Ternary Indium Gallium Nitride (InGaN) alloys posses a direct bandgap that can be tuned across the largest part of the solar spectrum (0.7 to 3.4 eV). Therefore, they are very promising candidates for the development of efficient solar cells. Towards this goal, a number of issues, related to epitaxial growth and phase separation phenomena, need to be addressed.
For photovoltaic applications, it is necessary to achieve thin films with high InN content (higher than 0.2 mol%), while controlling alloy homogeneity, which is challenging due to strong immiscibility of the binary constituents. Plasma assisted molecular beam epitaxy, in principle, can address this bottleneck, due to its metastable epitaxial growth character. However, the vastly different growth modes of GaN and InN, along with indium segregation and InGaN decomposition phenomena, complicate the epitaxial growth.
In this presentation, the investigations of growth kinetics of RF-MBE epitaxy of InGaN(0001) will be presented. For low growth temperatures, InGaN decomposition seems to be the dominant mechanism dictating the effective growth conditions. There are evidence that InGaN decomposition during growth is strongly influenced by surface phenomena and relates not only to the film composition and temperature but also to the adatoms arrival rate on the surface. For higher temperatures, when In desorption becomes more prominent, the conditions seem to be governed by the interplay of the two mechanisms. The “growth window” leading to high quality epitaxial films of sufficient thickness, throughout the whole composition range, is identified. Furthermore, the influence of growth conditions, especially the growth temperature, on the occurrence of phase separation, as well as, on the different strain relaxation mechanisms involved (sequestration, introduction of threading dislocations and stacking faults and V-pits formation) will be discussed, along with the investigations of films’ optoelectronic properties.