Homoepitaxial growth of high structural quality and high-purity thick gallium nitride layers by crystallization from vapor phase (hydride vapor phase epitaxy (HVPE)) on 1, 1.5, and 2 inch substrates obtained by a solution (ammonothermal) growth method is presented. Advantages and disadvantages of both growth technologies are described in detail. Structural, optical, electrical, and thermal properties of gallium nitride grown from the vapor phase are demonstrated and compared to properties of ammonothermally grown material. It is shown that a synergy of these two methods can create new opportunities for an efficient production of bulk gallium nitride crystals and then substrates. It is also shown that free-standing (products of slicing procedures) gallium nitride crystals obtained from growth by vapor phase on ammonothermal substrates can be successfully used as seeds for the next growth process by both discussed methods. Factors limiting HVPE and making it a ‘wafer to wafer’ technology are presented, clarified, and analyzed. Intentional introduction of silicon to growth of gallium nitride by HVPE and crystals with a high free carrier concentration and high structural quality are demonstrated. First electronic and optoelectronic devices fabricated on the free-standing gallium nitride substrates are shown.

Perspectives about growth of bulk gallium nitride crystals, fabricating high structural quality gallium nitride wafers and the market demand for them are presented. Three basic crystal growth technologies, halide vapor phase epitaxy, sodium flux, and ammonothermal, are described. Their advantages and disadvantages, recent development, and possibilities are discussed. The main difficulty with crystallization of thick GaN is determined. Some new solutions for bulk growth are proposed. It is shown that only crystallization on high structural quality native seeds will ensure proper progress. New ideas for fabricating gallium nitride crystals and wafers with a better control of their structural properties and point defect concentration are proposed.

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

Crystallization of GaN by hydride vapor phase epitaxy (HVPE) on ammonothermally grown GaN seed crystals is described. The initial growth conditions for HVPE are determined and applied for further bulk growth. Smooth GaN layers up to 1.1 mm thick and of excellent crystalline quality, without cracks, and with low dislocation density are obtained. Preparation of the free-standing HVPE-GaN crystal by slicing and structural and optical quality of the resulting wafer are presented.

X-ray topography defect analysis of entire 1.8-inch GaN substrates, using the Borrmann effect, is presented in this paper. The GaN wafers were grown by the ammonothermal method. Borrmann effect topography of anomalous transmission could be applied due to the low defect density of the substrates. It was possible to trace the process and growth history of the GaN crystals in detail from their defect pattern imaged. Microscopic defects such as threading dislocations, but also macroscopic defects, for example dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls and dislocation bundles, were detected. Influences of seed crystal preparation and process parameters of crystal growth on the formation of the defects are discussed.