Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 59: Optical Properties II

HL 59.10: Vortrag

Mittwoch, 9. März 2016, 17:45–18:00, H10

Optical constants of Ge and GeO2 from ellipsometry — T. Nathan Nunley, Nalin Fernando, Jaime Moya, and •Stefan Zollner — New Mexico State University, Las Cruces, NM, USA

We studied the optical constants of GeO2 and Ge using spectroscopic ellipsometry. Ge substrates were prepared for oxidation by ozone cleaning at 150C for 90 minutes, followed by an ultrasonic clean in DI water, and then in isopropanol. The samples were then annealed in ultra high purity oxygen at 550C at a pressure of 25 psi at a flow rate of 1 l/min. The ellipsometric angles and depolarization were measured using a rotating analyzer ellipsometer with a computer controlled Berek waveplate compensator from 0.5-6.6 eV. X-ray reflectance with Cu radiation was performed to obtain thickness, roughness, and electron density independently. Measurements of the optical phonons were performed at CINT Sandia using FTIR ellipsometry. Samples with 0.1-200 nm GeO2 on Ge were studied, and it was found that the oxidation rate at this pressure was more than twice that previously reported in the literature. The optical constants of GeO2, assumed to be independent of thickness, and the Ge substrate are decoupled by varying the oxide thickness allowing for an optical constant optimization of both the film and the substrate. Using this method we have been able to obtain the optical constants for thermal GeO2 and Ge in the mid infrared and from 0.5-6.6 eV. These data sets will be crucial for the design of Ge based optoelectronic devices and for thickness measurements of thin films on Ge substrates.