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Normal Incidence Picometer Ellipsometer: Applications

RAS/RDS spectra of different GaAS(001) reconstructions (a) and monolayer oscillations during layer-by-layer growth (b)

Example of RAS spectra and growth oscillations

RAS/RDS has been used to study a range of semiconductors and metals. Among the first applications has been the study of GaAs(001) surfaces during the preparation process in different crystal growth environments. Spectra of these surfaces show a characteristic lineshape depending on the surface reconstruction. As an optical technique, RAS/RDS can be used both in vacuum and gas phase environments, which for the first time gave evidence of the existence of surface reconstructions while growing GaAs(001) in the gas phase with Metal-Organic Vapor Phase Epitaxy (MOVPE). Another important result has been the observation of monolayer oscillations in the RAS/RDS signal during layer-by-layer growth. This effect demonstrates the sub-monolayer resolution of the technique, and has subsequently been used to monitor the growth of multilayer structures. Most standard MOVPE systems can be modified to accomodate RAS/RDS systems such as the Normal Incidence Picometer Ellipsometer, providing for the first time an online in-situ monitor for gas phase growth environments. In addition to monitoring the crystal growth process, the technique can also be applied to study adsorption and desorption processes and other surface effects. Currently the RAS/RDS technique must still be seen as a research tool with a steadily growing number of applications. Monolayer oscillations have been observed for a range of materials including Si(001) and Si compounds. Spectral studies have been conducted on a range of III-V compounds, II-VI and group IV semiconductors, and metals such as Ag, Pt, and Cu.

References

D.E. Aspnes and A.A. Studna, Phys. Rev. Lett. 54, 1956 (1985)

D.E. Aspnes, Mat. Sci. Eng B 30, 109 (1995)

W. Richter and J.T. Zettler, Appl. Surf. Science 101, 465 (1996)