Improved growth rates and purity of basic ammonothermal GaN

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…[52] Furthermore, basic systems exhibit retrograde solubility (increase in temperature leads to a reduction in solubility, Figure 1 b)), while acidic systems typically exhibit normal solubility, though at higher temperatures (>600 °C) they may also exhibit retrograde solubility. Higher solubilities appear to translate into higher growth rates as well, with reported growth rates for basic chemistries laying between 60 and 340 μm per day [22,32] and for acidic between 250 and 960 μm per day. [26,33] Low dissolved Ga concentrations combined with high concentrations of ammonia (NH 3 ) may have an impact on the subsequent incorporation mechanisms of Ga and N into the crystal and the possible formation of defects.…”

“…[20][21][22][23] It is analogous to the hydrothermal method used widely to grow quartz and oxide crystals, but instead of water, ammonia is used as a solvent. One of the primary reasons why the ammonothermal process is of commercial interest is the ability to grow numerous crystals in parallel while requiring minimal labor for supervision once the monthlong growth campaigns have been initiated, thereby significantly reducing cost.…”

“…[24][25][26][27] The current state of the art crystals have a reproducible low TD densities of around 10 4 cm −2 [26][27][28][29] and wafers sliced from ammonothermally grown boules are sufficiently flat with radius of curvature in the order of several hundred meters. [20,30,31] Typical growth rates in the c-direction are in the range of a few hundred micrometers per day [22,26,32,33] and large arbitrary oriented substrates have been demonstrated. [26,[34][35][36] Ammonothermal GaN substrates have been used in homoepitaxy [35,37,38] and as substrates for InGaN LDs.…”

“…[26,[34][35][36] Ammonothermal GaN substrates have been used in homoepitaxy [35,37,38] and as substrates for InGaN LDs. [39] Although the crystalline quality of ammonothermal GaN is very high, recent studies have shown that the high concentration of impurities [22,40,41] and native point defects [42][43][44] in the as-grown material have a significant effect on the material properties. The most dominant impurities, oxygen and transition metals, cause absorption in the visible region [23,42] and their non-uniform incorporation in the growing crystal can cause build-up of strain.…”

“…a) Photograph of a 1 mm thick, bulk basic ammonothermal GaN crystal grown in a silver capsule sliced from a 4 mm thick boule. [22] Slight coloration due to V Ga -H x complexes and broadband absorption due to phonon-assisted free carrier absorption. [42] b) Photograph of a 1 inch diameter GaN boule grown using the basic ammonothermal method in an unlined autoclave.…”