Studies of the structural defects in gallium arsenide on silicon grown by molecular beam epitaxy

We have investigated structural defects (stacking faults and dislocations) in GaAs epitaxial layers grown on Si substrates by molecular beam epitaxy (MBE) with different growth conditions for the buffer layers and with a variety of strained layer superlattice (SLS) structures and thermally cycled strained layers grown between the buffer layer and overlayer regions. These layers were examined by transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and double crystal X-ray diffraction (DCXD).; Three different growth conditions were chosen for buffer layers, including; conventional growth at 300{dollar}sim{dollar}400{dollar}spcirc{dollar}C with a As{dollar}sb4{dollar}/Ga flux ratio of 20, growth with a reduced As{dollar}sb4{dollar}/Ga flux ratio of 7 at 400{dollar}spcirc{dollar}C followed by in-situ annealing, and very low temperature growth (90{dollar}spcirc{dollar}C) with in-situ solid phase epitaxy (SPE). The latter two processes resulted in significant improvements of surface morphology of buffer layers. This surface smoothness of initial buffer layers significantly reduced the stacking fault density. From this, we suggest a new mechanism for stacking fault formation at surface notch regions due to the glide of pure-edge partial dislocations in highly strained epitaxial film growth. The dislocation density in the overlayers also exhibited a much stronger dependence on the growth conditions for the GaAs buffer layers than the magnitude of strain energy in the SLSs.; Alternative strained layers grown with in-situ thermal cycling were utilized to suppress threading dislocation density in the GaAs layers. These samples showed much improved crystalline quality and dislocation density compared to the conventionally grown ones.; We have carried out kinetic nucleation model calculations in order to estimate the activation energies for two kinds of half-loop dislocations; 60{dollar}spcirc{dollar} perfect dislocations and pure-edge partial dislocations. We also suggest a simple model for stacking fault stability. The results of these calculations showed that pure-edge partial dislocations play an important role in relaxing the misfit strain at the initial stages of growth by nucleating stacking faults in the GaAs epilayer. The morphology and distribution of stacking faults observed by cross-section TEM also coincides with this analysis.