Spectroscopic Ellipsometry of Compound Semiconductors: AlxGa1-xN / GaN Hetero-Structures

Determination of the thickness and the dispersion of the AlGaN and the GaN layer in the samples of the GaN and AlGaN films deposited on sapphire substrates.

Group III-Nitrides and their alloys are the most promising materials for short-wavelength optoelectronic devices such as LEDs, injection lasers, photodetectors, full colour displays and electronic devices like HFETs, HEMTs, etc.

For their design and optimization a detailed knowledge of both the layer thickness and the optical properties are essential. Spectroscopic Ellipsometry is a non-destructive optical characterization method that allows determination of these required material parameters.

Liquid Crystal Modulation Spectroscopic Ellipsometry is an excellent technique for the highly accurate characterization of the compound semiconductor heterostructure AlGaN / GaN. Using the MM-16 spectroscopic ellipsometer it is a straightforward procedure to determine the film thickness and optical dispersions of the complete structure even where the film is several microns thick.

The detailed knowledge of the optical parameters of AlGaN alloys is crucial for example for the design of opto-electronic devices. Furthermore, from the optical parameters a calibration curve could be constructed to provide a rapid and efficient determination of the Al content in the AlGaN layers. Thus Spectroscopic Ellipsometry also proves a non-destructive technique for AlGaN alloy composition determination. This method can be equally applied to other compound semiconductors such as SiGe, II-VI semiconductors or classical III-V semiconductors.

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