Abstract
Using a mass-loss method, we investigated the solubility change of gallium nitride (GaN) in supercritical ammonia with mixed mineralizers [ammonium chloride (NH4Cl) + ammonium bromide (NH4Br) and NH4Cl + ammonium iodide (NH4I)]. The solubilities were measured over the temperature range 450–550 °C, at 100 MPa. The solubility increased with NH4Cl mole fraction at 450 °C and 100 MPa. The temperature dependence of the solubility curve was then measured at an equal mole ratio of the two mineralizers. The slope of the solubility–temperature relationship in the mixed mineralizer was between those of the individual mineralizers. These results show that the temperature dependence of the solubility of GaN can be controlled by the mineralizer mixture ratio. The results of the van’t Hoff plot suggest that the solubility species were unchanged over the investigated temperature range. Our approach might pave the way to realizing large, high-quality GaN crystals for future gallium-nitride electronic devices, which are increasingly on demand in the information-based age.
Highlights
In an increasingly information-based society, high-speed wireless communications systems with massive information-transmission capability are expected as a ubiquitous network technology in the near future
The measured solubilities of gallium nitride (GaN) in supercritical ammonia with mixed mineralizer compositions of NH4Cl + NH4Br and N H4Cl + NH4I are given in Tables 1 and 2
In the NH4Cl + NH4Br mixture, the GaN solubility curve became gradually convex with increasing molar fraction of NH4Cl, but in the NH4Cl + NH4I mineralizer, it was an almost-linear function of NH4Cl molar fraction
Summary
In an increasingly information-based society, high-speed wireless communications systems with massive information-transmission capability are expected as a ubiquitous network technology in the near future To realize such systems, the power and operating frequency of electronic devices need to be increased. Gallium-nitride devices offer a promising solution, as their power and frequency is expected to exceed those of Si-based devices These devices require a large-diameter, highquality GaN bulk single-crystal substrate, which does not yet exist. Heteroepitaxial growth can be carried out on sapphire substrate by the hydride vapor phase epitaxy (HVPE) method, the lattice mismatch increases the dislocation density of the growth For this reason, there has been a race to develop bulk GaN singlecrystal substrates using various methods. Controlling the temperature dependence of GaN solubility by altering the mineralizer-mixing ratio would be very useful for ammonothermal crystal growth, Tomida et al Chemistry Central Journal (2018) 12:127 because mineralizer addition is an adjustable parameter
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