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HL: Fachverband Halbleiterphysik

HL 24: Nitrides: Preparation and characterization I

HL 24.4: Vortrag

Mittwoch, 3. April 2019, 10:15–10:30, H31

All-optical determination of free-carrier concentration and composition in cubic GaN and AlGaN — •Elias Baron¹, Michael Deppe², Fabian Tacken², Donat Josef As², Martin Feneberg¹, and Rüdiger Goldhahn¹ — ¹Institut für Physik, Otto-von-Guericke-Universität Magdeburg, Germany — ²Department Physik, Universität Paderborn, Germany

The doping by Ge is shown to be a very efficient way to achieve free electron concentrations n above 10²⁰cm⁻³ in wurtzite and zincblende GaN and AlGaN layers, while maintaining excellent structural properties. Here, thin films of zincblende III-N were deposited by plasma-assisted molecular beam epitaxy on 3C-SiC substrates. Utilizing Kane’s model and the optical effective mass in semiconductors a consistent approach to determine the band structure near the Γ-point of the Brillouin zone is achieved, which is necessary to understand the optical properties. We present a characterization of GaN and AlGaN by spectroscopic ellipsometry from which the complex dielectric function (DF) is obtained. The analysis of the DFs in the mid-infrared yields the transverse-optical phonon frequencies as well as the plasma frequency for doped material. From the latter, the free-carrier concentration can be deduced. On the other hand, studies around the fundamental absorption edge indicate the superposition of n dependent Burstein-Moss effect, band gap renormalization and in case of AlGaN band gap bowing. A self-consistent description of plasma frequency and absorption onset yields both the free-carrier concentration and the composition in case of AlGaN.