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We propose a new AlN crystal growth method using Fe-based fluxes. AlN single crystals with a thickness of 67–212 µm were epitaxially grown on an AlN bulk substrate by a solution growth method using type 430 ferritic stainless steel flux. The full width at half maximum values of the x-ray rocking curves of (0002) and (10–12) of the synthesized AlN were 137 and 83 arcsec, respectively. The impurity concentrations of carbon were significantly decreased from 3 × 1019 atoms/cm3 in seed crystal to 6 × 1017 atoms/cm3 in synthesized crystal. The features of the method developed in this study are described as follows: (1) steel-based alloys are used as a flux, which are readily available and low-cost; (2) the growth temperature is 1700 °C, which is much lower than that of the sublimation method; (3) no high-pressure vessel is required because growth can be performed under 1 atmospheric pressure conditions; and (4) waste gas detoxification equipment is not required because only N2 gas is used and no toxic or flammable gases are used. Because of the above features (1) through (4), this is an effective crystal growth process from the perspective of ensuring the economics and safety of the facility. [ABSTRACT FROM AUTHOR]

Aluminum nitride is a promising substrate material for AlGaN‐based UV‐LED. In order to develop a robust growth processing route for AlN single crystals, fundamental studies of solution growth experiments using Ni‐Al alloy melts as a new solution system were performed. Al can be stably kept in solution the Ni‐Al liquid even at high temperature; in addition, the driving force of the AlN formation reaction from solution can be controlled by solution composition and temperature. To investigate AlN crystal growth behavior we developed an in situ observation system using an electromagnetic levitation technique. AlN formation behavior, including nucleation and growth, was quantitatively analyzed by an image processing pipeline. The nucleation rate of AlN decreased with increasing growth temperature and decreasing aluminum composition. In addition, hexagonal c‐axis oriented AlN crystal successfully grew on the levitated Ni‐40 mol%Al droplet reacted at low driving force (1960 K), on the other hand, AlN crystal with dendritic morphology appeared on the sample with higher driving force (Ni‐50 mol%Al, 1960 K). Thus, the nucleation rate and crystal morphology were dominated by the driving force of the AlN formation reaction. [ABSTRACT FROM AUTHOR]

Growth of non‐polar AlN layers is important to realize high‐efficiency deep‐ultraviolet light‐emitting diodes. In this study, a‐plane AlN layers are fabricated by a combination of thermal nitridation and Ga–Al liquid‐phase epitaxy (LPE). Thermal nitridation at 1603 and 1623 K provides a‐plane AlN thin films with smooth surfaces on r‐plane sapphire substrates. However, these AlN films contain a double domain structure. Nitridation of r‐plane sapphire with an off‐cut angle can effectively eliminate the double domain structure. Moreover, a‐plane AlN films are grown homoepitaxially on the nitrided r‐plane sapphire substrates by Ga–Al LPE. Thus, a single‐domain non‐polar AlN film is successfully grown on nitrided r‐plane sapphire with an off‐cut angle. [ABSTRACT FROM AUTHOR]

The crystal growth of AlN from aluminum oxides was studied using a thermal nitridation method. Four types of aluminum oxides, sintered Al 2 O 3 , ZrO 2 -containing sintered Al 2 O 3 , and a- and c-plane sapphires, were used as a source material. As observed, millimeter-sized AlN crystal grains were successfully grown from the ZrO 2 -containing sintered Al 2 O 3 only at temperatures ranging from 2223 to 2323 K. The growth mechanism, including the role of ZrO 2 additive, was discussed from a thermodynamic viewpoint. The following growth model was proposed: predominant nitridation of ZrO 2 in Al 2 O 3 suppresses Al 2 O 3 nitridation, and the ZrO 2 –Al 2 O 3 liquid phase forms, which promotes the formation of Al 2 O(g) and Al(g) from Al 2 O 3 . These Al-based gases react with CN(g) and/or N 2 (g) to form AlN crystals on the Al 2 O 3 –ZrO 2 plate. [ABSTRACT FROM AUTHOR]

Previously, we developed Ga-Al liquid-phase epitaxy (LPE) to grow AlN layers on a surface nitrided sapphire substrate using Ga-Al solutions. We found that polarity inversion occurs at the interface between the nitrided sapphire layer and the LPE layer. As the partial pressure of oxygen influences LPE growth, our current study investigated this growth by controlling oxygen in supplying nitrogen gas. Combined with the previous study, we discuss these results in light of the polarity inversion model and growth mechanism for the Ga-Al LPE technique. Oxygen atoms are believed to dissolve in the solution and get trapped on the surface of nitrided sapphire. The trapped oxygen atoms form a symmetrical octahedral structure, which resets the polarity of the nitrided sapphire. Consequently, chemically stable aluminum-polar AlN can be grown in the solution. [ABSTRACT FROM AUTHOR]

The effects of ZrO2 additions to Al2 O3 were investigated to improve the evaporation rate of Al2 O3 for bulk AlN crystal growth. The evaporation rate of Al2 O3 increased concomitantly with increasing ZrO2 concentration under a nitrogen gas stream at 2223 K. The ZrO2 was predominantly nitrided. The nitridation of ZrO2 kept the local oxygen partial pressure high at the pellet surface, which suppressed the nitridation of Al2O3. The nitridation of ZrO2 caused the outward diffusion of ZrO2 (Zr4+ and O2−) in the pellet, which was accelerated further by the presence of Al2O3-ZrO2 liquid phase in grain boundaries, leading to the prompt formation of ZrN porous layer on the pellet surface. The suppressed nitridation of Al2O3 and the formation of porous ZrN layer were the reasons for the enhanced evaporation of Al2O3, leading to enhanced bulk AlN growth. [ABSTRACT FROM AUTHOR]

Bulk AlN single crystal has a great demand as a substrate material for AlGaN-based optical and electronic devices such as deep ultraviolet light-emitting diodes and high-power transistors. We have previously proposed a novel solution-growth method using Ni–Al solution with an in-situ observation system for solution growth of AlN crystal using electromagnetic levitation. In this paper, to investigate AlN formation behavior on 40 mol%Al–Ni droplets, two precisely synchronized high-speed cameras from the horizontal and vertical directions were installed. AlN formation behavior was evaluated quantitatively using computer vision image processing techniques. Based on the results, we demonstrated the growth of thick AlN film at 2030 K for 1 h. A 3.8-μm-thick c-axis oriented AlN film successfully formed on the droplet, and the film was also oriented in-plane. The + c-direction AlN film grew towards the droplet center from the surface by reacting dissolved nitrogen and Al atoms. • The authors have developed an original solution growth method using Ni–Al melt. • AlN growth on Ni–Al droplet was investigated precisely by our original system. • AlN formation behavior was evaluated using computer vision image processing. • A 3.8-μm-thick c-axis and in-plane oriented AlN film formed on the Ni–Al droplet. [ABSTRACT FROM AUTHOR]