Aluminum Oxide at the Monolayer Limit via Oxidant-free Plasma-Assisted Atomic Layer Deposition on GaN

TL;DR

This paper demonstrates a method to create a continuous, pin-hole free aluminum oxide monolayer on GaN using plasma-assisted atomic layer deposition, enabling precise interface control for advanced semiconductor applications.

Contribution

It introduces a novel oxidant-free plasma-assisted ALD process to achieve ultrathin, continuous AlOx monolayers on GaN, overcoming traditional nucleation challenges.

Findings

Successfully encapsulated GaN with ~3 Å AlOx monolayer.

Modified surface properties, including decreased work function.

Achieved high-density self-assembled monolayers with near-theoretical limits.

Abstract

Atomic layer deposition (ALD) is an essential tool in semiconductor device fabrication that allows the growth of ultrathin and conformal films to precisely form heterostructures and tune interface properties. The self-limiting nature of the chemical reactions during ALD provides excellent control over the layer thickness. However, in contrast to idealized growth models, it is experimentally challenging to create continuous monolayers by ALD because surface inhomogeneities and precursor steric interactions result in island growth during film nucleation. Thus, the ability to create pin-hole free monolayers by ALD would offer new opportunities for controlling interfacial charge and mass transport in semiconductor devices, as well as for tailoring surface chemistry. Here, we report full encapsulation of c-plane gallium nitride (GaN) with an ultimately thin (~3 {\AA}) aluminum oxide (AlOx) monolayer, which is enabled by the partial conversion of the GaN surface oxide into AlOx using a combination of trimethylaluminum deposition and hydrogen plasma exposure. Introduction of monolayer AlOx significantly modifies the physical and chemical properties of the surface, decreasing the work function and introducing new chemical reactivity to the GaN surface. This tunable interfacial chemistry is highlighted by the reactivity of the modified surface with phosphonic acids under standard conditions, which results in self-assembled monolayers with densities approaching the theoretical limit. More broadly, the presented monolayer AlOx deposition scheme can be extended to other dielectrics and III-V-based semiconductors, with significant relevance for applications in optoelectronics, chemical sensing, and (photo)electrocatalysis.