Characterization of interface states in AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with HfO2 gate dielectric grown by atomic layer deposition

• Published in: Applied surface science Vol. 461; pp. 255 - 259
• Main Authors: Stoklas, R., Gregušová, D., Hasenöhrl, S., Brytavskyi, E., Ťapajna, M., Fröhlich, K., Haščík, Š., Gregor, M., Kuzmík, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-12-2018
• Subjects: ALD; AlGaN/GaN; HfO2 dielectric; Interface states; Water and ozone precursors; XPS analysis; HfO2 dielectric; ALD; Interface states; Water and ozone precursors; XPS analysis; AlGaN/GaN
• DOI: 10.1016/j.apsusc.2018.05.191
• EISSN: 1873-5584
• ISSN: 0169-4332

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•X-ray analysis of MOS-HFETs with HfO2 gate oxide prepared by ALD at two different precursors “water“ and “ozone“.•The gate leakage and RF current-collapse reduction of MOS-HFETs with HfO2 prepared by ozone-ALD compare with thermal-ALD.•The HfO2/AlGaN interface states reduction of MOS-HFET with ozone-ALD.
The impact of oxidation agent and post-metallization annealing (PMA) on the quality of oxide-semiconductor interface in AlGaN/GaN metal-oxide semiconductor heterostructure field-effect transistors (MOS-HFETs) with HfO2 grown by atomic layer deposition (ALD) was investigated. About six orders of magnitude lower gate leakage current (∼10−7 mA/mm at −10 V) was observed for MOS-HFETs with HfO2 gate oxide grown by ALD using ozone oxidation agent (O-HfO2), compared with grown using water oxidation agent (T-HfO2). In addition, the output current frequency dispersion was effectively reduced for O-HfO2 by applying PMA performed at 400 °C in N2 ambient, where the current frequency dispersion measured using 100 ns-long pulses was reduced from 40% for as-deposited gate oxide to only 10% for devices after applied PMA. Frequency dispersion was found to be consistent with density of oxide/semiconductor interface states (Dit) determined near the semiconductor conduction and valence band edge using the capacitance-voltage curves measured at different temperatures (CV-T) and photo-assisted capacitance transient (photo-C-t) technique, respectively. MOS-HFET structures with O-HfO2 showed about one order of magnitude lower Dit near the semiconductor valence band compared with structures with T-HfO2 (2 × 1011 compared with 1012 eV−1 cm−2 at EC-E = 2.5 eV, respectively). Moreover, for devices with O-HfO2, Dit was further reduced in entire energy gap as a result of PMA performed at 400 °C. The increased Dit for T-HfO2 oxides was attributed to Hf-Hf bonds at the HfO2/GaN interface, as deduced X-ray photoelectron spectroscopy (XPS) analysis. In contrast, formation of HfHf bonds was negligible in as-deposited O-HfO2 oxide films, while PMA at 400 °C led to reduction of the hydroxyl group observed by XPS.