Control of the free carrier concentrations in a Si-doped freestanding GaN grown by hydride vapor phase epitaxy

Freestanding GaN was grown on sapphire substrate in a horizontal HVPE system, followed by laser lift-off process. The thickness of the freestanding GaN samples was about 350 μm. Si was used as an n-type dopant and the carrier concentrations were non-destructively measured by micro-Raman spectroscopy. The carrier concentrations of GaN samples were changed from 0.62 to 3.7×1018/cm3 by varying the Si/Ga ratios from 0.01 to 0.04. Crystalline quality of the freestanding GaN was characterized by X-ray diffraction (XRD). The full-width at half-maximum (FWHM) values of the rocking curves of the (102) plane was changed from 96.9 to 317.5 arcsec depending on Si/Ga ratios. This work provides Si/Ga ratios to obtain various carrier concentrations of the freestanding GaN by HVPE, and proposes micro-Raman spectroscopy as a sensitive technique for carrier concentration measurement.