3D heteroepitaxy on patterned Si substrates: a new monolithic integration strategy

We have recently shown that crystal defects and internal stresses commonly hampering Ge heteroepitaxy on Si can be greatly reduced by promoting the nucleation of micro-crystals at the top of Si pillars deeply patterned on the substrate [1]. Ge-on-Si epitaxy by low-energy plasma-enhanced CVD (LEPECVD), allows for controlling the microcrystal faceting, in turn affecting the evolution of threading dislocations and providing complete expulsion of threading arms to the microcrystal sidewalls [2]. In addition, the microcrystals are self-assembled in dense arrays, with a spacing ranging from tens to one hundred nanometers. The growth mechanism of the micro-crystals is an intriguing “nano” effect, which has been interpreted in terms of independent facet growth. This effect is not a unique feature of Ge deposition by LEPECVD, but a more general growth mode, which can be extended to other materials systems and deposition techniques. GaAs microcrystals deposited by MBE on patterned Si substrates show as well the complete tessellation of the surface by closely separated microcrystals. The complete elimination of thermal strain and reduction of threading dislocations is confirmed by the high photoluminescence yield. [1] C. V Falub et al. Science 2012, 335, 1330–4 ; [2] A. Marzegalli et al., Advanced materials 2013, 25, 4408