Patterning of sapphire/GaN substrates

Abstract

We present the results of sapphire/GaN substrate patterning on GaN film quality and on LED performance. MOVPE was used to grow GaN films on c‐plane sapphire. The films were then patterned with hexagonal holes with various diameters. When regrown with GaN, voids were formed in the sapphire/GaN interface. The void shape could be controlled from nearly vertical to inclined by changing the pattern dimensions. Patterning resulted also in reduced dislocation density of the overgrown GaN film. X‐ray diffraction and transmission electron microscopy results showed that the reduction is due to bending of edge‐type dislocations during the regrowth of the patterned substrate. Standard LEDs were grown on reference and patterned substrates and processed into chips. When grown on a patterned substrate LED chips showed approximately 10% increase in light output when compared to ones grown on a reference sample. The increase was attributed to improved light extraction. More improvement can be expected by optimizing the pattern geometry and the void shape. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

X‐ray reflectivity method for the characterization of InGaN/GaN quantum well interface

“…X‐ray reflectivity (XRR) is a powerful technique for thin film characterization () which is generally employed to determine the thickness of QWs . However, it can also be used to extract information relative to the interface of thin layers .…”

Temperature invariant energy value in LED spectra

“…9 The blue LED structure consisted of a sapphire wafer, a Si-doped n-GaN layer, a single InGaN/GaN quantum well, and a magnesium doped p-GaN layer. 10 Ti/Al/Au metal scheme was used for n-and p-metal contacts. The processed wafer was polished and diced into individual LED chips and then bonded onto silver-coated TO (transistor outline) headers to perform the measurements.…”

“…The blue InGaN/GaN LEDs manufactured by Aalto University were grown using metalorganic vapour phase epitaxy reactor, 10 and the alloy decomposition of the LEDs was known to be approximately In 0.15 Ga 0.85 N. For the In x Ga 1-x N alloy, the composition dependent band gap at T ¼ 0 K is given by 1 E g ðxÞ ¼ xE g;InN þ ð1 À xÞE g;GaN À bxð1 À xÞ;…”

Diffusion-Driven Charge Transport in Light Emitting Devices

“…The SAG of arsenide and phosphide III-V materials has been analyzed quite extensively and utilized as a major method for nanowire growth [52][53][54]. In III-N technology, SAG has been employed mostly in epitaxial lateral overgrowth (ELOG) methods which were developed to reduce threading dislocations in heteroepitaxial growth [55][56][57]. In contrast with ion implantation, the extensively characterized [58][59][60][61][62] defect-free GaN layers grown by lateral epitaxial over-growth can provide a more beneficial solution to realize LHJ structures [63].…”