Probing the oxygen vacancy associated native defects in high-κ HfO2 using deep level transient spectroscopy

Abstract

Hafnium oxide (HfO2) has been explored as high-κ gate dielectrics in scaled CMOS devices, artificial synapses to be used in neuromorphic computing to achieve brain-like functionalities, a storage layer in memory devices, a piezoelectric energy harvester, and a photodetector. In this article, the origin of a native defect present in the HfO2 thin films on silicon is experimentally probed using deep level transient spectroscopy (DLTS) technique. It was realized that defects (predominantly oxygen vacancies) in HfO2 segregate near the Si/HfO2 interface. The interfacial and bulk HfO2 trap charges are communicating through the tunneling/ hopping, and, finally, they are emitted to the respective bands of silicon depending on the silicon used. We have observed four prominent defect states, and we believe that all these belong to oxygen vacancies in different charge states. The activation energies of trap states are in the range of 1.22–2.02 eV from the HfO2 conduction band edge, and they fall in front of the Si bandgap in the band alignment of the Al/HfO2/Si gate stack. The capture cross sections of these traps are measured with insufficient filling DLTS and found to be of the order of 10−19 cm2. The results provide valuable insights into realizing the behavior of oxygen vacancy-related deep defects in HfO2 and guide their possible impact on the device performance.