Abstract
HfO2/AlGaN/GaN metal–insulator–semiconductor (MIS)-type high electron mobility transistors (HEMTs) on Si substrates were fabricated by atomic layer deposition of HfO2 layers and post-deposition annealing (PDA). The current–voltage characteristics of the MIS-HEMTs with as-deposited HfO2 layers showed a low gate leakage current (Ig) despite the relatively low band gap of HfO2, and a dynamic threshold voltage shift (ΔVth) was observed. After PDA above 500 °C, ΔVth was reduced from 2.9 to 0.7 V with an increase in Ig from 2.2 × 10−7 to 4.8 × 10−2 mA mm−1. Effects of the PDA on the HfO2 layer and the HfO2/AlGaN interface were investigated by x-ray photoelectron spectroscopy (XPS) using synchrotron radiation. XPS data showed that oxygen vacancies exist in the as-deposited HfO2 layers and they disappeared with an increase in the PDA temperature. These results indicate that the deep electron traps that cause ΔVth are related to the oxygen vacancies in the HfO2 layers.
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