Characterization of High-Quality Free-Standing GaN Grown by HVPE

Single-crystalline 330µm thick GaN has been grown on 2'' Al2O3 (0 0 0 1) by hydride vapour phase epitaxy (HVPE). Upon laser-induced lift-off the GaN was delaminated from the sapphire substrate, and bulk-like free-standing GaN was achieved. Various characterization methods were utilized to assess the structural and optical quality of the freestanding material. The X-ray rocking curves of the (1 0–1 4) and (0 0 0 2) diffraction peaks revealed full width at half maximum (FWHM) values of 96 and 129arcsec, respectively. These data compare well with the smallest corresponding values published so far for bulk-like HVPE-GaN. The dislocation density determined by plan-view transmission electron microscopy studies is 1–2 × 107cm–2. The low-temperature near-band-gap photoluminescence spectrum shows the main donor bound exciton (DBE) peak at 3.4718eV with a FWHM of 1.4meV, verifying the high crystalline quality of the bulk-like GaN. The DBE peak position suggests complete stress relief. The phonon spectra measured by infrared spectroscopic ellipsometry confirm as well, that the free-standing material is of high crystalline quality and virtually stress-free.