Influence of GaN/sapphire contact area on bowing of GaN wafer grown by the Na-flux method with a sapphire dissolution process

Abstract

Although almost all freestanding GaN crystals exhibit concave bowing despite the elimination of a seed substrate, in the Na-flux multipoint-seed technique, a flat GaN substrate is stably obtained. Unlike other hetero-epitaxial growth techniques, this method allows the GaN/sapphire contact area to be minimized, and this in turn can lead to low curvature. However, the detailed mechanism underlying this effect on curvature is unclear. Therefore, in this study we investigated the relationship between the curvature and the GaN/sapphire contact area of freestanding GaN crystals with the use of a sapphire dissolution technique to eliminate thermal stress. As a result, the radii of the lattice curvatures of the grown crystals increased with a decrease in the contact area, and a GaN substrate with a large diameter (>2 in) and low curvature (>40 m) was obtained. These results may be attributed to grain coalescence on a flat seed.

Fabrication of GaN crystals with low threading dislocation density and low resistivity by thin flux growth in the Na-flux point seed technique

“…In the Na-flux PS technique, the reduction of the contact area ratio leads to the reduction of the bowing of the seed crystal during growth, resulting in a flat crystal. 21) TDD was estimated from the etch pit density in a 170 × 170 μm square area of SEM images with a mapping of 51 points, as shown in Fig. 5.…”

Photoluminescence and scintillation properties GaN

“…33) As is well-known, pulse height spectrum is the most important feature of scintillation detectors. Up to now, there have been many researches on optoelectronic properties of GaN [34][35][36][37][38][39][40][41] while the number of studies on scintillation properties is limited. 33,[42][43][44][45][46][47] Among these past works, only one paper reported a pulse height spectrum by scintillation of GaN but under neutron irradiation 47) and the LY was not determined quantitatively, most likely due to low LY.…”