Atmospheric Pressure Molten Salt-Based Growth of Bulk III-N

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Atmospheric Pressure Molten Salt-Based Growth of
Bulk III-Ns

• K.E. Waldrip, T.M. Kerley, F.M. Delnick, D.
  Ingersoll, A.M. West, and J.Y. Tsao
• Sandia National Laboratories, Albuquerque, NM
  87185

Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin
Company,for the United States Department of
Energy under contract DE-AC04-94AL85000.
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Desires/Requirements for Acceptable Bulk Growth
Technique

• Good crystalline quality (? 1x105cm-2)
• High growth rate (mm/hr)
• Low impurity content
• Scalable
• Controllable
• Manufacturable
• Reasonably inexpensive
• Applicable to InN, GaN, and AlN

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GaN, InN Thermodynamics Typically Leads to
Pressure Vessels for Bulk Growth
Gallium Nitride
Indium Nitride
1600C/45,000 atm
1441ºC/67,000 atm
B.Onderka, J. Unland, and R. Schmid-Fetzer, J.
Mater. Res. 17, 2002, p. 3065-3083.
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1/2N2 3e-? N3- The Reactive Intermediate

• T. Goto and Y. Ito, Electrochemical reduction of
  nitrogen in a molten chloride salt
  Electrochimica Acta, Vol. 43, Nos 21-22, pp
  3379-3384 (1998).

• Possible Nitrogen Sources
• N2 gas
• Clean
• Inexpensive
• Knob to turn on growth experiment
• Continuous, controlled supply
• Powder form Li3N, others
• Buildup of excess cations or e.g. deposition of
  molten lithium
• Explore both types

Report of nitride concentration in LiCl in
literature 2.8 mole
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Ga(l) Li3N ? GaN(s) Electrodeposition

• LiCl-KCl at 450C
• Base Pressure 1x10-6 Torr
• Backfilled to atmosphere with N2
• Controlled current
• 127 min synthesis

EDS 5kV excitation
- P.S.
Ni wire
Pt wire
LiCl-KCl
Powder XRD
Li3N
Ga3
N3-
Ga(l)
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Electrodeposition of GaN
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Morphology can be controlled bythe Current
Density
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Demonstration of Electrochemical Reduction of
Nitrogen Gas
LiCl-KCl 450C, Ga Counter Electrode
1/2 N2 3e- ? N3-
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Potential Advantages for Molten Salt-Based Growth

• Moderate Temperatures (450-1000C)
• Atmospheric Pressure
• Scalable
• Access to reactor during experiment
• In quartz in situ monitoring possibilities
• No nitrogen pressure dependence
• Purification of salt (zone refining,
  distillation/drying, electrochemical
  pretreatments)

Possible disadvantage alkali or halide
incorporation into nitride crystal -possible
negative effect on electronic or optical
properties? -possible doping?
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Final Choice of Growth Approach Will Depend Upon
Solubility
Increasing III-N Solubility in Molten Salt
Electrochemical Generation of Precursors
Electrodeposition
Dissolution and Precipitation
N3- species readily available Can GaN be made
this way?
Ideal Solubility Calculation for GaN

• YES!!
• 0.5 mm sized
• crystals formed
• in two hours

• Reaction 1
• In0 ? In3 3e- Li e- ? Li0
• Reaction 2
• 1/2 N2 3e- ? N3- Cl- ? 1/2 Cl2 e-
• Keep concentration just below solubility limit
• Use salt flow to deliver precursors increase
  flow rate to increase growth rate
• Might use one potentiostat or power supply
• If two or more used, could vary V/III ratio

50-100 ppm gt 50-100 µm/hr (under
diffusion-limited regime)
InN boules could be made this wayDepending upon
the conductivity