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Jilin University achieves record 2DEG mobility for N-polar GaN/AlGaN heterostructures on SiC

1 d ago

**Jilin University achieves record 2DEG mobility for N-polar GaN/AlGaN HEMTs on SiC via MOCVD, boosting high-frequency millimeter-wave performance.** Researchers at Jilin University in China have reported a record two-dimensional electron gas (2DEG) mobility of 1947 cm²/V·s for nitrogen-polar (N-polar) GaN/AlGaN heterostructures grown on silicon carbide (SiC) substrates by metal-organic chemical vapor deposition (MOCVD) [Ma et al., *Appl. Phys. Lett.* 128, 072101 (2026)]. This is the highest value reported to date for N-polar GaN/AlGaN on SiC, addressing a key challenge in realizing high-performance N-polar GaN high-electron-mobility transistors (HEMTs) for W-band (75–110 GHz) applications, where output power densities up to 8 W/mm have been demonstrated. N-polar GaN HEMTs offer advantages over metal-polar devices but suffer from rough surface morphology and high oxygen impurity concentrations (~10¹⁸ cm⁻³) that degrade mobility via interface roughness and ionized impurity scattering. Led by Yuantao Zhang and Gaoqiang Deng, the team varied the growth temperature of the high-resistance GaN (HR-GaN) template layer between 950 °C and 1000 °C. Counterintuitively, lowering the temperature increased surface roughness (RMS from 2.94 nm to 4.32 nm) but improved 2DEG mobility from 1468 cm²/V·s to 1947 cm²/V·s. Secondary-ion mass spectrometry (SIMS) revealed that reducing the HR-GaN growth temperature increased carbon incorporation by an order of magnitude (from 1.1×10¹⁸ cm⁻³ to 1.1×10¹⁹ cm⁻³) while oxygen concentration dropped from 3.3×10¹⁷ cm⁻³ to 4.5×10¹⁶ cm⁻³. Under Ga-rich conditions, carbon preferentially occupies nitrogen sites, competitively suppressing oxygen incorporation. The reduced oxygen in the AlGaN barrier (from 2.1×10¹⁸ cm⁻³ to 2×10¹⁷ cm⁻³) weakens ionized impurity scattering—the dominant mobility-limiting mechanism. A semi-quantitative analysis using Matthiessen’s rule showed that a 10.5-fold suppression of ionized impurity scattering outweighs a 2.2-fold degradation from increased roughness. Device-level impact was verified: N-polar HEMTs with HR-GaN grown at 950 °C achieved full pinch-off at VGS = −2 V and a saturation current density of 492 mA/mm at VGS = 1 V, while devices grown at 1000 °C could not be fully pinched off due to buffer leakage. The higher carbon concentration also increased HR-GaN sheet resistance from 7.8×10⁵ Ω/sq to 9.1×10⁸ Ω/sq, suppressing leakage current. The team concludes this work provides an effective approach for enhancing 2DEG mobility in N-polar GaN/AlGaN heterostructures, advancing high-performance N-polar GaN HEMTs.