Growth of bulk GaN single crystals by flux method

Abstract

The progresses on the growth of bulk GaN crystals by the flux method in our research group are reported in this review. The research work is mainly focused on the ternary system Li-Ga-N. The phase relations are constructed by the calculation of phase diagram (CALPHAD) technique based on the optimized thermodynamic data of the corresponding binary systems Li-N, Li-Ga and Ga-N. There exists a two-phase region of liquidCGaN at above 750 8C. The well-crystallized, transparent GaN plate-like crystals up to a size of 4 mm can be grown from the Li-Ga-N system under pressures of 1-2 N 2 atmospheres. The yield and quality of the GaN crystals depend on the composition of the starting materials, the growth temperature, the cooling rate, and the position of Li 3 N in the crucible. Efforts are still needed to further enlarge the size of crystals. q

Growth of GaN Single Crystals Using Ca−Li3N Composite Flux

“…However, growing large crystals in a production scale by this method is still a great challenge since the growth conditions (temperatures over 1500 °C and N 2 pressures over 15 kbar) are stringent. A flux method under less stringent conditions reported by Yamane et al was applied to grow GaN single crystals with a size of several millimeters at 600−800 °C and under 50−100 atm of N 2 from the Na−Ga melts. − A more moderate method was employed to synthesize platelet GaN single crystals up to 4 mm at about 800 °C and 1 atm N 2 . − Alkali metal Li is thought to play an important role in the growth of bulk GaN single crystals under such moderate conditions. The method, however, suffers from homogeneous nucleations occurring in random orientations during growth processes, hampering the further increase of the crystal sizes.…”

“…The size distribution of crystals is considered to be closely related to the nucleation process in the crystal growth. The uniform size distribution of the GaN crystal means that the nucleation occurs at a narrower temperature range compared to that in the case with the Li 3 N flux …”

The morphology evolution of selective area wet etched commercial patterned sapphire substrates

“…Patterned sapphire substrate (PSS) is a very critical technology for high-bright GaN-based LEDs [4,5]. PSS not only can improve the internal quantum efficiency (IQE) by reducing dislocations in GaN epi layer but also can enhance the light extraction efficiency (LEE) by introducing light scatter structure [6,7]. To further increase the efficiency of LED on PSS, high-efficiency PSS is continued to be developed toward smaller size and more complicated pattern.…”

Plasma-assisted liquid phase epitaxy of gallium nitride using molten gallium.

“…112 X. L. Chen and collaborators were the first group to propose and use an alkali or semi-alkali metal nitride in conjunction to molten Ga to grow GaN. [113][114][115][116] Their process consisted of placing Li3N and Ga into a tungsten crucible and heating it to ~800°C in a growth furnace, which was pressurized up to 2 atm with N2 gas at room temperature. The crucible was kept at those conditions for 120-180 h and then was cooled down at a rate of 2-3°C/d.…”

“…First, crystals that have been grown through homogeneous nucleation compete with the substrate (seed) used in this process as centers for epitaxial growth. 116,[135][136] Second, crystals can precipitate and deposit onto the substrate surface inducing defects in the LPE grown layers. 137 Lastly, homogeneous nucleation near the surface of the melt promotes the formation of a polycrystalline crust on top of the molten metal.…”