Comparative study on characteristics of Si-based AlGaN/GaN recessed MIS-HEMTs with HfO2 and Al2O3 gate insulators.

Two types of enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with different gate insulators are fabricated on Si substrates. The HfO₂ gate insulator and the Al₂O₃ gate insulator each with a thickness of 30 nm are grown by the plasma-enhanced atomic layer deposition (PEALD). The energy band diagrams of two types of dielectric MIS-HEMTs are compared. The breakdown voltage (V_BR) of HfO₂ dielectric layer and Al₂O₃ dielectric layer are 9.4 V and 15.9 V, respectively. With the same barrier thickness, the transconductance of MIS-HEMT with HfO₂ is larger. The threshold voltage (V_th) of the HfO₂ and Al₂O₃ MIS-HEMT are 2.0 V and 2.4 V, respectively, when the barrier layer thickness is 0 nm. The C–V characteristics are in good agreement with the V_th's transfer characteristics. As the barrier layer becomes thinner, the drain current density decreases sharply. Due to the dielectric/AlGaN interface is very close to the channel, the scattering of interface states will lead the electron mobility to decrease. The current collapse and the R_on of Al₂O₃ MIS-HEMT are smaller at the maximum gate voltage. As Al₂O₃ has excellent thermal stability and chemical stability, the interface state density of Al₂O₃/AlGaN is less than that of HfO₂/AlGaN. [ABSTRACT FROM AUTHOR]