(Invited) Understanding Plasma-Assisted Atomic Layer Epitaxy of InN and Opportunities for Collaboration through the Office of Naval Research Global
Authors: Eddy Charles Robert , Nepal Neeraj , Woodward Jeffrey , Myint Peco , Wang Chenyu , Zhang Xiaozhi , Wiegart Lutz , Fluerasu Andrei , Headrick Randall , Ludwig Karl 
Published: February 2024

The family of III-V nitride compound semiconductors has provided the foundation to a number of advanced electronic device technologies from light emitting diodes to radio frequency transistors to power switches. Of the family, binary indium nitride (InN) and ternaries/quaternaries containing InN have progressed at a slower pace due the material properties and related growth challenges. Having the weakest bonds in the family, the material has a lower melting point and more easily decomposes and phase separates (in ternaries and quaternaries). As such, a number of research efforts are looking for new growth approaches to overcome these challenges and realize the InN-based materials that will enable devices such has high speed switches and IR emitters and detectors.

To this end, plasma-assisted atomic layer epitaxy (PA-ALE) of InN and InN-containing ternaries has been explored in recent years. Much like atomic layer deposition, ALE consists of a sequence of self-limiting surface half-reactions that promotes “layer-by-layer” growth of films. The cyclical growth process starts with exposure of the growth surface first to the group III precursor (trimethylindium, for example), then purging excess precursor and reaction byproducts leaving only the ad-/physi-/chemi-sorbed species on the surface. After this purge, these surfaces are then exposed to a collection of plasma species (ions, radicals, neutrals, etc.) which reacts with the “sorbed” layer. The growth cycle is finished with a purge of the surface reaction by-products and unreacted plasma species before repeating. The potential of the process is based on the premise that by providing energy from plasma species to the growth surface, one can lower the temperature of growth to improve the stability of the material. Further, the reactive neutral plasma species also play a role by lowering activation energies for chemical reactions compared to thermal ALD, without necessarily providing energy to the growth surface.

A brief review of previous experimental demonstrations of epitaxial growth of InN and InN-containing ternaries will be presented showing the promise of the growth method to grow quality InN binary films and metastable ternaries containing InN not possible by conventional growth methods. For example, a metastable cubic phase of InN (NaCl) was realized as were ternary stoichiometries for both InAlN and InGaN that lie in the thermodynamic miscibility gap. Further, and in an effort to begin to understand this growth process and the role that plasma might play in growth mechanisms, synchrotron-based studies have been employed during growth of binary InN and digital InAlN and InGaN alloys. The results of these studies will be highlighted and key findings identified. Most recently, coherent x-ray scattering has been employed to provide additional insights including surface diffusion during each step of the cyclical growth process. The cumulative findings of these efforts will be presented, and future directions outlined.

As the presenting author is now detailed as a Science Director for Power & Energy and Advanced Materials to the U.S. Office of Naval Research Global in London, the last portion of the talk will be dedicated to introducing ONRG and its mission to engage international researchers through research grants, travel grants and conference support. The hope is to increase awareness of collaborative opportunities to the global research community expected to be in attendance.