Lateral overgrowth of patterned c-plane oriented sapphire substrates (PSS) with AlGaN using hydride vapor phase epitaxy was investigated with focus on how to suppress parasitic non c-planar crystallite nucleation and propagation. To this end, trigonal PSS was fabricated with either sidewalls parallel to sapphire { 1 1 ¯ 00 } -facets or parallel to sapphire 1 ¯ 100 -facets, which are crystallographically different due to the three-fold sapphire symmetry. X-ray diffraction-based texture analysis and SEM were applied to find two types of 0001 A l G a N ∥ ( 11 2 ¯ 0 ) s a p p h i r e -domains solely nucleating on PSS sidewalls close to 1 ¯ 100 -facets. Their occurrence effectively blocks other orientations of non c-plane AlGaN crystallites allowing for quicker coalescence of c-plane AlGaN and improving overall AlGaN material quality.

Aluminum nitride growth via hydride vapor phase epitaxy has been investigated with respect to impurity uptake. The precursor aluminum chloride was identified to react with quartz glass and provide silicon into the reactor atmosphere and subsequently into grown AlN layers. Reactor parts made of quartz were consecutively replaced by carbon glass parts to prevent unintentional silicon incorporation into III-nitride layers during growth. Carbon glass substitution of quartz parts led to a reduction of silicon levels in AlN by three orders of magnitude to 4*10(16) cm(-3), while carbon concentration in grown AlN layers remained low in the range of 10(17) cm(-3).

To the end of improvement of layer morphology and crystalline perfection of thick AlGaN layers grown by hydride vapor phase epitaxy (HVPE) as well as for the suppression of crystallite formation during growth, the impact of AlN buffer layer properties on AlGaN growth was investigated. While the surface morphology of 500 nm thick AlN layer improves with higher V/III ratio toward 50 and lower growth temperatures of 1020 °C, its use as a buffer layer for thick AlGaN layers leads to strong degradation of AlGaN surface and even to formation of different crystallites during growth. Best surface morphology and crystalline perfection of thick AlGaN layers was observed for the growth on an AlN buffer layer with a higher crystal quality disregarding its 3D morphology and high surface roughness. Best results were achieved at medium V/III ratio of about 10–20 and AlN buffer growth temperature of 1060 °C.

AlGaN growth by hydride vapor phase epitaxy on patterned sapphire substrates has been investigated. Growth on honeycomb-shaped holes is disturbed by parasitic growth of c-plane oriented AlGaN crystallites on n-plane sapphire facets. Triangular hole-like structures allow for complete suppression of parasitic c-plane oriented AlGaN crystallites and coalescence of c-plane AlGaN at very low layer thickness. Additionally, triangular columnar sapphire patterns allow for biaxial strain relaxation and higher crystalline perfection. A total pressure of 400hPa is favored for lateral overgrowth of ternary AlGaN by hydride vapor phase epitaxy. Lower pressures lead to strong composition inhomogeneity and higher pressure to lower crystal perfection. Additionally, very low V/III ratios of less than 10 yield best results. Lower ammonia supply support the growth of beneficial {11-22}-AlGaN crystallites on sapphire m-sidewalls which supresses undesired AlGaN growth on sapphire n-facets.[GRAPHICS]. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Thick AlxGa1−xN layers were grown by hydride vapor phase epitaxy on hexagonally patterned sapphire substrates. Non-c-planar growth is found inside the etched honeycombs which in part hinders coalescence of the c-plane AlGaN layer growing on top of the ridges. From X-ray diffraction, electron backscatter diffraction and scanning electron microscopy, the orientations of the parasitic crystallites were identified as {11–22} and {1–103} AlGaN growing on m-plane sapphire sidewalls as well as c-plane oriented AlGaN growing on n-plane sidewall facets which are located in the corners of the combs. According to the geometry of parasitic crystallites, it is further observed, that the semipolar growth occurring on sapphire m-plane sidewalls does not hinder the coalescence of c-plane AlGaN growing on top of the ridges, whereas fast propagation of parasitic crystallites nucleating on n-plane sidewall facets leads to delayed layer coalescence.

Growth of Al x Ga1−x N layers by hydride vapor-phase epitaxy on patterned sapphire substrates is investigated. The pattern consists of honeycombs which by their orientation and size promote the formation of coalesced c-plane-oriented Al x Ga1−x N layers with reduced crack density. The orientation of parasitic crystallites in the honeycomb openings is investigated using scanning electron microscopy and electron back-scatter diffraction. Crystallites with their [\( \bar{1} \) \( \bar{1} \).0] and [52.3] directions parallel to the vertical growth direction of the Al0.3Ga0.7N layer are observed and successfully overgrown by a 20-μm-thick fully coalesced c-plane-oriented layer.