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1 2004

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Photoreflectance and photoluminescence of thick GaN layers grown by HVPE

Kudrawiec R., Korbutowicz R., Paszkiewicz R., Syperek M., Misiewicz J.

Opto-Electronics Review

2004

Vol. 12, No. 4

435-439

Very thick (up to 100 µm) GaN layers grown by HVPE are investigated by photoreflectance (PR) and photoluminescence (PL) spectroscopies. The layers were deposited on a GaN buffer layer which was grown on a c-plane sapphire substrate by MOVPE. Both, N- and Ga-polar layers were selected to these investigations. We have observed a strong dependence of the optical properties on the polarity of GaN surface. We have obtained that the bandgap-related emission for Ga-polar layers is stronger and narrower than the emission for N-polar layers. Also, significant differences have been found in PR spectra of the two type layers. In the case of Ga-polar layer a broad PR resonance with Franz-Keldysh oscillation (FKO) related to the surface electric field (215 kV/cm) has been observed, while in the case of N-polar layer narrow resonances have been found as being predominant. No-FKO for N-polar layer indicates that the surface electric field for this layer is weak. It means that the surface barrier for N-polar GaN is much smaller than for Ga-polar GaN layer.