H2 based etching of GaN for re-grown gallium-free InAlN barriers giving very low 2DEG sheet resistance of 185 Ω/sq

Abstract

We have studied two approaches to GaN surface preparation before regrowth of InAlN layers, using Cl2 or H2 based etch conditions to prepare the wafer for barrier regrowth. We have shown that the Cl2 based etching induces layer degradation and higher sheet resistance values, while an H2 based etch, or desorption, does not degrade the surface morphology and yields improved sheet resistance. With additional optimization of the InAlN layers using this approach, increasing the growth temperature to 830 °C, we have achieved excellent sheet resistance values down to 185 Ohm/sq while maintaining gallium free growth. This regrowth optimization could equally be applied to AlGaN regrowth structures for normally off GaN based transistors.