Scanning tunneling microscopy and -spectroscopy of GaP layers on Si(001)

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Gallium phosphide based materials on silicon(001) substrates are promising for the integration of optoelectronic devices with the well-established silicon technology. The advantage of gallium phosphide compared with other III-V semiconductor materials is the low lattice mismatch to silicon. However, the growth of polar semiconductors on non-polar substrates results in the formation of domains with different polarities, which are separated by antiphase boundaries. An antiphase boundary is a stacking fault, which leads to neighboring atoms with the identical electron configuration. Thus, within gallium phosphide, phosphorous or gallium double bonds are formed, which are charged defects proceeding two-dimensionally within the crystal. Hence, the antiphase boundaries act as nonradiative recombination centers and lead to efficiency losses of the resulting devices. In the present project the structural and electronic properties of the antiphase boundaries and their influence on nano-structured samples shall be investigated using cross-sectional scanning tunneling microscopy and spectroscopy. In particular the GaP/Si(001) interface shall be imaged on the atomic scale and studied with respect to decomposition or segregation effects. The goal of those investigations is to achieve a physical understanding of the growth processes at the GaP/Si(001) interface as well as of the structural and electronical properties of defects within the gallium-phosphide layer. The results shall pave the way to avoid or to systematically annihilate the antiphase boundaries in order to increase the quality of the resulting GaP/Si(001) layer and the semiconductor structures grown on top.