Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 31: Poster: Nitrides

HL 31.3: Poster

Montag, 31. März 2014, 17:00–20:00, P2

Terahertz spectroscopy of electron transport in GaN — •Thomas Rene Arend¹, Stefan Gerhard Engelbrecht¹, Menno Johannes Kappers², and Roland Kersting¹ — ¹Photonics and Optoelectronics Group, Ludwig-Maximilians-Universität München, Germany — ²Department of Materials Science and Metallurgy, University of Cambridge, UK

Structural imperfections in epitaxial GaN, such as threading dislocations and surface inhomogeneities limit the electronic conductivity. Terahertz (THz) spectroscopy is applied for characterizing charge transport in n-doped GaN fabricated by MOVPE. We use Schottky devices that allow for switching the electron density. The resulting differential THz signal is proportional to the high frequency conductivity of the electrons. Devices with low threading dislocation density (4e8cm-2) and low doping density (5e16cm-3) show the classical Drude response. Increasing the dislocation density to 4e9cm-2 leads to unexpected deviations from Drude behavior, such as a negative imaginary conductivity at low frequencies. Even more drastic is the impact of a high doping concentration (4e18cm-3), which leads to a negative imaginary conductivity over the entire THz spectrum accessible. The experimental data are well reproduced by the Bruggeman model, where we assume a conducting and an insulating phase. The calculations deliver the ratios of the components as well as scattering times and mobilities. In all samples, the scattering times are about 50fs. But increasing the doping concentration or the density of threading dislocations decreases the volume fraction of the conducting phase from 95% to about 50%.