Gallium antimonide (GaSb) has attracted strong attention as new channel material which can enable a high performance and low power consumption complementary metal–oxide–semiconductor (CMOS) technology, because it has extremely high bulk mobility for holes (850 cm²/Vs at 300K), narrow band gap (0.72 eV at 300K) and an excellent lattice match with various III-V ternary and quaternary compounds [1-3]. The performance of a CMOS transistor is strongly dependent on the surface characteristics, such as chemical state, surface roughness and oxide thickness. Therefore, in order to introduce GaSb as a channel in semiconductor transistors, effective surface preparation with an understanding of its surface chemistry is imperative. In this study, the effects of H₂O and H₂O₂on the GaSb (100) oxidation surface were studied by analyzing the oxide layer thickness, hydrophobicity, and chemical states of the GaSb surface with ellipsometry, contact angle measurement and X-ray photoelectron spectroscopy, respectively. In addition, reaction kinetics and oxidation mechanism of GaSb in various acidic and basic cleaning solutions were investigated.

As shown in Fig. 1, the treatment of Si, Ge, InAs and InSb surfaces in diluted H₂O₂ solution made their surfaces hydrophilic as compared to that in H₂O, which is because the semiconductor surfaces were more oxidized in H₂O₂ [4]. However, GaSb surface immersed in diluted H₂O₂ solution exhibited more hydrophobic property than that treated in H₂O. In addition, it was observed from ellipsometer measurements that oxide thickness on GaSb surface was thicker after dipping in H₂O than in H₂O₂, and its thickness increased with the dipping time in H₂O, while no significant change was found in H₂O₂treatment (Data not shown here), which is in consistency with the contact angle results.

After treatment of the GaSb surface in H₂O, the ratio of Ga₂O₃ increased as shown in Fig. 2(a), which can be ascribed to the rapid oxidation of GaSb in H₂O [5]. When the surface was subsequently dipped in dilute H₂O₂ solution, the component of Ga₂O₃ rapidly decreased. Conversely, a GaSb surface treated in dilute H₂O₂ solution showed a slightly higher Ga₂O₃ ratio as compared to DHF treatment, but far lower than that treated in H₂O at a same process time (Fig. 2(b)). When the H₂O₂-pretreated surface was subsequently dipped in dilute H₂O, it is observed that the Ga₂O₃ was significantly increased. Those XPS results are consistent with our contact angle (Fig. 1) and ellipsometer results. As a result, it is suggested that H₂O₂serves as an inhibitor of oxidation on the GaSb semiconductor surface. XPS spectra of Sb3d show similar trends as Ga3d.

For further study, GaSb surface was treated in the solutions ranging from pH 1~7. While the surface was almost oxide-free in case of pH between 1 and 3, oxide significantly increased from pH over 4, as one can easily see from Ga3d XPS spectra in Fig. 3(a). The behavior of GaSb surface shown in Fig. 3(a) exhibited a close match with the results of contact angle measurements shown in Fig. 3(b). The results shown in Figs. 3(a) and (b) are explained by Pourbaix diagram shown in Fig. 3(c) [6]. When the GaSb surface dipped in the solution of pH over 3, oxidation is the dominant reaction on the GaSb surface rather than etching of oxide, while etching is dominant at the pH below 3. It is suggested that the GaSb surface in an acidic solution will be etched to form aqueous Ga³⁺ or Ga(OH)²⁺ ions, which results in a hydrophobic semiconductor surface. Further mechanisms for the behaviors of GaSb surface in the solution in the presence of H₂O₂and in acidic and basic solutions have been extensively studied, and will be presented at the conference.

 

 References

[1]   J. A. del Alomo, Nature, 479, 317 (2011).

[2]   S. Basu, N. Basu, P. Barman, Mater. Sci. Eng. B, 9, 47 (1991).

[3]   A. Nainani, T. Irisawa, Z. Yuan, B. R. Bennett, J. B. Boo, Y. Nishi, K. C. Saraswat, IEEE Trans. Electron Dev., 58, 3407 (2011).

[4]   G. C. DeSalvo, W. F. Tseng, J. Comas, J. Electrochem. Soc., 139, 831 (1992).

[5]   D. Seo, J. Na, S. Lee, S. Lim, J. Phys. Chem. C, 119, 24774 (2015).

[6]   M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions; National Association of Corrosion Engineers: Houston, Texas, 1974.