A Demonstration of Nitrogen Polar Gallium Nitride Current Aperture Vertical Electron Transistor

We report the first demonstration of Nitrogen polar (N-polar) GaN current aperture vertical electron transistor with a blocking electric field over 2.9 MV/cm. The devices were grown by metalorganic chemical vapor deposition on a c-plane sapphire substrate. The fabrication involved a maskless planar regrowth of a very thin-AlN layer above the current blocking layer, which induced a two-dimensional electron gas (2DEG) in the channel, and also prevented the out-diffusion of activated Mg ions into the GaN channel layer. The alloyed source and drain ohmic contacts on the regrown n + -GaN layer offered the low-contact resistance of 0.18 $\text{m}\Omega \cdot \text {cm}^{2}$ ( $0.22~\Omega \cdot \text {mm}$ ). The device displayed a maximum drain current of 1.68kA/cm 2 with a low R ON, SP of 2.48 $\text{m}\Omega \cdot \text {cm}^{2}$ . With just about 200 nm drift layer, a three-terminal breakdown voltage of 58 V was achieved. The output characteristics were free of dispersion under pulsed measurements with $80~\mu \text{s}$ and 500 ns pulse widths. The N-polar current aperture vertical electron transistors show fundamentally significant advantages in favor of using Mg 2+ -implanted GaN as current blocking layers compared with Ga-polar counterparts.