| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Friday Sessions |
| Session TF-FrM |
| Session: | Theory and Characterization of Thin Film Properties |
| Presenter: | John (Jack) Lyons, U.S. Naval Research Laboratory |
| Authors: | J. Lyons, U.S. Naval Research Laboratory S.C. Erwin, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
The management of unwanted impurities as well as the controlled introduction of dopant species continue to be challenges in wide-band-gap (WBG) semiconductors such as AlN and Ga2O3. In these materials, contaminants such as carbon often incorporate during growth and subsequently act as trapping centers, which can have a detrimental impact on device performance. Moreover, establishing hole conductivity through the introduction of acceptor impurities has proven to be especially difficult in these compounds. In this talk, I will discuss the use of first-principles calculations to understand the incorporation and electronic properties of impurities in WBG semiconductors.
In many growth techniques carbon-containing precursors, such as trimethylaluminum (TMA) for AlN, are often employed. These precursors are thought to be a major source of carbon contamination during growth. Focusing on atomic-layer deposition, we have developed a model to elucidate the decomposition of TMA at the AlN surface, and subsequent incorporation of carbon into the AlN film during growth. We find that the use of H-containing plasma is crucial for scrubbing methyl species from the surface. However, the plasma also leads to atomic carbon, which opens a channel for trapping carbon impurities into the film. In light of this dual role, we propose a solution for minimizing carbon contamination into AlN.
Quantitative determination of the electrical role of particular impurity species present within WBG semiconductors has long been a challenge for theoretical calculations. However, using hybrid density functional theory we are now able to accurately predict the role of impurities such as carbon. We find that carbon acts predominantly as a deep acceptor trap in AlN, as it does for GaN. In contrast, carbon is found to act as a donor species in WBG oxides such as Ga2O3. Other potential acceptor dopants, such as magnesium, are also found to act as deep acceptors, due to their propensity to trap localized holes. In fact, no acceptors are found to be effective p-type dopants in either Ga2O3 or AlN. However, acceptor dopants are still found to be useful for producing semi-insulating material.