| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuM |
| Session: | Interfaces in Multilayers & Nanocomposites |
| Presenter: | Virginia Anderson, US Naval Research Laboratory |
| Authors: | N. Nepal, US Naval Research Laboratory V.R. Anderson, US Naval Research Laboratory J.K. Hite, US Naval Research Laboratory C.R. Eddy, Jr., US Naval Research Laboratory |
| Correspondent: | Click to Email |
Aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN) semiconductors and their corresponding ternary films, such as InGaN, offer attractive properties, with high breakdown fields and widely tunable direct band gaps. Currently, III-nitrides are primarily deposited with molecular beam epitaxy and chemical vapor deposition. The addition of Atomic Layer Epitaxy (ALE) to the possible growth techniques is driven by the need for ever thinner films integrated into complex heterostructures, something that is increasingly difficult to achieve by conventional techniques. Furthering the attraction of ALE is the promise of lower growth temperatures that allow the deposition of a wider range of indium containing ternary films.
Here we report on ALE in a plasma-equipped Ultratech/Cambridge Nanotech atomic layer deposition system to grow AlN, GaN, and InN at temperatures significantly lower than needed for molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD).[1] In growing epitaxial materials, the substrates and corresponding surface preparation procedures are important. The substrates include silicon(111), sapphire, and MOCVD gallium nitride on sapphire, as well as graphene.[2]
For InN on a-plane sapphire, the expected wurtzite hexagonal phase was heteroepitaxially grown for films deposited in the temperature window of 220 to 260 C, well below the typical minimum 450 C temperature used in MOCVD. At an even lower temperature, 183 C, the heteroepitaxial InN on a-plane sapphire was discovered to be cubic phase with a NaCl structure, a phase of InN that had before been unreported.[3] Heteroepitaxial AlN films were grown on GaN/sapphire at a much lower temperature (500 C) than by MOCVD, typically 1100 C or more. Finally, GaN has been included in ALE deposited ternaries in the relatively low temperature window of 250-400 C even as its optimization continues. The ALE grown III-N films have carbon and oxygen contamination that hinders their immediate use in many applications, and improving the film purity is a major focus. In addition, initial deposition of indium ternaries indicates that more stoichiometries are available by ALE than MOCVD.
The possibilities for greater use of III-nitrides are apparent even at the early stages of progress in atomic layer epitaxy. Further characterization during and after deposition of the films should lead to materials suitable for use in high electron mobility transistors, as well as optoelectronic devices.
[1] N. Nepal et al., Appl. Phys. Lett. 103 082110 (2013)
[2] N. Nepal et al., Cryst. Growth Des. 13 1485 (2013)
[3] N. Nepal et al., Appl. Phys. Express 6 061003 (2013)