Influence of reaction conditions on the growth of GaN rods in an ammono-CVD reactor

GaN was deposited onto a sapphire substrate covered by gold film to favor formation of rods in a chemical vapor deposition reactor. Sublimation of NH ₄Cl was used to transfer gallium to the vapor phase and it was then reacted with NH₃. A factorial design experiment was used to study three parameters: substrate temperature, ammonia flow and temperature applied to NH₄Cl. Results showed that the three parameters interact with each other with respect to the lateral growth of GaN, e.g. the rise in substrate temperature can either increase or reduce the lateral growth depending on the NH₄Cl treatment temperature. Similarly, the catalytic effect of gold on GaN rods depends on the three studied parameters. These interactions cannot be observed in univariate experiments. Optimal conditions to produce GaN rods were a substrate temperature of 800 °C, ammonia flow of 180 sccm and 300 °C applied to NH₄Cl. The V/III ratio was a dominant factor in lateral growth, and this is controlled simultaneously with the three parameters studied.