Berlin 2012 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 4: GaN: Preparation and Characterization I (mainly Optics)
HL 4.7: Vortrag
Montag, 26. März 2012, 11:00–11:15, EW 201
Raman spectroscopic characterization of freestanding GaN layers — •Christian Röder1, Frank Lipski2, Cameliu Himcinschi1, Jens Kortus1, and Ferdinand Scholz2 — 1TU Bergakademie Freiberg, Institute of Theoretical Physics, Leipziger Str. 23, D-09596 Freiberg, Germany — 2Ulm University, Institute of Optoelectronics, Albert-Einstein-Allee 45, D-89081 Ulm, Germany
In contrast to established growth techniques of other semiconductor materials, GaN technology is currently based on heteroepitaxy on foreign substrates like sapphire (0001), 6H-SiC (0001) or silicon (111). Due to the lattice mismatch and the difference in the thermal expansion coefficients between GaN and substrates there are serious problems such as a large density of defects and structural imperfections as well as high induced stress.
In this work we investigated several GaN layers separated from the sapphire substrate during cool-down from growth temperature. This allows to avoid thermal stress induced by mismatch of the thermal expansion coefficients. Using confocal Raman spectroscopy we obtained depth spatial information. We have chosen to analyze the position of the non-polar E2(high) phonon mode which is only affected by strains. Assuming a planar stress state the determined wavenumber shifts were converted to stress values. Additionally, photoluminescence (PL) measurements were performed at 87 K being in good agreement with the Raman results.
The authors would like to thank the European Union (EFRE) as well as the Free State of Saxony for financial support within the ADDE project.