Promotion of lateral growth of GaN crystals on point seeds by extraction of substrates from melt in the Na-flux method

Abstract

In a previous study, we successfully obtained large-diameter, low-dislocation-density GaN wafer using the Na-flux multi-point seed (MPS) technique. However, the lattice constants of the GaN wafer grown by this technique expanded due to oxygen concentration in pyramidal facets. We here invented a breakthrough technique for the promotion of lateral growth, and succeed in suppressing pyramidal facet growth by residual flux formed after extraction of the MPS-GaN substrate from the Na-Ga melt in a crucible. The surface of the grown wafer was fully composed of the c-plane and showed low oxygen concentration, so expansion of lattice constants could be successfully prevented.

Terahertz time-domain ellipsometry with high precision for the evaluation of GaN crystals with carrier densities up to 1020 cm−3

“…The first GaN sample (LPE-GaN) was grown on a GaN template using liquid phase epitaxy and has ~ 10 17 cm −3 oxygen concentration 60 , 61 . The second sample (PS-GaN) is a point-seed crystal grown via the Na-flux method and has ~ 10 20 cm −3 oxygen concentration 62 , 63 . Both samples are c -oriented.…”

Prospective view of nitride material synthesis

“…61,75 Refinements are reported where the coalescing crystals are removed from the flux and allowed to grow laterally without further c-plane growth before being re-submerged for c-plane thickening. 76 It appears from literature images that the cross-section of crystals generally decreases based on side-facet formation, limiting the overall thickness of growth. One apparent benefit of the multi-point seeding, however, is the reported self-separation of the grown crystal from its perforated sapphire template.…”

“…One apparent benefit of the multi-point seeding, however, is the reported self-separation of the grown crystal from its perforated sapphire template. 76 In the third area of progress, the researchers in the field have worked extensively on growth process innovations to improve yield, growth speed, and crystal quality. One key technology is the introduction by various mechanisms of improved circulation in the flux.…”

“…In response, researchers from Osaka University developed both a single‐point “necking” technique for decreased dislocation growth, and a related multi‐point seeding technique for producing large wafers with as much as 1000× fewer dislocations than the parent wafer, and many areas reported to be nearly dislocation‐free 61,75 . Refinements are reported where the coalescing crystals are removed from the flux and allowed to grow laterally without further c ‐plane growth before being re‐submerged for c ‐plane thickening 76 . It appears from literature images that the cross‐section of crystals generally decreases based on side‐facet formation, limiting the overall thickness of growth.…”

State-of-the-Art β-Ga2O3 Field-Effect Transistors for Power Electronics

“…In comparison to the well-established SiC and GaN technologies, β-Ga 2 O 3 with a larger energy bandgap (4.9 eV) exhibits higher breakdown electric field (8 MV cm –1 ) and better Baliga’s figure of merit (BFOM) (Table ), suggesting much less power loss incurred in the power devices based on β-Ga 2 O 3 . − The first single-crystal field-effect transistors (FETs) based on β-Ga 2 O 3 homoepitaxial layers were demonstrated in 2012 . Furthermore, since the β-Ga 2 O 3 crystals can be synthesized by various melt growth methods at atmospheric pressure, such as the floating zone (FZ), Czochralski (CZ), and edge-defined film-fed growth (EFG) methods, the cost for producing large-area, uniform, single-crystal substrates can be greatly reduced. − In contrast, the bulk crystals of SiC and GaN can only be manufactured by the less efficient vapor growth methods, such as the sublimation method for SiC crystals and the sodium flux and ammonothermal methods for GaN crystals. − So far, β-Ga 2 O 3 wafers with diameters up to 4 in. have already been demonstrated or commercialized by companies, such as Tamura, Koha, and Novel Crystal Technology .…”