Synthesis of AlN from Li₃N and Al: Application to vapor phase epitaxy

We performed synthesis of AlN using Al and Li₃N. In this method, there are two problems that must be solved for obtaining single-phase AlN. One of them is suppression of Li₃AlN₂ formation and the other is precipitation of LiAl from the residual source materials during the cooling process. In the present work, we analyzed phase stability of products and found that AlN was stable at high temperatures and low Li-N/Al molar ratios. However, the products still contained LiAl and Al. Therefore, we examined the effectiveness of vapor phase epitaxy for separating AlN from the extra phase (LiAl and Al formed from residual source materials). From the experimental results, feasibility of vapor phase epitaxy was confirmed. That is, we can deposit only an AlN layer on a sapphire substrate by optimizing the growth conditions, i.e., temperature range above 1150 °C and Li-N/Al molar ratio less than 1.