Infrared spectroscopic ellipsometry - A new tool for characterization of semiconductor heterostructures

Spectroscopic ellipsometry (SE) for infrared wavelengths is presented as a novel technique for contactless and nondestructive measurement of free-carrier and crystal-structure properties of complex semiconductor heterostructures for device applications. Infrared (IR)-active lattice vibrations and LO phonon-plasmon coupled modes dominate the infrared dielectric response of semiconductor materials. Analysis of ellipsometry data from 2 to 33μm can precisely determine thin-film dielectric functions (DF) without numerical Kramers-Kronig analysis and thus provides information on phonon mode frequencies and broadening parameters, static dielectric constants, and free-carrier parameters, even for films with thicknesses only a fraction of the probing wavelengths. Alloy composition, film strain, and crystal quality of sample constituents in thin-film heterostructures can be derived. An infrared dielectric function database, which was established by analysis of simple heterostructures, is used for the investigation of complex device structures. As an example, we demonstrate the characterization of a laser diode (LD) structure based on group-III-nitride materials, where information such as concentration and mobility of free carriers in the n- and p-type regions, thickness, alloy composition, and quality of device constituents are accessible.