Nanoscale fissure formation in AlxGa1–xN/GaN heterostructures and their influence on Ohmic contact formation

M. D. Smith, D. Thomson, V. Z. Zubialevich, H. Li, G. Naresh-Kumar, C. Trager-Cowan, P. J. Parbrook

Research output: Contribution to journalArticle

Abstract

Nanoscale surface fissures on AlxGa1–xN/GaN (15 nm/1 µm) heterostructures grown by metalorganic vapour phase epitaxy (MOVPE) were imaged using tapping-mode atomic force microscopy (AFM) and electron channelling contrast imaging (ECCI). Fissure formation was linked to threading dislocations, and was only observed in samples cooled under H2 and NH3, developing with increasing barrier layer Al content. No strain relaxation was detected regardless of fissure formation up to barrier layer Al composition fractions of x = 0.37. A reduction of measured channel carrier density was found in fissured samples at low temperature. This instability is attributed to shallow trap formation associated with fissure boundaries. For Ti/Al/Ni/Au Ohmic contact formation to high Al content barrier layers, fissures were found to offer conduction routes to the 2DEG that allow for low resistance contacts, with fissure-free samples requiring additional optimisation of the metal stack and anneal conditions to achieve contact resistivity of order those measured in fissured samples. In addition, the effects of fissures were found to be detrimental to thermal stability of sheet and contact resistance, suggesting that fissure formation compromises the integrity of the 2DEG.
LanguageEnglish
Article number1600353
Number of pages6
JournalPhysica Status Solidi A
Volume214
Issue number1
Early online date25 Oct 2016
DOIs
Publication statusPublished - 31 Jan 2017

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Two dimensional electron gas
Ohmic contacts
Contact resistance
Heterojunctions
electric contacts
Strain relaxation
barrier layers
Metallorganic vapor phase epitaxy
Sheet resistance
Carrier concentration
Atomic force microscopy
Thermodynamic stability
Metals
Imaging techniques
Electrons
Chemical analysis
low resistance
contact resistance
vapor phase epitaxy
integrity

Keywords

  • nanoscale surface fissures
  • electron channelling
  • contrast imaging
  • AlxGa1–xN/GaN

Cite this

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title = "Nanoscale fissure formation in AlxGa1–xN/GaN heterostructures and their influence on Ohmic contact formation",
abstract = "Nanoscale surface fissures on AlxGa1–xN/GaN (15 nm/1 µm) heterostructures grown by metalorganic vapour phase epitaxy (MOVPE) were imaged using tapping-mode atomic force microscopy (AFM) and electron channelling contrast imaging (ECCI). Fissure formation was linked to threading dislocations, and was only observed in samples cooled under H2 and NH3, developing with increasing barrier layer Al content. No strain relaxation was detected regardless of fissure formation up to barrier layer Al composition fractions of x = 0.37. A reduction of measured channel carrier density was found in fissured samples at low temperature. This instability is attributed to shallow trap formation associated with fissure boundaries. For Ti/Al/Ni/Au Ohmic contact formation to high Al content barrier layers, fissures were found to offer conduction routes to the 2DEG that allow for low resistance contacts, with fissure-free samples requiring additional optimisation of the metal stack and anneal conditions to achieve contact resistivity of order those measured in fissured samples. In addition, the effects of fissures were found to be detrimental to thermal stability of sheet and contact resistance, suggesting that fissure formation compromises the integrity of the 2DEG.",
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Nanoscale fissure formation in AlxGa1–xN/GaN heterostructures and their influence on Ohmic contact formation. / Smith, M. D.; Thomson, D.; Zubialevich, V. Z.; Li, H.; Naresh-Kumar, G.; Trager-Cowan, C.; Parbrook, P. J.

In: Physica Status Solidi A, Vol. 214, No. 1, 1600353, 31.01.2017.

Research output: Contribution to journalArticle

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T1 - Nanoscale fissure formation in AlxGa1–xN/GaN heterostructures and their influence on Ohmic contact formation

AU - Smith, M. D.

AU - Thomson, D.

AU - Zubialevich, V. Z.

AU - Li, H.

AU - Naresh-Kumar, G.

AU - Trager-Cowan, C.

AU - Parbrook, P. J.

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N2 - Nanoscale surface fissures on AlxGa1–xN/GaN (15 nm/1 µm) heterostructures grown by metalorganic vapour phase epitaxy (MOVPE) were imaged using tapping-mode atomic force microscopy (AFM) and electron channelling contrast imaging (ECCI). Fissure formation was linked to threading dislocations, and was only observed in samples cooled under H2 and NH3, developing with increasing barrier layer Al content. No strain relaxation was detected regardless of fissure formation up to barrier layer Al composition fractions of x = 0.37. A reduction of measured channel carrier density was found in fissured samples at low temperature. This instability is attributed to shallow trap formation associated with fissure boundaries. For Ti/Al/Ni/Au Ohmic contact formation to high Al content barrier layers, fissures were found to offer conduction routes to the 2DEG that allow for low resistance contacts, with fissure-free samples requiring additional optimisation of the metal stack and anneal conditions to achieve contact resistivity of order those measured in fissured samples. In addition, the effects of fissures were found to be detrimental to thermal stability of sheet and contact resistance, suggesting that fissure formation compromises the integrity of the 2DEG.

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KW - contrast imaging

KW - AlxGa1–xN/GaN

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