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Abstract: The direct growth of GaN by liquid phase epitaxy (LPE) on different AlN substrate orientations is demonstrated for the first time. The objective of this work was to study the seeding behaviour and morphology of GaN grown on different crystallographic orientations of the AlN substrate. Furthermore the incorporation of solvents and impurities in the epitaxial GaN was analysed. The surface treatment of the AlN-substrates before epitaxial growth turned out to be a challenging process, due to the fact, that polishing of the substrates is not yet developed in sufficient quality. Therefore, the aspect of surface treatment is addressed in brief. It was found that the growth of completely closed layers of GaN on Al-polar c-facets appears to be quite difficult compared to the formation of closed layers on N-polar c- and on r-facets. The growth of a closed GaN layer on single crystalline r-plane AlN substrates using the LPE technique could also be demonstrated. Characterisation by cathodoluminscence spectroscopy indicates that aluminium is incorporated with different content depending on the orientation. [Copyright &y& Elsevier]

Abstract: The features of solution growth at low pressure (LPSG) for single crystalline GaN are reported. The influence of important process parameters, especially the growth temperature T g and the partial pressure of the nitrogen supplying ammonia p(NH3) on thermodynamic and kinetic aspects of the growth process and on the resulting crystal properties are investigated. It is presented how the growth rate of the LPSG layer and the formation of parasitically grown GaN depend on T g and p(NH3). A kind of Ostwald–Miers diagram is derived which shows the T–p(NH3) regions of the best conditions for the growth of GaN by the LPSG method. It is demonstrated that 3 inch GaN templates can be grown successfully by using such LPSG process parameters. [Copyright &y& Elsevier]

Abstract: This work presents an experimental study on the identification and quantification of different types of dislocations in GaN grown by low-pressure solution growth. A reliable defect selective etching procedure in a NaOH-KOH melt is developed and validated using transmission electron microscopy that permits to define groups of etch pits that belong each to dislocations with a specific Burgers vector. This way a comparably fast method is provided for determining the total, the specific dislocation densities and the type of dislocation in a statistically representative way. The results for the solution grown samples are compared to those obtained for MOCVD GaN. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on a new simple method for avoiding particle-induced macroscopic defects using the liquid phase epitaxy (LPE) of GaN as an example. In a series of growth experiments by LPE of GaN it is demonstrated that the number of particle-induced macrodefects in the epitaxial layers correlates strongly and reproducibly with the density of the solution. In solutions with a density higher than that of the deleterious particles, the particles float on the solution and hence are hindered to get into contact with the seed, which is placed at the bottom of the crucible. Consequently, so-called depressions — a typical particle-induced defect in GaN–LPE layers — are avoided. The principle of avoiding the formation of macroscopic defects originating from particles by adapting the density of the solution (density criterion) should be generally applicable to solution growth processes, regardless of the material system. [Copyright &y& Elsevier]