Dependence of thickness and temperature on the thermal stability of Ag films deposited on GaN layers for vertical-geometry GaN-based light-emitting diodes

We investigate the agglomeration behavior of Ag films on GaN as functions of thickness and temperature. The SEM results show that the thinner films become agglomerated at temperatures below 500 C, whereas the thicker films (≥700 nm) remain stable with hillocks at 500 C, (although the density of small holes depends on their thickness). The holes that are formed adjacent to the hillocks lead to the initiation of agglomeration. The X-ray texture analyses exhibit that although the majority of grains are 〈1 1 1〉-oriented, a fraction of them are 〈1 0 0〉-textured when deposited on GaN. For the samples thicker than 700 nm, amount of the 〈1 0 0〉-textured grains increases with increasing temperature, but this is not the case for the samples thinner than 500 nm. The SEM and X-ray pole figure results exhibit that a decrease in the I{2 0 0}/I{1 1 1} pole figure intensity ratios is related to the growth of holes, leading to agglomeration. Based on the SEM and X-ray texture results, the thickness dependence of the texturing and agglomeration behavior of Ag films are described and discussed.