Materials Research Society Symposium Proceedings 468, 225 (1997).
Below is the abstract submitted to the meeting, not the abstract of the published paper:
A major problem in growing GaN layers on standard substrates as, e.g., sapphire or GaAs, is the large lattice-mismatch and the difference in the thermal expansion coefficients between layer and substrate. This causes a large biaxial stress in the layers, which is either compressive for hexagonal GaN on sapphire, or tensile for cubic GaN on GaAs. In order to handle thin-film heterostructures based on GaN, a knowledge of the internal stress is necessary. Experimental information about the main strain parameters in particular for cubic GaN is still lacking. We performed low-temperature (10 K) Raman-scattering experiments on GaN layers grown on GaAs at high hydrostatic pressures up to 6 GPa. We determined the Gruneisen parameters of the cubic TO and LO phonon modes as well as of the hexagonal E2 mode. We also observed the appearance of an additional high-frequency Raman mode (625 cm-1 at 5.3 Gpa) for pressures higher than 3 GPa. We found that the mode Gruneisen parameters for the GaAs substrate are about 30% smaller than those of bulk GaAs. This is a consequence of the low compressibility of GaN compared to GaAs, which results in a pressure-induced biaxial strain of the substrate. From the pressure behavior of the GaAs modes, we obtained information about the biaxial strain in the GaN layers.
This paper is part of Gallium Nitride and Related Materials II
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