Abstract
To exploit unique properties of thin films of group III-nitride semiconductors, the production of native substrates is to be developed. The best choice would be AlN; however, presently available templates on sapphire or SiC substrates are defective. The quality of AlN could be improved by eliminating the substrate during the layer growth. In this paper, we demonstrate freestanding AlN layers fabricated by an SiC substrate evaporation method. Such layers were used to investigate dislocation structures near the former AlN–SiC interface. Specimens were characterized by synchrotron radiation imaging, triple-axis diffractometry and transmission electron microscopy (TEM). We found that the evaporation process under non-optimal conditions affected the dislocation structure. When the growth had been optimized, AlN layers showed a uniform distribution of dislocations. The dislocations tended to constitute low-angle subgrain boundaries, which produced out-of-plane and in-plane tilt angles of about 2–3 arc-min. Similar broadening was observed in both symmetric and asymmetric rocking curves, which proved the presence of edge, screws as well as mixed dislocation content. TEM revealed arrays of edge threading dislocations, but their predominance over the other threading dislocations was not supported by present study. To explain the experimental observations, a theoretical model of the dislocation structure formation is proposed.
Highlights
The III–V nitride semiconductors have been having a growing impact on device optoelectronics.The impact areas include optoelectronic devices in the visible short-wavelength region such as ultraviolet (UV) light-emitting diodes (LEDs), lasers and photo detectors
We investigate aluminum nitride (AlN) layers grown by physical vapour transport (PVT) on C-face silicon carbide (SiC) substrates using a substrate evaporation method [13]
Freestanding AlN layers were fabricated by an SiC substrate evaporation method
Summary
The III–V nitride semiconductors have been having a growing impact on device optoelectronics. The impact areas include optoelectronic devices in the visible short-wavelength region such as ultraviolet (UV) light-emitting diodes (LEDs), lasers and photo detectors. In LED technology, the III–V nitride films are grown by epitaxial techniques on foreign substrates, such as silicon, sapphire and silicon carbide (SiC). The lack of large-area native substrates of high crystalline quality that are lattice matched, chemically compatible and have a similar coefficient of thermal expansion remains a critical. Aluminum nitride (AlN) crystals are the most promising substrate materials for the semiconductor and UV LED industry [1,2]. AlN substrates usable for devices are fabricated from boules with diameters between
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