High reflectivity GaN/Air vertical distributed Bragg reflectors fabricated by wet etching of sacrificial AllnN layers

C. Xiong, P.R. Edwards, G. Christmann, E. Gu, Martin Dawson, J.J. Baumberg, R.W. Martin, I.M. Watson

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Abstract

Microstructures containing GaN/air distributed Bragg reflector (DBR) regions were fabricated by a selective wet etch to remove sacrificial AlInN layers from GaN-AlInN multilayers. The epitaxial multilayers were grown on free-standing GaN substrates, and contained AlInN essentially lattice matched with GaN in order to minimize strain. Two geometries were defined for study by standard lithographic techniques and dry etching: cylindrical pillars and doubly anchored rectangular bridges. Microreflectivity spectra were recorded from the air-gap DBRs, and indicated peak reflectivities exceeding 70% for a typical 3-period microbridge. These values are likely to be limited by the small scale of the features in comparison with the measurement spot. The stopband in this case was centred at 409 nm, and the reflectivity exceeded 90% of the maximum over 73 nm. Simulations of reflectance spectra, including iterations to layer thicknesses, gave insight into the tolerances achievable in processing, in particular indicating bounds on the parasitic removal of GaN layers during wet etching. Air-gap nitride DBRs as described can be further developed in various ways, including adaptation for electrostatic tuning, incorporation into microcavities, and integration with active emitters.
LanguageEnglish
Article number032001
Number of pages5
JournalSemiconductor Science and Technology
Volume25
Issue number3
DOIs
Publication statusPublished - 5 Feb 2010

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Distributed Bragg reflectors
Wet etching
Bragg reflectors
etching
reflectance
air
Multilayers
Air
Dry etching
Microcavities
Nitrides
iteration
nitrides
Electrostatics
emitters
Tuning
tuning
electrostatics
microstructure
Microstructure

Keywords

  • GaN/Air
  • Bragg reflectors
  • wet etching
  • AllnN layers

Cite this

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title = "High reflectivity GaN/Air vertical distributed Bragg reflectors fabricated by wet etching of sacrificial AllnN layers",
abstract = "Microstructures containing GaN/air distributed Bragg reflector (DBR) regions were fabricated by a selective wet etch to remove sacrificial AlInN layers from GaN-AlInN multilayers. The epitaxial multilayers were grown on free-standing GaN substrates, and contained AlInN essentially lattice matched with GaN in order to minimize strain. Two geometries were defined for study by standard lithographic techniques and dry etching: cylindrical pillars and doubly anchored rectangular bridges. Microreflectivity spectra were recorded from the air-gap DBRs, and indicated peak reflectivities exceeding 70{\%} for a typical 3-period microbridge. These values are likely to be limited by the small scale of the features in comparison with the measurement spot. The stopband in this case was centred at 409 nm, and the reflectivity exceeded 90{\%} of the maximum over 73 nm. Simulations of reflectance spectra, including iterations to layer thicknesses, gave insight into the tolerances achievable in processing, in particular indicating bounds on the parasitic removal of GaN layers during wet etching. Air-gap nitride DBRs as described can be further developed in various ways, including adaptation for electrostatic tuning, incorporation into microcavities, and integration with active emitters.",
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AU - Xiong, C.

AU - Edwards, P.R.

AU - Christmann, G.

AU - Gu, E.

AU - Dawson, Martin

AU - Baumberg, J.J.

AU - Martin, R.W.

AU - Watson, I.M.

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