Structural and Optical Properties of GaAs Epilayers Grown on Si
Date Issued
2011
Date
2011
Author(s)
Hou, Ji-Ling
Abstract
In this thesis, we study the surface topography of silicon and its effects on the structural and optical properties of GaAs grown on Si. In the first part of this study, we used Scanning Tunneling Microscopy to investigate the Si surfaces with and without the treatment of Cl-based plasma. For surfaces without treatment, we observed that exact (001) Si surface contains only single-atomic-height steps with alternating SA and SB steps, while the vicinal Si (001) shows a dominance of biatomic-height steps (DB) accompanied with high density of single-atomic-height kinks. For the exact (001) surface with the treatment of Cl-based plasma, significant reduction of SB terrace was observed. The SB to SA terrace-area ratio is only 14% : 86%. The reduction of SB terrace makes the steps very similar to double-A steps (DA), which could open an alternative approach for anti-phase boundary (APB)-free III-V/Si growth.
In the second part of this study, the structural and optical properties of GaAs epitaxial layer on Si were investigated. From low temperature photoluminescence (PL), X-ray diffractometry (XRD) and Raman scattering, we observed a residual tensile strain resulting from the thermal expansion coefficient mismatch between GaAs and Si. The strain determined from above measurement is 2.19x10-3 at 12K and 1.5x10-3 at 300K, which is consistent to our theoretical calculation. For GaAs grown on exact (001) Si, we observed two types of anti-phase domains (APDs) with ripples along [110] and [1-10] orientation, respectively, from SEM viewgraphs. These two type APDs are interlaced on the surface. For the sample with the Cl-based treatment, one of the APD types dominates over the other one in terms of surface area, suggesting the improvement on APB problems with the treatment. By comparing the PL inner-band of the samples, we found that APBs act as nonradiative recombination centers to suppress the PL intensity and prevent the inter-diffusion of Si atoms into GaAs. In additions, from the results of Raman scattering and XRD, APBs enhance the forbidden TO mode, degrades the intensity XRD (004) reflection, which could be attributed to the structural disordering induced by APBs. We also used micro-Raman and cathodoluminescence (CL) to probe the boundaries of APDs and found a frequency downshift in Raman scattering and a red shift in CL, implying the existence of a uni-axial strain along the boundaries. In additions, we also observed the expected decrease of XRD (002) reflection in samples with APDs.
Subjects
Heteroepitaxy
GaAs
Si surface
Antiphase boundary.
Type
thesis
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