Hochaufgelöste transmissionselektronenmikroskopische Untersuchungen an Galliumphosphid auf Silizium

Andreas Beyer, Volz, Kerstin (Prof. Dr.), Physik
In this work GaP/Si-heterostructures, which were grown by MOVPE, were studied utilizing different TEM techniques. With the high-resolution HAADF technique one is capable of investigating interfaces as well as possible APDs on an atomic scale. Despite the commonly praised more intuitive interpretation in comparison to conventional TEM-measurements, effects beyond pure Z-contrast are observable, making an adequate simulation indispensable. It was shown that the AP-approximation deviates by less
more » ... deviates by less than 5% from the more time consuming FP-approximation for TEM-sample thicknesses below 50 nm. If relative intensities are evaluated instead of absolute ones, the AP-approximation is valid for an even wider range of thicknesses. The simulations show that the intensity-ratio of Si:Ga or P:Ga, respectively, is a good measure of the thickness of a sample. This facilitates the direct determination of the local thickness from experimental HAADF images. The influence of chemical intermixing on the HAADF intensity and the optimum detector size was determined by additional simulations at a fixed sample thickness. The Si-buffers grown on exactly oriented Si-substrates show, unlike theoretical predic-tions, a clear predominance of the A-type surface reconstruction, in which the dimers are oriented perpendicular to the step edges. This is caused by the H2-rich growth conditions, which significantly differ from the UHV conditions that were assumed to calculate the surface energies. The GaP-layers grown on these substrates always exhibit P-polarity viewed along the step edges. If this polarity is projected down to the interface, it is dominated by Ga-Si bonds. This is caused by the fact that the P-precursor (TBP) is not fully decomposed at the low growth temperatures and the Si-surface is passivated by hydrogen due to the prior buffer growth. O [...]
doi:10.17192/z2012.0905 fatcat:nbn4k3dl45darowxegktcj6ime