Enhanced GaN decomposition in H2 near atmospheric pressures

Koleske, Daniel; Wickenden, A. E.; Henry, R.L.; Twigg, M. E.; Culbertson, James C.; Gorman, R. J.

doi:10.1063/1.122354

Cited by 83 publications

(61 citation statements)

References 20 publications

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“…Liquid Ga droplets were considered to act as a catalyst for GaN decomposition 14 and were found to be correlated with the GaN decomposition enhancement observed in H 2 near atmospheric pressure. 15 Furthermore, given that the absolute value of the GaN decomposition rate approaches the N-limited GaN growth rate ͑i.e., 5.0 nm/min͒ at 810°C, this temperature marks an upper limit for the successful growth of GaN for this fixed nitrogen flux and if exceeded results in thermal etching. It is therefore expected that higher active nitrogen fluxes will increase the Ga incorporation rate and thus enable growth at even higher temperatures.…”

Section: Discussionmentioning

confidence: 99%

In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction

Fernández-Garrido¹,

Koblmüller²,

Calleja³

et al. 2008

Journal of Applied Physics

103

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Thermal decomposition of wurtzite ͑0001͒-oriented GaN was analyzed: in vacuum, under active N exposure, and during growth by rf plasma-assisted molecular beam epitaxy. The GaN decomposition rate was determined by measurements of the Ga desorption using in situ quadrupole mass spectrometry, which showed Arrhenius behavior with an apparent activation energy of 3.1 eV. Clear signatures of intensity oscillations during reflection high-energy electron diffraction measurements facilitated complementary evaluation of the decomposition rate and highlighted a layer-by-layer decomposition mode in vacuum. Exposure to active nitrogen, either under vacuum or during growth under N-rich growth conditions, strongly reduced the GaN losses due to GaN decomposition.

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Section: Discussionmentioning

confidence: 99%

In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction

Fernández-Garrido¹,

Koblmüller²,

Calleja³

et al. 2008

Journal of Applied Physics

103

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“…For GaN substrates, it was found that the GaN surface is vulnerable to H 2 etching in the MOCVD ambient [52]. A layer-by-layer etching mode is rather difficult to achieve, likely due to large difference of the partial vapor pressure of surface N and Ga atoms [53].…”

Section: Substrate Pretreatmentmentioning

confidence: 99%

MOCVD growth of GaN-based high electron mobility transistor structures

Chen¹

2015

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IICover: surface morphology of a GaN high electron mobility transistor structure grown on a native GaN substrate. The image was obtained with an atomic force microscope. AbstractWide bandgap group-III nitride semiconductors like GaN, AlN, and their alloys are very suitable for the use in high-power, high-frequency electronics, as a result of their superior intrinsic properties. The polarization-induced high-density and high-mobility two-dimensional electron gas (2DEG) forming in (0001) oriented AlGaN/GaN heterostructures enable the epitaxial structure to be utilized for high electron mobility transistors (HEMTs). Outstanding power handling and record high frequency have been demonstrated from GaN-based HEMT devices over time. However, the shortterm stability and the long-term reliability of the device performances remain problematic. In order to make GaN HEMT technology truly take off and breach the civilian market like automotive, telecommunication applications, the problems need to be solved to justify its relatively high cost over the solutions based on Si and GaAs technologies.At the material level, there are two major challenges; one is the reduction of highdensity structural defects in heteroepitaxially grown layers when foreign substrates are used, and the other is the control of "deep" electron traps forming in the middle of the "wide" bandgap by intrinsic defects or extrinsic impurities.The main idea of the present work was therefore to tackle these material issues directly, using an approach called bottom-to-top optimization to improve the overall quality of GaN-based HEMT epitaxial structures grown on semi-insulating (SI) SiC and native GaN substrates. The bottom-to-top optimization means an entire growth process optimization, from in-situ substrate pretreatment to the epitaxial growth and then the cooling process. Great effort was put to gain the understanding of the influence of growth parameters on material properties and consequently to establish an advanced and reproducible growth process. Many state-of-the-art material properties of GaNbased HEMT structures were achieved in this work, including superior structural integrity of AlN nucleation layers for ultra-low thermal boundary resistance, excellent control of residual impurities, outstanding and nearly-perfect crystalline quality of GaN epilayers grown on SiC and native GaN substrates, respectively, and record-high room temperature 2DEG mobility obtained in simple AlGaN/GaN heterostructures.The epitaxial growth of the wide bandgap III-nitride epilayers like GaN, AlN, AlGaN, and InAlN, as well as various GaN-based HEMT structures was all carried out in a hot-wall metalorganic chemical vapor deposition (MOCVD) system. A variety of structural and electrical characterizations were routinely used to provide fast feedback VI for adjusting growth parameters and developing improved growth processes, such as optical microscopy (OM), atomic force microscopy (AFM), x-ray diffraction (XRD), capacitance-voltage measurement (CV) as well as sheet resistance...

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“…The differences in prefactors suggests that in addition to overall nucleation density the growth conditions also play an important role in dislocation reduction. Some of these factors may include preventing additional nucleation on the sapphire by increasing the growth pressure to induce higher GaN decomposition rates [6,14] and increasing the smoothness of the starting substrate to produce grains with improved orientation. Using etched mesas and a SiC growth step, SiC surfaces were generated that contained either atomically smooth mesas with no steps or mesa with regular step arrays [15].…”

Section: Correlation Between Nucleation and Dislocation Densitymentioning

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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Enhanced GaN decomposition in H2 near atmospheric pressures

Cited by 83 publications

References 20 publications

In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction

In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction

MOCVD growth of GaN-based high electron mobility transistor structures

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

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