Combined infrared reflectance and Raman spectroscopy analysis of Si-doping limit of GaN

Abstract

Heavily Si-doped GaN layers grown by pulsed sputtering deposition (PSD) on Fe-doped GaN/Al2O3 templates are investigated using infrared reflectance and microscopic Raman measurements. The electron densities (ne) of the Si-doped layer are found to be in the range of 3 × 1018–4 × 1020 cm−3. Signs of transition to over doping is detected for the highest-doping sample by exploiting the advantages of infrared reflectance and microscopic Raman scattering measurements, where we observe a gradual decrease in ne and the highest broadening of the Raman peak of the E2(high) phonon mode toward the surface, and also growing of an additional Raman peak toward the surface, which is attributed to the generation of cubic phase crystal. On the other hand, other samples show spatially uniform ne up to 2 × 1020 cm−3 and small strain in the whole region in the Si-doped layers. This result demonstrates the growth feasibility of highly conductive Si-doped GaN layer by the PSD method.