Gallium nitride (GaN) is a wide-band-gap semiconductor material, which is used for the production of light emitting devices and LASER diodes. Presently, nearly all GaN devices are manufactured on so-called GaN-templates. These templates are made e.g. by MOCVD deposition of GaN onto a sapphire or SiC substrate. In order to obtain a superior quality and performance of the device, substrates with lower defect density are required.

One way to produce such low-defect substrates is the Liquid Phase Epitaxy (LPE). Our LPE process is performed at ambient pressure and differs from classical LPE by the fact that one component of the grown material, i.e. the nitrogen, is not included in the solution itself from the beginning, but supplied during the process via the gas atmosphere in form of ammonia. To distinguish our process from the classical LPE technique we call it Low Pressure Solution Growth (LPSG) technique.

Details of the LPSG process will be presented. Especially the influence of the ammonia partial pressure and the temperature on the formation of epitaxially and parasitically grown GaN will be addressed, leading to the determination of a kind of Ostwald-Miers region. The growth of parasitical GaN is considered to be the limiting factor for the maximum achievable process time as well as for the growth rate of the epitaxial GaN, which is a main drawback of the method. However the quality of the epitaxial layer as well as the total process time is enhanced by applying process parameters suppressing parasitical GaN growth.

Additionally the growth mechanism of the epitaxial layer is a great benefit of the method. During heating of the solution the GaN seeding layer is etched back due to the lack of dissolved nitrogen. After saturation of the solution, growth process starts by the formation of oriented islands. During this initial growth state a considerable reduction of the dislocation density takes place. By TEM observations it was proven that the typical dislocation density of the MOCVD seeding layer was reduced by at least one order of magnitude to about 10⁸ cm^-2 within 1 µm of LPSG layer thickness. Within this first micrometer the coalescence of the LPSG islands is completed and a continuous GaN layer is formed across the whole wafer diameter.

With the LPSG technique it is possible to produce GaN templates with 3 inch diameter and various layer thicknesses (e.g. from 1 to 40 µm). The growth process can easily be applied for larger diameter templates as well as for multi-wafer-processes, mainly determined by the dimensions of the reactor.

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