Understanding the Role of the Low Temperature Seed Layer in the Growth of Low Defect Relaxed Germanium Layers on (111) Silicon by Reduced Pressure CVD

In this work, the role of the low temperature seed layer in more detail is discussed, by analyzing layers grown at a range of temperatures and as function of layer thickness with a combination of analysis techniques including high resolution TEM, atomic force microscopy (AFM) and X-ray diffraction (XRD). The aim of the LT seed is to accommodate all of the lattice mismatch, leaving the HT layer fully relaxed. In practice there is some residual compressive strain which, as the growth temperature is increased for the HT layers, can lead to island formation at the start of these HT layers. These Ge islands can act as sources for further dislocation nucleation and promote dislocation annihilation within their restricted volume. This influences both the dislocation network during the growth and the surface morphology of the final high temperature layer. However, the continued high temperature growth leads to a smoothing effect as the mobile dislocations annihilate and a smooth surface of less than 2 nm rms, although the threading dislocations can also dissociate into stacking faults for (111) oriented growth leading to surface steps.