Reproducible reflection high energy electron diffraction signatures for improvement of AlN using <i>in situ</i> growth regime characterization

Burnham, Shawn D.; Namkoong, Gon; Lee, Kyoung-Keun; Doolittle, W. Alan

doi:10.1116/1.2737435

Cited by 38 publications

(22 citation statements)

References 21 publications

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“…21 However, until now the effects of a quantitative shutter modulation technique, such as MME, have only been reported for AlN. [19][20][21][22] Other groups have used shutter modulation while growing GaN to improve intrarun surface uniformity, but the period and duty cycle were not experimentally determined, resulting in a significantly longer period than what was found necessary in the present work, and the effects on Mg-doped GaN were not discussed. 23 GaN surface morphology is similarly improved by the MME growth technique since it exhibits a laterally contracted metal bilayer much like AlN.…”

Section: Introductionmentioning

confidence: 39%

“…31,32 To minimize the adverse effects of mismatch, lowtemperature nitridation and high-temperature AlN buffer layers were grown before growing the GaN films. 33 Nitridation of the sapphire substrates was done at 200°C for 1 h. 34 The AlN buffer layer was grown using the MME growth technique 22 with a substrate temperature of 800°C, an Al cell temperature of 1150°C ͓3.85ϫ 10 −7 Torr, beam equiva-…”

Section: Methodsmentioning

confidence: 99%

“…The metal modulated epitaxy ͑MME͒ growth technique was developed to specifically address reproducibility issues. [19][20][21][22] The MME growth technique is characterized by a group-III ͑metal͒ flux much higher than the group-V source, which would normally lead to droplets. However, the metal shutter is modulated to avoid droplet buildup and therefore build and deplete the metal bilayer on the growth surface, yielding smoother surfaces, larger grain sizes, and better reproducibility.…”

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confidence: 99%

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Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

Burnham¹,

Namkoong²,

Look³

et al. 2008

Journal of Applied Physics

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The metal modulated epitaxy ͑MME͒ growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7 ϫ 10 20 cm −3 , leading to a hole concentration as high as 4.5ϫ 10 18 cm −3 at room temperature, with a mobility of 1. GaN,7 unintentional hydrogen and oxygen doping, 8,9 a significant compensation of Mg acceptors at high dopant concentrations, 1 and a drastic dependence of incorporation upon the growth regime or III-V ratio.10,11 As a consequence, there is a narrow window of growth conditions, which yield electrically active p-type GaN. Furthermore, even low or moderate hole concentrations are often not consistently obtained and are difficult to reproduce due to the Mg incorporation sensitivity to growth conditions. These complications result in large and varied resistances and mobilities in GaN-based devices that rely on p-type layers. If hole carrier concentrations were to be increased, and p-type doping of GaN standardized, these devices could benefit from better performance and better reliability.Despite the complications associated with Mg-doped GaN, current state-of-the-art reports show promising results and give a reference for comparison. Mg incorporation as determined by secondary ion mass spectroscopy ͑SIMS͒ has been reported to be as high as 8 ϫ 10 20 cm −3 for metal organic chemical vapor deposition 12 and 3.5ϫ 10 20 cm −3 for molecular beam epitaxy ͑MBE͒.13 However, above approximately ͑2 -3.5͒ ϫ 10 20 cm −3 , the Mg incorporation begins to decrease with increased Mg flux 13 and inverts Ga-polar films to N-polar. 14 M-plane ͑1010͒ oriented substrates have been used to achieve a hole concentration as high as p = 7.2 ϫ 10 18 cm −3 .15 Electrical characterization for current stateof-the-art films grown on c-plane substrates is shown in Table I. [16][17][18] Reasonably high hole carrier concentrations are in the range of ͑1-3͒ ϫ 10 18 cm −3 . However, hole concentrations have been reported to be as high as 6 ϫ 10 18 cm −3 , 18 although the carrier concentration was metastable and significantly reduced upon heating during measurement. The metal modulated epitaxy ͑MME͒ growth technique was developed to specifically address reproducibility issues. [19][20][21][22] The MME growth technique is characterized by a group-III ͑metal͒ flux much higher than the group-V source, which would normally lead to droplets. However, the metal shutter is modulated to avoid droplet buildup and therefore build and deplete the metal bilayer on the growth surface, yielding smoother surfaces, larger grain sizes, and better repr...

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Section: Introductionmentioning

confidence: 39%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

Burnham¹,

Namkoong²,

Look³

et al. 2008

Journal of Applied Physics

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“…18 cm -3 [1][2][3][4]. This approach, when applied to higher temperatures or in a predominantly droplet rich regime, as indicated by arrow "a" in Figure 1, results in atomically smooth surfaces normally only found when growing in the Ga-droplet regime.…”

Section: Introduction the State-of-the Art Hole Concentration In Gan mentioning

confidence: 94%

“…The Ga fluxes used are sufficiently large that droplets rapidly form when the Ga shutter opens and are subsequently depleted when the Ga shutter closes. Our previous references detail RHEED signatures useful in identifying the proper growth regimes [1][2][3][4], subsequent work has reduced noise and allowed new physical understanding of the kinetics of growth, summarized in Figure 2. RHEED intensity features have been determined to be related to; (a) the exchange of Ga with the N adsorbed layers on shutter opening, (b) the buildup of the mono/bilayer of Ga, (c) the accumulation of Ga droplets, (d) the consumption of droplets after shutter closing, (e) the consumption of the mono/bilayer, and finally the (f) adsorption of a Nitrogen adlayer.…”

Section: Introduction the State-of-the Art Hole Concentration In Gan mentioning

confidence: 99%

Extremely high hole concentrations in c‐plane GaN

Trybus

Doolittle²,

Moseley

et al. 2009

Phys. Status Solidi (c)

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Metal Modulated Epitaxy (S. D. Burnham et al., J. Appl. Phys. 104, 024902 (2008) [1]) is extended to include modulation of both the shutters of Ga and Mg, the Mg being delivered from a Veeco corrosive series valved cracker (S. D. Burnham et al., Mater. Res. Soc. Proc. 798, Y8.11 (2003) [2]). The Ga fluxes used are sufficiently large that droplets rapidly form when the Ga shutter opens and are subsequently depleted when the Ga shutter closes. The result is the ability to limit surface faceting while predominantly growing under average N‐rich growth conditions and thus, possibly reduce N‐vacancy defects. N‐vacancy defects are known to result in compensation. This ability to grow higher quality materials under N‐rich conditions results in very high hole concentrations and low resistivity p‐type materials. Hole concentrations as high as 2×1019 cm–3 have been achieved on c‐plane GaN resulting in resistivities as low as 0.38 ohm‐cm. The dependence on Ga flux, shutter timing, the corresponding RHEED images for each condition is detailed and clearly show minimization of faceting and crystal quality variations as determined by X‐ray diffraction. Quantification of the Mg incorporation and residual impurities such as hydrogen, oxygen, and carbon by SIMS, eliminates co‐doping, while temperature dependent hall measurements show reduced activation energies. X‐ray diffraction data compares crystalline quality with hole concentration. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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