Journal article

Thermal stability of GaN investigated by Raman scattering

We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of structural damage to GaN by high-temperature anneals in nitrogen ambient has been demonstrated. Characteristic features in the Raman spectrum identify three thermal stability regimes. Thermal damage between 900 and 1000 degrees C results in the appearance of a broad Raman peak between the E-2 and A(1) (LO) phonon. For anneals at temperatures higher than 1000 degrees C emerging macroscopic disorder gives rise to distinct Raman modes at 630, 656, and 770 cm(-1). Below 900 degrees C no thermal damage has been observed. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for a reaction at the GaN/sapphire interface for anneals higher than 1000 degrees C. (C) 1998 American Institute of Physics.


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