Improved thermal stability and electrical properties of atomic layer deposited HfO2/AlN high-k gate dielectric stacks on GaAs

Abstract

The thermal stability and electrical properties of atomic layer deposited HfO2/AlN high-k gate dielectric stacks on GaAs were investigated. Compared to HfO2/Al2O3 gate dielectric, significant improvements in interfacial quality as well as electrical characteristics after postdeposition annealing are confirmed by constructing HfO2/AlN dielectric stacks. The chemical states were carefully explored by the x-ray photoelectron spectroscopy, which indicates the AlN layers effectively prevent from the formation of defective native oxides at elevated temperatures. In addition, it is found that NH3 plasma during AlN plasma-enhanced atomic layer deposition also has the self-cleaning effect as Al(CH3)3 in removing native oxides. The passivating AlN layers suppress the formation of interfacial oxide and trap charge, leading to the decrease of capacitance equivalent thickness after annealing. Moreover, HfO2/AlN/GaAs sample has a much lower leakage current density of 2.23 × 10−4 A/cm2 than HfO2/Al2O3/GaAs sample of 2.58 × 10−2 A/cm2. For the HfO2/AlN/GaAs sample annealed at 500 °C, it has a lowest interface trap density value of 2.11 × 1011 eV−1 cm−2. These results indicate that adopting HfO2/AlN dielectric stacks may be a promising approach for the realization of high quality GaAs-based transistor devices.