Lateral energy band engineering of Al2O3/III-nitride interfaces

In this work, we have used electrostatic engineering of the ALD dielectric/III-nitride interface to do lateral band engineering in a III-nitride HEMT. Due to challenges related to dopant activation and damage anneal, traditional ion implantation and diffusion techniques for lateral band engineering that are commonly used in other semiconductors, cannot be applied easily in the III-nitride system. We have developed an alternate method that uses surface fixed charges to engineer lateral energy band profiles, and used this to demonstrate an enhancement-mode AlGaN/GaN HEMT without any gate recess. Metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) based on the III-Nitride system can efficiently suppress gate leakage enabling lower gate-channel spacing for high frequency transistors, and low off-state leakage for power switching devices. Conventional normally-off MISHEMTs require precise etching control for recess gate [1] or heavy p+ doping for the junction gate [2]. However, plasma etching may induce variation of electrical characteristics caused by surface damage while p-doping can cause hysteresis. In this work, we show a new technique to achieve normally off AlGaN/GaN transistors. Our method exploits the interface properties of dielectric/III-nitride, where a high density of fixed charges of the order of 1 μC/cm² can be formed the interface of atomic layer deposited (ALD) dielectrics on GaN and AlN[3-5]. In this work, we use the combination of oxygen plasma and post metallization anneal (PMA) treatments to engineer the Al₂O₃/AlGaN (AlN) interface fixed charges. Based on this technology, lateral energy band engineering by patterning ALD Al₂O₃ is demonstrated. This technology provides a new approach to recess-free and doping-free normally-off MOSFETs /MISHEMTs.