HVPE-GaN grown on MOCVD-GaN/sapphire template and ammonothermal GaN seeds: Comparison of structural, optical, and electrical properties

Crystallization of GaN by the HVPE technique on an MOCVD-GaN/sapphire template with photo-lithographically patterned Ti mask and ammonothermally-grown GaN crystals (Am-GaN) was studied and compared. Structural and optical properties of the obtained free-standing HVPE-GaN revealed that Am-GaN seeds produced material of much higher quality in terms of etch pit density (EPD), X-ray rocking curves, and excitonic emission than the sapphire-based templates. The crystallization run on the Am-GaN seed, annealed before the growth in H2+NH3 atmosphere, resulted in the HVPE-GaN of an average EPD of 5×104 cm−2, (002) rocking curve width of 22″, and photo-luminescence as narrow as 130 µeV. However, small change in quality was observed when the Am-GaN seed was annealed in N2+NH3 atmosphere prior to growth. In turn, the Hall effect measurements showed that the HVPE-GaN grown on MOCVD-GaN/sapphire template possessed lower free carrier concentration and higher mobility than the HVPE-GaN grown on the Am-GaN seeds. These results were associated to the higher growth rate of the examined HVPE-GaN sample.