Optical Characterization of Radio-Frequency Magnetron-Sputtered Gallium-Arsenide Films under Non-Uniform Thickness Conditions
T.Z.A. Zulkifli1, D.L. Rode2a, L.H. Ouyang3, and B. Abraham-Shrauner2b
1 School of Electrical Electronic Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malayasia
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Department of Electrical Engineering,
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Measurements were carried out on radio-frequency magnetron-sputtered amorphous and microcrystalline gallium-arsenide (GaAs films, which were fabricated under various sputtering conditions such as annealing temperature (up to 450oC), substrate temperature (up to 200oC), sputtering pressure (up to 20 mTorr), rf sputtering power (up to 800W), and hydrogen partial pressure (25% H2 in a mixture with 75% Ar). The experimental goals were to obtain GaAs films exhibiting a low optical absorption coefficient (<100 cm-1) and a high index of refraction (n>3.5) for wavelengths greater than 1,000 nm. The key contribution of this work is the introduction of a novel, simple technique to calculate the absorption coefficient under conditions of non-uniform film thickness. The absorption coefficient calculated using the new technique generally decreases as a function of increases in annealing temperature (up to 450oC), substrate temperature (up to 200oC), sputtering pressure (up to 20 mTorr), rf sputtering power (up to 800 W), and hydrogen partial pressure (25% H2 in a mixture with 75% Ar). Index of refraction, on the other hand, generally decreases as a function of the parameters above except for the case of rf sputtering power, where the index of refraction significantly increases. The absorption coefficients obtained in this research are the lowest vlues ever published using conventional spectrophotometry.