Time-resolved photoluminescence (TRPL) and positron annihilation measurements, as well as Al 0.23Ga 0.77N/GaN heterostructure growth by metalorganic vapor phase epitaxy were carried out on very low defect density, polar c-plane and nonpolar m-plane freestanding GaN (FS-GaN) substrates grown by hydride vapor phase epitaxy. Room-temperature photoluminescence (PL) lifetime for the near-band-edge (NBE) excitonic emission of the FS-GaN substrates increases with increasing positron diffusion length (L +); i.e., decreasing gross concentration of charged and neutral point defects and complexes. The best undoped c-plane FS-GaN exhibits record-long L + being 116 nm. The fast component of the PL lifetime for its NBE emission increases with temperature rise up to 100 K and levels off at approximately 1.1 ns. The result implies a saturation in thermal activation of nonradiative recombination centers. The surface and interface roughnesses for a Si-doped Al 0.23Ga 0.77N/GaN/Al 0.18Ga 0.82N/GaN heterostructure are improved by the use of FS-GaN substrates, in comparison with the structure fabricated on a standard GaN template. The emission signals related to the recombination of a two-dimensional electron gas and excited holes are recognized for an Al 0.23Ga 0.77N/GaN single heterostructure grown on the c-plane FS-GaN substrate.
ASJC Scopus subject areas
- Physics and Astronomy(all)