Preparation and Optical Performance of Freestanding GaN Thick Films

Abstract:

High-quality freestanding GaN thick films were deposited by hydride vapor phase epitaxy (HVPE) on sapphire wafer with a thin Ti film on the top. The FWHM of (0002) peaks in the X-ray rocking curve profile is 260 arcsec. The FWHM of band edge emission peaks at 5 K and room temperature are 3 meV and 20 meV, respectively. The yellow spectral region is not observed at room temperature. The surface morphology of GaN films was characterized by scanning electron microscope; results show that hexagonal pits from dislocation extension exist on the surface of freestanding GaN thick films after corrosion and their dislocation density is estimated as 2.1×l07 cm-2. All these results prove that the Ti metal interlayer improves the crystalline quality of GaN epitaxial layer. The results of Raman and PL show that the surface stress of the GaN films is released completely. Finally, the temperature-dependent PL was investigated; the result also proves that the stress-free freestanding GaN thick films have high crystalline quality and optical quality

Key words:GaN; HVPE; freestanding thick films; stress release; photoluminescence