Wachstum und Charakterisierung von Aluminiumnitrid-Pseudosubstraten auf c -Saphir. Vergleich von konventionellem und gepulstem Wachstum mittels Metallorganischer Gasphasenepitaxie.

Abstract

In the last years, great progress has been made in the field of nitride based solid state lighting. Prominent examples are bright Gallium nitride (GaN) based LEDs emitting in the green and blue spectral region. Furthermore, light bulbs are increasingly replaced by white LEDs, which are by far more efficient. Also, solid state laser diodes based on Gallium nitride are available. By now, blue lasers are used for data storage in Bluray disk drives and enable a much higher density of data as compared to red diodes, which are used in CD and DVD drives. Green laser diodes will be available within the next few years and will allow for new applications like micro beamers and optical communication networks based on plastic fibers. The basis for all these applications are suitable optoelectronic devices, of which the quality depends on technological developments and the quality of the substrate, on which they are grown. In contrast to silicon, which is used for electronic devices, Gallium or Aluminium nitride (AlN) can not be produced from a melt, due to the high partial pressure of nitrogen. Indeed, pure substrates are available from special production methods, but these are very expensive. Hence nitrides are usually grown on substrates like sapphire or silicon carbide, which leads to challenges due to the difference in the lattice constant of substrate and layer material. The growth of AlN is further hindered by the high diffusion barriers for Al and N on the AlN surface. This leads to low lateral growth rates and thereby high dislocation densities. The goal of this work was the growth of AlN-templates on c-plane sapphire by metal organic vapor phase epitaxy. To increase the lateral growth rate two concepts are used. On the one hand a growth at high temperatures of 1250°C and on the other hand a pulsed growth mode at 1070°C, in which the precursors are supplied in separate time periods. For both methods, different parameters, concerning growth conditions and growth procedure, are investigated. Concerning the pulsed growth a different growth process is observed, resulting in a higher growth speed, when compared to the results published by other groups. By continuous growth we obtained AlN templates, of which the quality is quite comparable to the results of other groups. The samples are mainly characterized by high resolution X-ray diffraction and scanning electron microscopy but other methods are also used to determine the polarity and surface morphology. Special attention is paid to unusual X-ray rocking curves, which could lead to an underestimation of the crystal quality. After all, the shape could be explained by an alternative nucleation model.