Study on the Physical and Leakage Current Characteristics of an Optimized High-k/InAlAs MOS Capacitor with a HfO₂–Al₂O₃ Laminated Dielectric

High-k/n-InAlAs MOS capacitors are popular for the isolated gate of InAs/AlSb and InAlAs/InGaAs high-electron mobility transistors. In this study, a new kind of high-k/n-InAlAs MOS-capacitor with a HfO₂–Al₂O₃ laminated dielectric was successfully fabricated using an optimized process. Compared with the traditional HfO₂/n-InAlAs MOS capacitor, the new device has a larger equivalent oxide thickness. Two devices, with a HfO₂ (8 nm)–Al₂O₃ (4 nm) laminated dielectric and a HfO₂ (4 nm)–Al₂O₃ (8 nm) laminated dielectric, respectively, were studied in comparison to analyze the effect of the thickness ratios of HfO₂ and Al₂O₃ on the performance of the devices. It was found that the device with a HfO₂ (4 nm)–Al₂O₃ (8 nm) laminated dielectric showed a lower effective density of oxide charges, and an evidently higher conduction band offset, making its leakage current achieve a significantly low value below 10⁻⁷ A/cm² under a bias voltage from −3 to 2 V. It was demonstrated that the HfO₂–Al₂O₃ laminated dielectric with a HfO₂ thickness of 4 nm and an Al₂O₃ thickness of 8 nm improves the performance of the high-k dielectric on InAlAs, which is advantageous for further applications.