Thesis (M.Eng)--Chulalongkorn University, 2010

GaAs is grown on Ge substrates by Molecular Beam Epitaxy (MBE) based on the fact that GaAs and Ge are lattice-matched materials. However, GaAs is a III-V compound semiconductor. When GaAs is grown on group IV Ge substrates, the anti-phase domain (APD) occurs due to randomness of group III and group V atoms grown as the first atomic layer at different seeding positions on Ge substrates. We investigate the growth conditions to obtain the large domains of GaAs epitaxial layer on Ge substrates. Migration-enhanced epitaxy (MEE) is used in our growth process. InAs QDs are grown on GaAs/Ge substrates having anti-phase domains (APDs). InAs QDs align in the specific crystallographic direction for each domain. The morphology of GaAs on Ge substrates is observed by atomic force microscopy (AFM). Large domain size of GaAs can be obtained by varying the GaAs thickness. TEM images of GaAs on Ge samples are also investigated. The defects at the domain interfaces are observed. The crystal quailty of GaAs is studied by X-ray diffraction (XRD) method. Ohmic contacts and Schottky contacts to GaAs on Ge samples are prepared by the thermal evaporation. The I-V characteristics of the samples are measured showing resistive combined materials while another samples act as a photodetector. Photoconductivity measurements of GaAs on Ge samples are conducted to study their spectral responses. Photoluminescence (PL) of GaAs grown on Ge substrates is investigated. PL result does not show any emission peaks from InAs QDs.