Quanxi Bao

Acidic ammonothermal growth of GaN crystals using GaN powder as a nutrient

Ammonothermal crystal growth of gallium nitride (GaN) was realized for the first time using GaN powder as a nutrient with growth rates of about 61 μm per day on both Ga and N faces. The GaN powder was synthesized by ammonolysis of Ga metal in the presence of NH4I. The crystal quality of the as-grown GaN wafers was characterized by scanning electron microscope (SEM), X-ray rocking curve (XRC) and photoluminescence (PL) measurements. We examined the effect of different nutrients, including polycrystalline GaN, Ga metal, and GaN powder, on the acidic ammonothermal crystal growth of GaN using an NH4I-based mineralizer. Our results suggest that growth rate and crystal quality of GaN depend largely on the type of nutrient. Polycrystalline GaN as a nutrient can afford high growth rates of up to 150 and 237 μm per day on Ga and N faces, respectively. Growth rates up of to 33 μm per day were achieved using Ga metal as a nutrient. However, SEM, XRC, and PL measurements of GaN crystals grown using different nutrients indicate that Ga metal and GaN powder nutrients can provide better crystal quality of GaN in terms of surface morphology and crystal uniformity than polycrystalline GaN.

Powder synthesis and ammonothermal crystal growth of GaN from metallic Ga in the presence of NH4I

An efficient and mild method to synthesize high-purity hexagonal GaN powder using NH4I as a catalyst was developed. The method makes it possible to use Ga metal for ammonothermal crystal growth of GaN at a rate of 20 μm per day, which is comparable to its growth rate using polycrystalline GaN grown by hydride vapor phase epitaxy as a nutrient.

Ammonothermal crystal growth of gallium nitride using ZnCl2 as mineralizer

Ammonothermal crystal growth of GaN on a HVPE grown GaN seed is realized using ZnCl2 as a novel acidic mineralizer. Compared with other NH4X acidic mineralizers (X: Cl, Br and I), ZnCl2 provides significantly increased crystal growth speed and improved crystal quality under milder operating conditions.

High quality bulk GaN crystal grown by acidic ammonothermal method

Acidic ammonothermal method is one of the most promising techniques which enable the mass production of large diameter bulk GaN crystal. State-of-the-art high-power light-emitting diodes and laser diodes are usually fabricated on GaN substrates grown by hydride vapor phase epitaxy. However, to realize vertically conducting high-power GaN switching devices, bowing-free large-diameter GaN substrates are essential, because the size of such devices is much larger than that of optical devices. Our group has been studying the characteristics of supercritical NH3 using ammonium halides as mineralizers, and succeeded in growing GaN. The crystal quality and the growth rate strongly depend on mineralizer species. We have also studied the dependence on temperature and pressure, and found it possible to achieve the growth rate faster than 1000μm/day in the optimum growth condition. Based on these studies and optimization, we have successfully demonstrated high speed bulk GaN growth at the pressure condition at 100MPa.