Growth of InGaN nanopyramid arrays on Si for potential photovoltaic applications

InGaN/Si multijunction solar cells form a cost-effective approach for full-spectrum photovoltaics. However, heteroepitaxial InGaN films with high In content are highly defective. To overcome this, nanostructured InGaN growth is explored in this work. Ordered arrays of InxGa1−xN nanopyramids were grown by metalorganic chemical vapor deposition on AlN(0001)/Si(111) substrates in a selective area heteroepitaxy approach. The effect of growth temperature and pressure on the morphology, structure and photoluminescence of the nanopyramids, and their In content x were studied. Reduction in temperature increases x but temperatures <750 °C are correlated with lower structural quality, polycrystalline deposits and In droplet formation. To maintain the quality, a moderately high temperature (~775 °C) may be used. Together with lower pressure, x can be improved. This also enhances the growth rate and improves nanopyramid size uniformity. Nanopyramid arrays generally exhibit greater lattice tilt than their control films due to dislocation bending. While lattice twist is increased with higher x, it is offset by epitaxial lateral overgrowth. Compared to control films, nanopyramid samples consistently yielded higher x, lower average reflectance (<5.5%) and a multi-fold increase in photoluminescence intensity with tunable emission from 3.05 eV to 1.93 eV.