Defect reduction and efficiency improvement of near-ultraviolet emitters via laterally overgrown GaN on a GaN/patterned sapphire template

Abstract

An approach to improve the defect density and internal quantum efficiency of near-ultraviolet emitters was proposed using a combination of epitaxial lateral overgrowth (ELOG) and patterned sapphire substrate (PSS) techniques. Especially, a complementary dot array pattern corresponding to the underlying PSS was used for the ELOG-SiO2 mask design. Based on the transmission-electron-microscopy and etch-pit-density results, the ELOG/SiO2/GaN/PSS structure can reduce the defect density to a level of 10(5) cm(-2). The internal quantum efficiency of the InGaN-based ELOG-PSS light-emitting diode (LED) sample showed three times in magnitude as compared with that of the conventional GaN/sapphire one. Under a 20 mA injection current, the output powers of ELOG-PSS, PSS, and conventional LED samples were measured to be 3.3, 2.9, and 2.5 mW, respectively. The enhanced output power could be due to a combination of the reduction in dislocation density (by ELOG) and improved light extraction efficiency (by PSS). Unlike the previous double ELOG approaches, the presented ELOG-PSS structure needs only one regrowth process and will have high potential in future high-quality ultraviolet emitters, even blue/green laser diode applications. (c) 2006 American Institute of Physics

Optoelectronic Properties and Structural Characterization of GaN Thick Films on Different Substrates through Pulsed Laser Deposition

“…This presents a serious problem, as a high defect density and a large biaxial stress in the heteroepitaxy of the GaN epilayers are generated by mismatches in the lattice structure and thermal expansion coefficients between the epilayers and the Si substrate. These growth-induced defects (such as threading dislocations, stacking faults, voids, and point defects) limit the performance and reliability of GaN-based devices [4][5][6]. ZnO-related materials may be closely lattice-matched with GaN, but the drawback of the ZnO single crystalline wafer is that it is still expensive [7].…”

High Responsivity in GaN Ultraviolet Photodetector Grown on a Periodic Trapezoid-Column Patterned Sapphire Substrate

“…In recent years, it has been reported that the TD density can be reduced by growing a GaN film on a patterned sapphire substrate (PSS). (14,15) Unlike those in nitride LEDs with a conventional sapphire substrate, the nitride LEDs fabricated on a lamp-form PSS showed improved output power, external quantum efficiency, and reverse leakage current, as reported by Wuu et al (16) They attributed the improved results to the elimination of TDs and the enhancement of the extraction efficiency using the PSS.…”

Analysis of loss mechanisms in InGaN solar cells using a semi-analytical model

“…[11][12][13][14] Other optoelectronic devices have been more inclined to employ pattern sapphire substrates (PSS) to enhance light extraction. [18][19][20][21][22] Furthermore, despite costly and complicated growth and fabrication process, there have been reports proposing using diffraction grating on the back of the device for InGaN solar cells to enhance the optical absorption, 23 which combines the textured surface and reflecting substrate. These reports are also consistent with our findings here.…”