Abstract
In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1–2 × 109 cm−2, which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 × 109 cm−2). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices.
Highlights
The use of epitaxial Alx Ga1 − x N alloys wide-band gap semiconductors have drawn increasing attention because of their potential expanding applications for ultraviolet (UV) optoelectronic devices and high-power, high-frequency electronic devices [1,2,3]
hydride vapor phase epitaxy (HVPE) is expected to permit the growth of thick AlGaN, which can possibly serve as pseudosubstrates to mitigate the lack of Materials 2017, 10, 605; doi:10.3390/ma10060605
A variety of hole dimensions for nano-imprinting were attempted, the optimum nanoscale-patterned sapphire substrate (NPSS) used in this study were with 500-nm-diameter hole array, spaced
Summary
The use of epitaxial Alx Ga1 − x N alloys wide-band gap semiconductors have drawn increasing attention because of their potential expanding applications for ultraviolet (UV) optoelectronic devices and high-power, high-frequency electronic devices [1,2,3]. UV optoelectronic devices significantly affects their internal quantum efficiency and operational lifetime due to the presence of heteroepitaxial-growth-induced defects (e.g., threading dislocations (TDs), stacking faults, voids, and point defects) [4,5]. Hydride vapor phase epitaxy (HVPE) has been shown to achieve rapid growth rates of several hundred micrometers per hour. Growth rates of approximately 30–50 μm/h have been reported for the growth of freestanding GaN substrates and AlN [6,7]. HVPE is expected to permit the growth of thick AlGaN, which can possibly serve as pseudosubstrates to mitigate the lack of Materials 2017, 10, 605; doi:10.3390/ma10060605 www.mdpi.com/journal/materials
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