Improved device performance in <i>in situ</i> SiNx/AlN/GaN MIS-HEMTs with <i>ex situ</i> Al2O3 passivation at elevated temperatures

In the present work, the role of ex situ Al2O3 passivation in in situ SiNx/AlN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) to boost device performance and thermal stability during the high-temperature operations has been thoroughly investigated. At room temperature (RT), the MIS-HEMT fabricated with an atomic layer deposited (ALD)-Al2O3 (MIS-HEMT B) exhibits higher maximum drain current (Id,max), peak transconductance (gm,max), and lower subthreshold slope (SS) and gate leakage current compared to MIS-HEMT A fabricated without ex situ Al2O3, signifying the effectiveness of the ALD-Al2O3 layer to passivate severe surface states. Of note, when the temperature rises from 298 to 423 K, the values of Id,max and gm,max decrease noticeably, while SS and gate leakage current increase considerably in both MIS-HEMTs A and B. However, MIS-HEMT B demonstrates a lower degradation rate in various device properties at 423 K compared to MIS-HEMT A, implying that ALD-Al2O3 passivation improves thermal stability. Additionally, ALD-Al2O3 passivation reduces the interface state density from 7.48 × 1012 to 5.3 × 1012 cm−2 eV−1, highlighting its critical role in improving overall device performance.