MOCVD growth of p-GaN-gated N-polar GaN HEMT heterostructures

This study investigates Mg-doped p-GaN gates integrated into N-polar GaN HEMT heterostructures grown by metal–organic chemical vapor deposition. Three epitaxial designs were compared to identify p-GaN growth temperatures and Al(Ga)N spacer designs (between the p-GaN and GaN channel) that suppress Mg back-diffusion into the GaN channel, as quantified by secondary ion mass spectrometry, while preserving the underlying two-dimensional electron gas (2DEG). A 2.7 nm Al0.27Ga0.73N spacer combined with 1020 °C p-GaN growth resulted in Mg pileup in the channel and a loss of measurable 2DEG conduction. In contrast, reduced Mg back-diffusion into the channel with preserved 2DEG transport was achieved through a 2 nm AlN spacer with 1020 °C p-GaN growth or a 2.7 nm Al0.27Ga0.73N spacer with 920 °C p-GaN growth. After selective removal of the p-GaN gate layer, Hall measurements yielded a 2DEG sheet density ns = 1.05 × 1013 cm−2 and 2DEG mobility μ = 730 cm2/V s for the AlN spacer with 1020 °C p-GaN growth sample, and ns = 1.58 × 1013 cm−2 and μ = 1344 cm2/V s for the Al0.27Ga0.73N spacer with 920 °C p-GaN growth sample. C–V measurements at 1 MHz further confirm functional p-GaN gating, with threshold voltages VTH ≈ −1.92 V for the AlN spacer with 1020 °C p-GaN growth sample and VTH ≈ −3.69 V for the Al0.27Ga0.73N spacer with 920 °C p-GaN growth sample. These results establish an epitaxial growth space for p-GaN-gated N-polar GaN HEMTs through spacer engineering and p-GaN growth-temperature control.