Microscopy study of extreme lattice mismatched heteroepitaxy using interfacial misfit arrays

The Sb-bearing compounds offer a wide range of electronic bandgaps, bandgap offsets and electronic barriers along with the extremely high electron mobility and therefore enable a variety of high speed, low power electronic devices and infrared light sources. Therefore, lattice-mismatched epitaxy of Sb-based materials on GaAs and Si substrates has attracted considerable attention. However, due to material growth issues such as large lattice mismatch, anti-phase domains and thermal expansion coefficient mismatch, the material relieves strain energy through misfit dislocations, defects and often threading dislocations, which vertically propagate to active regions of devices, thus leads to non-radiative recombination and damages device performance. The majority of the work done in this field has been focused on the interfacial misfit (IMF) array based growth mode between GaAs and GaSb, and AlSb on Si substrate. Since the formation of an IMF array does not proceed through the critical thickness method, but instead makes use of atomic arrangements on the surface of substrate to spontaneously relieve the high strain energy between the epi-layer and substrate. Thus this growth mode allows us to grow highly mismatched and low defect density epi-layer material. In this research, not only have we demonstrated that an IMF array can be formed to fully relieve strain energy at the compressive GaSb/GaAs interface, but also verified that an IMF array can be obtained in the tensile GaAs/GaSb interface once the reaction of the As2 with GaSb surface is suppressed. Meanwhile, the IMF growth mode has also been applied for obtaining high quality AlSb epilayers monolithically on 5° miscut Si (100) substrate. We attribute the success of AlSb growth on 5° miscut Si (100) surface to both the step doubling-atom mechanism in combination with the strong Al-Sb atomic bond. The AlSb bulk materials with low dislocation density and strain-relieved properties generated by the growth conditions can provide a promising technology for the monolithic integration of III-V devices on Si substrate. Finally, We have demonstrated the ability to control either an IMF or a Stranski-Krastanov (SK) growth mode to grow GaSb QDs on GaAs substrates by varying V/III ratio. A high V/III ratio such as 10:1 produces IMF growth mode, while a low V/III ratio of 1:1 favors SK growth mode