Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 22: GaN: Pr
äparation und Charakterisierung I

HL 22.7: Talk

Saturday, March 5, 2005, 12:15–12:30, TU P-N201

The temperature dependence of the thermal expansion of GaN — •Claudia Roder, Sven Einfeldt, Stephan Figge, and Detlef Hommel — Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee, 28359 Bremen

In the case of epitaxial layers grown on foreign substrates the difference in the thermal expansion coefficients between the layer material and the substrate material governs the strain induced in the layer during cool-down from growth to room temperature. Since the strain determines various important parameters of GaN such as the bandgap, the accurate knowledge of the thermal expansion is essential not only from a physical point of view but also for device engineering. The thermal expansion of GaN bulk crystals was investigated in an extended temperature range from 12 to 1025 K. The lattice parameters a and c were measured by high-resolution x-ray diffraction. The temperature dependence of the derived thermal expansion coefficients along the a and c directions could be perfectly described over the entire temperature range within both the Debye model and the Einstein model for the lattice vibrations. Debye and Einstein temperatures were derived along the a and c axes, respectively.