₂ values of GST, which is beneficial for developing low-loss and high-modulation space absorption-modulated PCM-based photonic devices and large-scale absorption-modulated PCM-based photonic arrays. Additionally, the crystallization temperature of PCMs affects the programming power, endurance, and stability of the devices. Therefore, selecting suitable PCMs tailored to the specific requirements of the device in real-world applications is crucial. Our study provides an evaluation criterion for assessing the optical performance of PCMs, thereby facilitating the design of customized materials for photonic applications.