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Metal-organic vapour phase epitaxy (MOVPE) is the prevailing technology for mass fabrication for III-V-semiconductor heterostructures. Optical in-situ measurement techniques are becoming more and more crucial for the device developments and materials characterization during the growth. Although these measurement techniques are compatible with a MOVPE environment, e.g. typical pressures of 20-100 mbar and temperatures of 450°C - 1100°C, optical techniques using visible wavelength cannot reveal microscopic structures. Therefore, we have designed and built the first in-situ scanning tunnelling microscope (STM) capable of measuring topography with a vertical resolution smaller than 0.25 nm during the growth of nanostructures in MOVPE and up to temperatures of 700°C. In comparison to molecular beam epitaxy (MBE) where in-situ STMs already exist, STM operation during MOVPE must overcome additional challenges, like restricted space, mechanical noise from vibrations from the rotary pumps and electrical noise from a non-shieldable quartz reactor. To solve the heat problem, arising from the high thermal conductivity of the carrier gas (typically hydrogen at 100 mbar), we have designed an active cooling shield to keep the piezo temperatures below 100°C. Measurements proofed that the in-situ STM has no direct influences to the growth parameters. In addition to the discussion of the setup, we will show the first in-situ STM measurements of Ostwald-ripening of InAs quantum dots on a GaAs(001) surface. The quantum dots are grown with hydrogen carrier gas at 5 seconds with 0.5Pa TMIn (trimethylindium) and 5.0Pa tBAs (tertiarybutylarsine). After the growth of InAs quantum dots a sequence of in-situ STM images of 5x5µm2 were recorded over a range of 40 minutes at a sample temperature of 475°C with 5Pa tBAs stabilisation. Each image took 4.3 minutes. Three different structures (quantum dots, small and big clusters) could be differentiated by their size. During the Ostwald-ripening the smallest quantum dots vanished exponentially, while the density of the big clusters increased slightly. The density of the small size clusters was constant. |