Synchrotron X-Ray Diffraction Topography of Semiconductor Heterostructures

In this thesis dislocations, other crystal defects, and strain in compound heterostructures were studied by means of synchrotron radiation X-ray topography and other X-ray methods. Also, models for critical thickness of thin films were compared to experimental results. Synchrotron radiation X-ray topography (SR-XRT) is an ideal method for studying strained heterostructures with relatively few dislocations (<104 cm2). Crystal defects in GaAs ans InAs p-i-n structures were characterized. Misfit dislocations and critical thickness in epitaxial dilute GaAsN on GaAs was characterized with synchrotron radiation X-ray topography and high-resolution X-ray diffractometry. Defect structure of thin GaAs epitaxial layer on Ge substrates was studied. Strain distribution between GaN thin films and sapphire substrate was analyzed from back-reflection synchrotron X-ray topographs, and cellular network of strain with about 30 micrometer cell size was discovered. Epitaxial quality of the GaN layers was analyzed. InP epitaxial lateral overgrowth layers were analyzed with synchrotron radiation X-ray topography and high-resolution X-ray diffraction, and strain fields around the growth window edges were successfully imaged. Reciprocal space maps (RSM) were measured from GaInP on GaAs buffer on Ge substrate heterostructures, and no relaxation was observed in neither sample, which proves that a very small number of misfit dislocations is only detectable with SR-XRT. Critical thickness models were compared with experimental data for the GaInP thin film on GaAs buffer on Ge substrate heterostructure, and new insight was found about the relation of pyramidical hillock defects to misfit dislocation formation. Also, the crystal structure of the pyramidical hillocks was determined, and it was found that they are composed of InP instead of GaInP as previously thought. The critical thickness model was successfully expanded to take thermal expansion into account.The information about crystal defects and their distribution, and analysis methods to study them, which was acquired in this thesis, can be used to better understand and control crystal defects in semiconductor heterostructures.