HAXPES of GaN  Interface in MOS High Electron Mobility Transistors

Surface Analysis Spotlight: XPS

by Kateryna Artyushkova


GaN-based high electron mobility transistors (HEMTs) are promising for the field of power electronics where higher switching frequency and reduced on-state resistance are required. The MOS-channel HEMT (MOSc-HEMT) ensures positive threshold voltage and minimizes gate current leakage thanks to its totally recessed AlGaN barrier and MOS gate. In the recent paper published in Power Electronic Devices and Components from our customers at CEA LETI, the impact of Al2O3 post-deposition anneal (PDA) deposited on etched GaN is investigated with electrical and chemical characterizations.

For chemical characterization, the authors used HAXPES available on the PHI Quantes system using a Cr high energy source. The XPS analysis of GaN-based semiconductor devices is challenging due to 1) the overlap between the N1s photoelectron line and Ga LMM Auger peak, and 2) the small sampling depth from which Ga 2p electrons originate - ~3 nm. By using a Cr source, both these obstacles can be overcome. The sampling depth increases to about 20 nm allowing analysis of interfaces below thicker gates oxide layers.

High-resolution Ga 2p and O 1s HAXPES spectra were used to analyze the chemical composition at the interface. There was oxidation of GaN at the interface, as shown by the Ga-O peak in Ga 2p spectrum. O 1s had contributions from O-Al and O-H species. As for gallium oxide, the presence of O-H groups was deduced from the area of O-H bonds in the O1s peak. “Ga-O bonds observed by HAXPES and related to the presence of interfacial gallium oxide (GaOX) reduce with PDA temperature until 500◦C and increase over 500◦C” as was shown in Figure 5 of the paper. OH groups also were reduced in Al2O3 with increasing PDA temperature. “The reduction of hysteresis with PDA temperature is attributed to GaOX reduction at the Al2O3/GaN interface.”

The beneficial reduction of hysteresis was correlated to the decrease in GaOX at the Al2O3/GaN interface and OH groups in the alumina.

Figure. HAXPES extracted chemical environments (Ga-O and O-H bonds) for different PDA temperatures and without final thermal budget. The take-off angle was 45◦ for Ga 2p3/2 and 90◦ for O1s analysis.

To learn more about the application of lab-based HAXPES to interfaces in semiconductor devices, please attend a talk by K. Artyushkova at TechConnect World 2023 conference, session “CHIPS: Advanced Metrology to Ensure Success for Next Generation Semiconductors” June 19-21, 2023. 

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