Structure of clean and arsenic-covered GaN(0001) surfaces

Vidhya, R.; Lee, C. D.; Feenstra, R. M.; Smith, Arthur R.; Northrup, John E.; Greve, David W.

doi:10.1016/s0022-0248(99)00570-9

Cited by 48 publications

(42 citation statements)

References 26 publications

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“…Figure 5͑c͒ shows the results for As substitutions. Under As-rich conditions, a stable phase is found, which is in agreement with experiment and previous theoretical results, 35 and under As-poor conditions the behavior is similar to the clean GaN ͑0001͒ surface. The As-adlayer configuration has a lower surface energy than that of the Ga adlayer, consistent with the slightly larger cohesive energy of bulk As ͑2.86 eV/ atom͒ compared to that of Ga ͑2.81 eV/ atom͒.…”

Section: Resultssupporting

confidence: 91%

“…4 for the N trimer. This value is somewhat different from the 2.48 Å calculated by Ramachandran et al 35 This may be due to the presence of the nearby fourth As atom affecting the trimer bond strength. The excess electron charge leads to a change in the character of the surface ͑the surface with an As trimer satisfies electron counting but an adlayer with four As atoms does not͒ and their interaction with the As fourth atom causes an increase in the bond distance between the As trimer atoms.…”

Section: Resultscontrasting

confidence: 84%

“…The Al-adlayer structure is stable by 0.07 eV compared to the clean surface, which is one explanation for the poor quality of growth in the first layer in the epitaxy of Al films over clean GaN ͑0001͒ surfaces reported by Liu et al 38 Due to the surfactant behavior of the In and As ͑Ref. 36͒ atoms these adlayer structures are the most stable of all, which is in accordance with the strong 2 ϫ 2 reflection highenergy electron diffraction ͑RHEED͒ pattern 35 of As on GaN surfaces. Figure 3͑b͒ shows the relative formation energy of adlayer surfaces with one or three N atoms on the top of the 2 ϫ 2 GaN ͑0001͒ surface.…”

Section: Resultssupporting

confidence: 66%

“…For the arsenic 3As1N structure, the three As atoms are bonded to form an equilateral triangle with As-As bond of lengths 2.49 Å, in good agreement with similar calculations. 35 In the optimized final surface structure for the cases of the Al, Ga, and In adlayers, the atomic positions of the adlayer atoms are always above the underlying Ga atoms. In the case of the arsenic adlayer three of the arsenic atoms form a trimer with bond lengths of 2.61 Å, similar to the trimer structure shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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First-principles calculations of2×2reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and As atoms

et al. 2005

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Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The ab initio studies presented here employed a pseudopotential-plane-wave method in order to obtain the minimum-energy configurations of various 2 ϫ 2 GaN͑0001͒ surfaces involving N, Al, Ga, In, and As atoms. Comparison of the various possible reconstructions allows predictions to be made regarding the most energetically favorable configurations. Such comparisons depend on the value of the effective chemical potential of each atomic species, which can be related directly to experimental growth conditions. The most stable structure as a function of chemical potentials is determined. Based on these results we have characterized the effect of N in the adlayer surface and the stability dependence with number of substitutions as a function of the model employed and the possible surfactant character of some of the added atoms. Surface phase diagrams as a function of the chemical potential have been calculated to show the phase transition between the different reconstructions.

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Section: Resultssupporting

confidence: 91%

Section: Resultscontrasting

confidence: 84%

Section: Resultssupporting

confidence: 66%

Section: Resultsmentioning

confidence: 99%

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First-principles calculations of2×2reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and As atoms

et al. 2005

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“…[1][2][3][4][5][6][7][8][9][10] As the Ga concentration on the surface increases, the symmetry of the reconstructions changes from 2ϫ2 to 5ϫ5 to 4ϫ6 and finally to the structure that has been termed the pseudo-1ϫ1 structure. 1,6,9 The pseudo-1ϫ1 phase has been obtained experimentally by terminating MBE growth under Ga-rich conditions and is probably very similar to the structure prevailing during Ga-rich growth.…”

mentioning

confidence: 99%

Structure of GaN(0001): The laterally contracted Ga bilayer model

et al. 2000

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We discuss the energetics and structure of a laterally contracted Ga bilayer model for the Ga-rich pseudo-1ϫ1 phase of the GaN͑0001͒ surface. First-principles total energy calculations reveal that a laterally contracted overlayer of Ga atoms bonded to a 1ϫ1 Ga adlayer is energetically favorable in the Ga-rich limit. The calculations also show that the energy of this surface structure is very insensitive to the lateral position of the contracted layer with respect to the underlying Ga layer. The flatness of the energy surface suggests the presence of rapidly moving domain boundaries separating regions of the surface having different registries. Such motion may lead to the 1ϫ1 corrugation pattern seen in scanning tunneling microscopy images.

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GaN HFETs on SiC Substrates Grown by Nitrogen Plasma MBE

Micovic

Moon

Hussain

et al. 2001

phys. stat. sol. (a)

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AlGaN/GaN heterojunction field effect transistors (HFETs) have recently demonstrated powerhandling capabilities exceeding by almost an order of magnitude those of GaAs-pHEMTs. In addition, several groups have reported that low-noise performance of these high power devices almost matches that of the state of the art GaAs-pHEMTs, despite the relative immaturity of GaN HFET technology. A growing demand for GaN HFET parts that has been created by the recent promising performance of GaN HFETs led to the expansion of our research effort to include a smallscale production capability. Device results and run-to-run reproducibility data presented in this paper clearly demonstrate, that plasma assisted MBE is a viable tool for production of GaN HFETs on SiC wafers.Introduction Recent advances of power performance and speed of AlGaN/GaN heterojunction field effect transistors (HFETs) have surpassed the most optimistic predictions that were put forward only five years ago [1,2]. Several groups have recently demonstrated [3, 6-9] that microwave frequency power-handling capabilities of these devices exceed by almost an order of magnitude those of GaAs pHEMTs. The outstanding performance of GaN HFET's is attributed to their excellent current carrying capability and to high value of electric breakdown field in III-V nitride materials. The maximum drain saturation current density of 1.7 A per mm of gate periphery, reported for these devices [3], is almost a factor of 2 higher than the best values reported for microwave transistors fabricated in other material systems. The high value of saturation current is a consequence of high two-dimensional electron-gas (2DEG) sheet carrier density at AlGaN/GaN interface [4] and high electron drift velocity in GaN [5].An additional advantage of GaN HFETs over other microwave power devices is that high quality GaN films can be epitaxially grown on SiC, which is an excellent thermal conductor. The high thermal conductivity of the substrate is crucial for power transistors, as thermal effects ultimately limit their performance. Semi-insulating (SI) SiC is an ideal substrate for microwave power devices, because it conducts heat almost as efficiently as copper. It is no coincidence, that rapid progress in GaN HFET technology was made once large diameter SI SiC wafers became available [6].The GaN HFET is currently being developed for high-power solid-state amplifiers that will be used in a wide range of systems including future generation radar and satellite communication systems. Recent advances in GaN HFET power electronics include: continuous wave (cw) power density exceeding 9 W/mm at 8 GHz [7], cw power density exceeding 6 W/mm at 20 GHz [3], 23 W of cw power at 9 GHz from a single stage power amplifier fabricated by combining four 1 mm periphery devices

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Structure of clean and arsenic-covered GaN(0001) surfaces

Cited by 48 publications

References 26 publications

First-principles calculations of2×2reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and As atoms

First-principles calculations of2×2reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and As atoms

Structure of GaN(0001): The laterally contracted Ga bilayer model

GaN HFETs on SiC Substrates Grown by Nitrogen Plasma MBE

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