No abstract

No abstract

First experimental results on the growth of GaN films by a modified high temperature vapor phase epitaxy method (HTVPE) are presented. The method bases on a novel growth reactor, which was developed to overcome the drawbacks of conventional HTVPE. GaN films were deposited either on (0001) sapphire substrates or on MOVPE‐grown GaN templates of 15×15 mm2 with growth rates in the range of 2–7 µm/h. The influence of the substrate temperature and ammonia flow on the structural properties of the deposited films was systematically investigated in experiments on MOVPE templates. It is shown that the structural quality of the templates can be well reproduced in the overgrown layers. The layer quality and the stress relations are found to depend very sensitively on the ammonia flow in the carrier gas. Growth experiments with a direct, high‐temperature deposition of GaN films on sapphire demonstrated a strong dependence of the nucleation process on the substrate temperature and the carrier gas composition. The potential of HTVPE for the heteroepitaxial growth of GaN films on sapphire is discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

The high temperature vapor phase epitaxy (HTVPE) uses ammonia and thermally evaporated, elemental gallium as precursors for the growth of GaN films. This paper investigates the HTVPE using numerical modeling of the gallium vapor transport and systematical growth experiments. The presented growth setup allows a flexible control of the growth process and variation of growth parameters in a wide range. Based on simulation results, the impact of the gallium melt temperature, the gas flow in the reactor and the reactor pressure on the gallium vapor transport is studied in detail. Experimental growth rates as function of the reactor pressure and the melt temperature are compared with the numerical simulation. The influence of hydrogen in the carrier gas on the properties of the HTVPE GaN layers is discussed.