| AVS 57th International Symposium & Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM+SS-ThM |
| Session: | Nitride Surfaces and Interfaces |
| Presenter: | A.R. Smith, Ohio University Nanoscale and Quantum Phenomena Institute |
| Authors: | A.R. Smith, Ohio University Nanoscale and Quantum Phenomena Institute T. Chen, Ohio University Nanoscale and Quantum Phenomena Institute K. Wang, Ohio University Nanoscale and Quantum Phenomena Institute Y. Liu, Ohio University Nanoscale and Quantum Phenomena Institute |
| Correspondent: | Click to Email |
The wurtzite GaN(0001) surface has previously been determined to be in a pseudo-1x1 structure which includes approximately 2 monolayers (ML's) of Ga sitting atop the last GaN bilayer [1]. This metallic structure, commonly observed, was initially determined using a combination of reflection high energy electron diffraction (RHEED), Auger electron spectroscopy, and scanning tunneling microscopy (STM). In addition, there has been theoretical work performed for this surface. [2,3] In RHEED, the main observation is the appearance of satellite streaks located at 1/6th (or 1/12th) of the primary streak spacing outside of the primary streaks. It was initially modeled as a bi-axially contracted Ga bi-layer, contracted by approximately 16% relative to the GaN bulk. Theoretical calculations found only the top Ga ML to be contracted bi-axially. More recent theory work by Rinehimer et al. suggest that instead it is uniaxially contracted but having a similar structure. [3]
We investigate the pseudo-1x1 structure experimentally using a new growth and analysis system consisting of a molecular beam epitaxy (MBE) chamber for preparation of the surface and a RHEED system to monitor it. The sample growth stage also has the feature of allowing cooling to cryogenic temperatures as well as heating. The pseudo-1x1 structure is prepared by MBE growth on MOCVD-grown GaN substrates. Following this, the sample is cooled down, and the diffraction pattern is monitored. At low temperature, we observe the onset of new diffraction streaks located at approximately 5/12 and 7/12 of the primary streak positions, as well as disappearance of the pseudo-1x1 satellite streaks.
Models for the low-temperature GaN(0001) structure are currently being formulated which may give new insights into the structure of the pseudo-1x1, based on this new low-temperature RHEED data. As one model currently under consideration, a uniaxial, aperiodic superstructure is proposed in which the top Ga layer freezes into a coherent layer but with the resultant extra Ga atoms being displaced vertically. To further probe this model, low-temperature STM experiments are currently being planned, to be conducted in an adjacent in-situ STM system. This work is supported by the National Science Foundation (Grant No. 0730257) and by a grant from Ohio University.
[1] A. R. Smith, R. M. Feenstra, D. W. Greve, M.-S. Shih, M. Skowronski, J. Neugebauer, and J. E. Northrup, J. Vac. Sci. Technol. B 16 (4), 2242 (1998).
[2] J. E. Northrup, J. Neugebauer, R. M. Feenstra, A. R. Smith, Phys. Rev. B 61, 9932 (2000).
[3] J.A. Rinehimer, M. Widom, J.E. Northrup, and R.M. Feenstra, Phys. Stat. Sol. (b) 245(5), 920 (2008).