Recent progress of growth techniques of bulk GaN crystals is remarkable for realizing GaN-based power switching devices with a high breakdown voltage. Point defects play important role to characterize the high quality GaN, because structural defects like threading dislocations (TDs) and stacking faults are nearly disappeared. We have been investigating the relation between the near-band-edge (NBE) photoluminescence (PL) lifetime observed at room temperature and the concentration of intrinsic nonradiative recombination centers (NRCs) in n-GaN, of which origins are point defect complexes containing Ga vacancy, by combining positron annihilation spectroscopy (PAS) and time-resolved PL methods [S. F. Chichibu, et al., APL86, 021914 (2005)]. However, PAS becomes less sensitive below the concentration of Ga vacancy ([VGa]) of 10^16 cm^-3. Thus, the development of an alternative way to detect such dilute point defects (<10^16 cm^-3) in high quality GaN crystals is essential.
In this presentation, we will show the quantification of absolute quantum efficiency of radiation (AQE) by employing the omnidirectional PL (ODPL) technique to determine internal quantum efficiency (IQE) of the emission in GaN crystals with different excitation conditions. A high AQE of 8.22% corresponding to IQE of 70.9% was measured at room temperature for the NBE emission of a freestanding-GaN crystal grown by hydride vapor phase epitaxy on a GaN seed crystal manufactured with the acidic ammonothermal method, when cw photo pumping density was 66 W/cm^2.
Kazunobu Kojima, Hirotaka Ikeda, Kenji Fujito, and Shigefusa F. Chichibu, "Determination of absolute quantum efficiency of radiation in nitride semiconductors using an integrating sphere (Conference Presentation)," Proc. SPIE 10532, Gallium Nitride Materials and Devices XIII, 105321R (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2285374.5751536425001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon