Structural properties of aluminum nitride bulk single crystals grown by PVT

Schimmel

et al. 2011

Phys. Status Solidi C

Structural defects in aluminium nitride (AlN) get visible in panchromatic cathodoluminescence (CL) maps as luminescence at 340 nm and 630 nm is locally enhanced. Low‐angle grain boundaries (LAGBs) and dislocations can be detected as long as they are sufficiently decorated and the defect‐related contrast is higher than local variations in background CL intensity. We applied the method to c ‐plane and a ‐plane cuts of one of our off‐oriented grown AlN crystals and describe occurrence, routes, and dissolution into dislocation bunches of LAGBs. We found that the vast majority of LAGBs are uneven a ‐planes which extend in a preferential m ‐ as well as in c ‐direction. As a consequence, their density decreases only slightly during growth. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Section: Lagb Evolution In Aln Bulk Crystalssupporting

confidence: 79%

mentioning

confidence: 99%

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Structural defects in aluminium nitride bulk crystals visualized by cathodoluminescence maps

Schimmel

et al. 2011

Phys. Status Solidi C

“…AlN-on-SiC templates [9] with the SiC part removed as well as bulk AlN substrates are used as seeds. For some of the crystals (most of them grown on bulk AlN substrates), multiple resublimation of the source material prior to growth was employed in order to further reduce oxygen contamination.…”

Section: Methodsmentioning

confidence: 99%

UV transparent single‐crystalline bulk AlN substrates

Phys. Status Solidi (c)

Filip

et al. 2010

Bulk aluminum nitride (AlN) is a very promising substrate material for UV optoelectronics, and its UV transparency is of high interest for UV devices designed to emit through the substrate. We report on 500 μm thick bulk AlN substrates with plain UV transmittance exceeding 50% (i.e., absorption coefficients below 14 cm–1) for wavelengths from 220 nm to 380 nm in the main wafer area. Comparing the spectra of different AlN bulk samples, four major below band‐gap absorption bands are identified and interpreted based on a point defect model for AlN crystals. We conclude that a further reduction of oxygen contamination of the source material led to a significant decrease of UV absorption in both colorless and yellowish areas of those substrates. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

“…sublimation and recondensation of an AlN charge placed in a tungsten crucible, as reported earlier. For this study, spontaneously nucleated free-standing crystals [9] as well as crystals seeded on AlN templates [10] are cut into wafers, which are then polished on both faces. As evidenced by mass spectrometry and inert gas fusion, oxygen content is about 100 ppm wt; all other impurities except carbon (and possibly hydrogen) are well below 2 ppm wt.…”

mentioning

confidence: 99%

Point defect content and optical transitions in bulk aluminum nitride crystals

Physica Status Solidi (b)

Filip

et al. 2009

Different zones of nominally undoped AlN bulk single crystals are investigated using optical absorption and cathodoluminescence. Incorporation of impurities and formation of intrinsic defects during growth strongly depend on the facet which forms the zone. Following first principles calculations and earlier observations on AlN epilayers, we assign the endpoints of the observed optical transitions to ionization levels of oxygen, VAl2–/3–, and (VAl–ON)–/2–. According to the strength of the respective optical transitions in different zones, we find that oxygen contamination increases in the order Al‐polar (0001), rhombohedral {10$ \bar 1 $2} and prismatic {10$ \bar 1 $0}, N‐polar (000$ \bar 1 $). We conclude that the low UV transmittance typically observed in bulk AlN is caused by the formation of VAl and (VAl–ON). These deep levels form in the presence of oxygen, which is the major contaminant in bulk AlN. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)