p-n GaN/InN Heterostructures for Device Application

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p-n GaN/InN Heterostructures for Device
Application Andrei Osinsky SVT Associates,
Eden Prairie, MN 55344
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• SVT Associates
• M.Z.Kauser, B. Hertog, J. Xie, J. Hwang,
  A.M.Dabiran, P.P. Chow
• p-GaN growth, regrowth.
• device fabrication, characterization,
• energy band diagrams modeling.
• Cornell University W.J. Schaff and Hai Lu
• InN growth, re-growth.
• University of Florida K. W. Baik and S.J.
  Pearton
• ICP etching experiments.
• Acknowledgement

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• Outline
• Energy band diagrams for p-GaN/n-InN and
  n-InN/p-GaN role of polarization charges.
• Fabrication / electrical characterization of
  pn-junctions.
• Comparison of n-AlGaN/GaN and n-InGaN/InN 2D
  structures.
• Effect of graded InGaN layers on p-n junctions
  and 2D structures polarization management.
• Summary.

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n-InN/p-GaN and p-GaN/n-InN Heterostructures.

• Simulation of ideal junction
• Type-I Heterostructures
• Ga, In polarity GaN, InN was assumed
• Spontaneous, PSP Piezoelectric, PPE
  polarizations
• p-GaN, n-InN relaxed.
• p-GaN doping Na-5x1017 1/cm3, EA200meV
• n-InN Nd5x1018-1019 1/cm3, Ed30meV
• Discontinuities 13 interface states due to
  defects were not accounted.

Weaker effect of polarization in InN-GaN system
than in GaN-AlN

• ? polarization charge
• Model suggested by O. Ambacher et al. Also
  nonlinear polarization relationship was used

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Energy Band Alignment for n-InN/p-GaN and
p-GaN/n-InN
Interface charges due to defects can be partially
compensated with the polarization charge.
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Growth and Fabrication of n-InN/p-GaN and
p-GaN/n-InN diodes
MBE (Cornell) InN-bottom 3x1017-1019 1/cm3
InN-top 1019 1/cm3, based on PL
0.4-1.3 µm thick MBE (SVT)
p-GaN-bottom 5-7x1017 1/cm3
µ12-17 Hall.
p-GaN-top ??? (5x10171/cm3,
µ-low )
ICP etch (UF) Cl2 BCl3 MAX Selectivity
InNGaN is 13 SF6 for selectivity control
reduce formation of Cl radicals
0.25x0.25 mm2 device
RIE (SVT)_at_150W Cl2 InN- 80nm/min,
GaN-0.23µm/min selectivity 13
p-GaN mesa InN Metal
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I-V characteristics of n-InN/p-GaN and
p-GaN/n-InN diodes
n-InN(top)/p-GaN
p-GaN(top)/n-InN
V
n-InN

• Access resistance of the bottom layer
  determines series resistance on the I-Vs

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2D electron gas at InN/InGaN comparison with
GaN/AlGaN heterostructure.
Structure Composition of In1-xGaxN Polarization charge (cm-2)
InN/In1-xGaxN (pseudomorphic) x0.2 1.041013
InN/In1-xGaxN (pseudomorphic) x0.3 1.361013
In1-xGaxN/ InN(pseudomorphic) x0.2 -1.581013
In1-xGaxN/ InN(pseudomorphic) x0.3 -2.611013
Nonlinear polarization relationship suggested
by O. Ambacher is used.
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Band Gap Engineering Enhancement of conductance
across p-type InGaN/GaN SLs utilizing graded
p-InGaN layers ,
M. Z. Kauser, A. Osinsky, J.W. Dong, Hertog, A.
M. Dabiran, P.P. Chow. Optimization of p-type
AlGaN/GaN and GaN/InGaN Superlattices Design for
Enhanced Vertical Transport, MRS Proceedings,
Boston 2004 M. Z. Kauser, A. Osinsky, A. M.
Dabiran, S. J. Pearton. Optimization of
Conductivity in p-type GaN/InGaN Graded
Superlattices, JAP, 2005
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Enhancement of conductance across InN/InGaN/InN
sandwich using graded InGaN layers polarization
management
Structure Composition of In1-xGaxN Polarization charge (cm-2)
InN/In1-xGaxN x0.2 1.041013
InN/In1-xGaxN x0.3 1.361013
In1-xGaxN/ InN x0.2 -1.581013
In1-xGaxN/ InN x0.3 -2.611013
-?? distributed polarization charge
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Ga-in InGaN
X
0
200
400
Depth (nm)
InGaN graded
InGaN
InN
InN
In real structures Interface charges due to
defects can be partially compensated with the
polarization charge.
In real structures Defects due to mismatch
distribute over the graded thickness, leading to
lower density at interface, potentially lowering
surface pinning
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Summary

• Fabrication processes for InN/GaN and InN/GaN
  were developed.
• p-n and n-p InN/GaN diodes show quasi- Ohmic IVs
  possibly explained by tunneling
• Band structure simulation for ideal relaxed p-n
  and n-p diodes reveal additional band bending due
  to polarization charge at the interface.
• Interface charge engineering Strong negative
  polarization charge of 2.6x1013 1/cm2 magnitude
  can potentially compensate the possible interface
  band bending associated with charged defects in
  the real junctions.
• Insertion of the InGaN graded layers between
  InGaN and InN results in distribution of
  polarization charge and can be possibly used for
  distribution of the charges associated with
  interface defects, which in case of InN surface
  result in Ef surface pinning.
• Also we used the assumption that the density of
  electrically active defects at the interfaces is
  less than at the InN surface (free or oxidized)
• Polarization management can be used for
  efficient compensation of the possible pinning
  of the energy band at the interfaces and
  surfaces.