| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS+AS+EM-WeA |
| Session: | Semiconducting Surfaces |
| Presenter: | Shunji Goto, The University of Electro-Communications (UEC-Tokyo), Japan |
| Authors: | S. Goto, The University of Electro-Communications (UEC-Tokyo), Japan A. Ohtake, National Institute for Materials Science (NIMS), Japan J.N. Nakamura, The University of Electro-Communications (UEC-Tokyo), Japan |
| Correspondent: | Click to Email |
GaAs surfaces are stabilized by surface treatments with S or Se because of the reduction of the dangling bond density [1,2]. Recently, it has been reported that when the GaAs(111)B-(2 x 2) As trimer surface is treated with Se, the diffraction pattern changes from (2 x 2) to (1 x 1) [3]. The Se-treated GaAs(111)B-(1 x 1) surface was considered to have a simple structure; all As atoms of the ideal (111)B surface are replaced by Se atoms. However, a scanning tunneling microscope (STM) image shows highly disordered array of bright features with a density of 0.25 per (2 x 2) unit [4,5]. This is incompatible with the simple structure model for (1 x 1). Very recently, another structure model has been proposed for the Se-treated surface, where three As atoms on the topmost surface are replaced by Se atoms per (2 x 2) unit. This As / Se terminated model is electronically stable because the so-called electron counting rule is satisfied and the STM simulations for this model reproduces the most of features of STM experiments. In this study, we discuss the structural stability of the As / Se termination model from the viewpoint of the formation energy. We depict a phase diagram as functions of chemical potentials of Se (μ(Se)) and As (μ(As)) using the first-principles calculations within the density functional theory.
Under the As-rich and Se-poor conditions, the (2 x 2) As-trimer surface is the most stable phase. The As / Se terminated surface appears in the phase diagram under more As (Se) poor (rich) conditions, being consistent with the recent experiment [5]. It is noted that the fully-Se-terminated (1 x 1) surface can exist as a stable phase in the limit of Se-rich condition, whereas this surface does not satisfy the electron counting rule and has a metallic surface state attributed to surplus electrons of Se. At the fully-Se-terminated surface, a lone pair forms at each Se site and resultant excess electrons occupy the anti-bonding orbital of the outermost bilayer. As a result, the surface Se atoms hardly leave any dangling bond. We have also found that the S-treated surface is passivated by a similar mechanism.
[1] J. Fan, H. Oigawa and Y. Nannichi, Jpn. J. Appl. Phys. 27 L2125 (1988).
[2] V. N. Bessolov and M. V. Lebedev, Fiz. Tekh. Poluprovodn 46, 10201 (1998).
[3] D. A. Woolf, Z. Sobiesierski, D. I. Westwood, and R. H. Williams, J. Appl. Phys. 71, 4908 (1992)
[4] A. Ohtake and Y. Sakuma, Cryst. Growth Des. 17, 363 (2017).
[5] A. Ohtake, S. Goto, and J. Nakamura, Sci. Rep., 8, 1220 (2018).