Improved brightness of 380 nm GaN light emitting diodes through intentional delay of the nucleation island coalescence

Koleske, Daniel; Fischer, Arthur J.; Allerman, Andrew A.; Mitchell, Christine C.; Cross, Karen Charlene; Kurtz, S. R.; Figiel, Jeffrey J.; Fullmer, Kristine Wanta; Breiland, William G.

doi:10.1063/1.1506793

Cited by 130 publications

(91 citation statements)

References 16 publications

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“…Trapezoidal facet formation is enhanced during initial growth stage by a relatively low V/III ratio [21]. Density of high-temperature-grown nuclei tends to decrease by low V/III ratio, followed by lateral growth and bending of dislocations [22]. Lateral to vertical growth rate ratio seems smaller in case of the highest growth rate of 28 m=h, which resulted in a broader line width of (102) reflection.…”

Section: Results Of High-growth-rate Gan By Using a High-flow-speed Rementioning

confidence: 96%

High Growth Rate MOVPE

Matsumoto¹,

Tokunaga²,

Ubukata³

et al. 2010

Technology of Gallium Nitride Crystal Growth

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In this chapter, growth mechanism of GaN and AlGaN by MOVPE is described in detail. The parasitic reaction that generates particulates in vapor phase is the most probable limiting factor of maximum growth rate of GaN and AlGaN. Both experimental and quantum chemical study of vapor phase reaction between organo-metals and ammonia is described. From the close insight of vapor phase reaction, high flow speed three layered gas injection has been developed. By employing this three-layer gas-injection, GaN was grown with growth rate as high as 28m/h at atmospheric pressure. As long as the present growth conditions are concerned, SIMS and XRD results suggested that the growth rate of 12m/h would be a practical limitation of good quality material in terms of electrical and structural properties.

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Section: Results Of High-growth-rate Gan By Using a High-flow-speed Rementioning

confidence: 96%

High Growth Rate MOVPE

Matsumoto¹,

Tokunaga²,

Ubukata³

et al. 2010

Technology of Gallium Nitride Crystal Growth

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“…Also plotted are the binodal and spinodal phase separation calculated by Ho and Stringfellow [11]. ingly localized in In-rich quantum wells and the trapping of carriers at the abundant threading dislocations or other nonradiative recombination centers decreases [5]. However as the indium content increases to 15-20 % and the localization increases, these "quantum dot-like" structures may have increased defect structure, which will again increase non-radiative recombination leading to reduced light emission from the QWs.…”

Section: Status Of Ingan Growth For Green and Longer Wavelength Ledsmentioning

confidence: 99%

Issues associated with the metalorganic chemical vapor deposition of ScGaN and YGaN alloys.

Koleske¹,

Knapp²,

Lee³

et al. 2009

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We report on issues associated with the metalorganic chemical vapor deposition growth of ScGaN and YGaN. Based on the proposed bandgaps of ScN (2.15 eV), YN (0.8 eV) and the known bandgap of GaN (3.4 eV), we expected that LEDs could be fabricated from the UV (410 nm) to the IR (1600 nm), resulting in LED over all visible wavelengths for solid state lighting However, due to the low volatility of scandium and yttrium metalorganic precursors, we were only able to incorporate doping level concentrations of these atoms into a GaN film. This report highlights the difficulties encountered during the growth of these alloys and how some of these difficulities were overcome. We also investigated the nitridation of thin scandium metal films deposited on GaN using pulsed laser deposition. GaN was also grown on these thin ScN films to as a means to lower the GaN dislocation density. 4This page has been left intentionally blank 5 Extended AbstractThe most energy efficient solid state white light source will likely be a combination of individually efficient red, green, and blue LED. For any multi-color approach to be successful the efficiency of deep green LEDs must be significantly improved. While traditional approaches to improve InGaN materials have yielded incremental success, we proposed a novel approach using group IIIA and IIIB nitride semiconductors to produce efficient green and high wavelength LEDs.To obtain longer wavelength LEDs in the nitrides, we attempted to combine scandium (Sc) and yttrium (Y) with gallium (Ga) to produce ScGaN and YGaN for the quantum well (QW) active regions. Based on linear extrapolation of the proposed bandgaps of ScN (2.15 eV), YN (0.8 eV) and GaN (3.4 eV), we expected that LEDs could be fabricated from the UV (410 nm) to the IR (1600 nm), and therefore cover all visible wavelengths. The growth of these novel alloys potentially provided several advantages over the more traditional InGaN QW regions including: higher growth temperatures more compatible with GaN growth, closer lattice matching to GaN, and reduced phase separation than is commonly observed in InGaN growth. One drawback to using ScGaN and YGaN films as the active regions in LEDs is that little research has been conducted on their growth, specifically, are there metalorganic precursors that are suitable for growth, are the bandgaps direct or indirect, can the materials be grown directly on GaN with a minimal defect formation, as well as other issues related to growth.The major impediment to the growth of ScGaN and YGaN alloys was the low volatility of metalorganic precursors. Despite this impediment some progress was made in incorporation of Sc and Y into GaN which is detailed in this report. Primarily, we were able to incorporate up to 5x10 18 cm -3 Y atoms into a GaN film, which are far below the alloy concentrations needed to evaluate the YGaN optical properties.After a no-cost extension was granted on this program, an additional more "liquid-like" Sc precursor was evaluated and the nitridation of Sc metals on GaN w...

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“…For example, using reflectance we were able to control the NL thickness to within 29.81 ± 0.09 nm for 17 different NL growths. Our previous publication demonstrated how delaying the 3D to 2D recovery time reduced the dislocation density and lead to dramatic increase in near-UV LED output intensity [17]. More recently, we have used optical reflectance to measure the temperature dependent optical constants for sapphire, the GaN NL, and the bulk GaN film.…”

Section: Using Optical Reflectance To Monitor Gan Growthmentioning

confidence: 99%

“…5 are the various physical properties and changes to the GaN film morphology that can be measured using optical reflectance, which are shown in black, blue, and red lettering [6,16,17]. The film properties that are commonly measured by many researchers are shown in black, and include measurements of the NL thickness, the bulk growth rate, the 3D to 2D recovery time [17] and roughening [18]. For example, using reflectance we were able to control the NL thickness to within 29.81 ± 0.09 nm for 17 different NL growths.…”

Section: Using Optical Reflectance To Monitor Gan Growthmentioning

confidence: 99%

Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

Koleske¹,

Lee²,

Lemp³

et al. 2009

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With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growthenabled reductions in dislocation density would be highly prized.GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density.In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5x10 8 cm -2 using our standard delay recovery growth technique to 1x10 8 cm -2 using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined using optical reflectance and the nucleation density was determined using atomic force microscopy (AFM) and Nomarski microscopy. Dislocation density was measured using Xray diffraction and AFM after coating the surface with silicon nitride to delineate all dislocation types. The program milestone of producing GaN films with dislocation densities of 1x10 8 cm -2 was met by silicon nitride treatment of annealed sapphire followed by the multiple deposition of a low density of GaN nuclei followed by high temperature GaN growth. Details of this growth process and the underlying science are presented in this final report along with problems encountered in this research and recommendations for future work.

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Improved brightness of 380 nm GaN light emitting diodes through intentional delay of the nucleation island coalescence

Cited by 130 publications

References 16 publications

High Growth Rate MOVPE

High Growth Rate MOVPE

Issues associated with the metalorganic chemical vapor deposition of ScGaN and YGaN alloys.

Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

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