Electron Spectroscopies of InN grown by HPCVD

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Electron Spectroscopies of InN grown by
HPCVD
Rudra P. Bhatta Solid State Physics (Physics -
8510) Fall 2005
Department of Physics and Astronomy Georgia State
University Atlanta, Georgia
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Outline

• Motivation InN and its application
• InN sample grown by HPCVD
• Auger Electron Spectroscopy
• Data Analysis to Determine Composition
• Composition vs. Treatment and Position
• Low energy electron diffraction
• High Resolution Electron Energy Loss
  Spectroscopy
• Surface Structure and Bonding
• Film Polarity
• Summary
• Future work

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Application of InN In rich group III-Nitides

• High-efficient energy conversion system
• solid state lighting (high-efficient
  light emitting diodes)
•   High speed opto-electronics for optical
  communication systems
•  Solid state lasers operating in the blue and
  ultraviolet regions
•  Terahertz device structures (emitters and
  detectors)
•   Nonlinear optical switching elements.
• Spintronic device structures.

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Motivation for studying indium nitride

• Research on indium nitride growth and
  characterizarion has increased tremendously in
  recent years.
• Controversy in the measurement of fundamental
  properties
• such as band gap, lattice constant, and
  effective mass.
• Difficulty of InN growth due to its low
  dissociation temperature
• and the high vapor pressure of nitrogen over
  InN.
• Potential of high pressure chemical vapor
  deposition (HPCVD)
• - stabilizes InN to higher temperature, and
• - allows growth of InN, GaN, and AlN at
  similar conditions.

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HPCVD grown Indium Nitride
Reactor pressure 15 bar Gas flow velocity 41
cm /s AmmoniaTMI ratio 240 Substrate HPCVD
GaN buffer on sapphire (0001)
Flow Direction
HPCVD Growth N. Dietz and coworkers, JVST B 23,
1790 (2005) or phys. stat. sol. latest issue
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Auger Electron Spectroscopy (AES)

• AES is a surface-sensitive spectroscopic
  technique used for elemental analysis of
  surfaces it offers
• High sensitivity (nearly 1 monolayer) for all
  elements
• except H and He.
• Quantitative compositional analysis of the
  surface region.
• A means of monitoring surface cleanliness of
  samples.

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Auger electrons are the secondary ionized
electrons
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Nitrogen and Indium AES peaks (dN/dE)
Nitrogen Si0.54N0.46
Indium Metal
Hand book of Auger Electron Spectroscopy, 2nd
Edition, L.E.Davis et al., Physical Electronics
Division, 1978
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AES Lineshapes for InN and In
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Peak fitting of InN Auger Spectra
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Peak fitting of InN Auger Spectra
Assumed linear background Integrated area under
peaks carbon 220 285 eV nitrogen 358 392
eV indium 392 418 eV oxygen 500 522 eV
O/In calibrated from native oxide of metallic
indium (In2O3) N/In calibrated from highest
nitrogen content InN (assumed 11)
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Atomic Fraction vs. Sample Treatment
Argon Sputtered Region
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Atomic Fraction vs. Sample Treatment
Atomic Hydrogen Cleaning (AHC) 1000 L H2 over
1800 K Tungsten filament with sample at 350
K 1000 L H2 over 1800 K Tungsten filament with
sample at 600 K. 1 L 1x10-6 torr s
McConville and coworkers, Univ. of Warwick Piper
et al., JVST A 23, 617 (2005).
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Atomic Fraction vs. Position
After Atomic Hydrogen Cleaning
Flow Direction
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Schematic of LEED optics operated as RFA
LEED A technique used for the determination of
surface structure

• Sample sits at
• the center of the grids.
• Grid 14 are grounded.
• Grids 2 3 are at
• potential slightly
• less than that of
• electron gun.
• Only elastically
• scattered electrons
• reach to the
• fluorescent screen.

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LEED image of InN

• Spot positions yield information on the size,
  symmetry and rotational alignments of surface
• unit cell with respect to substrate unit cell.
• Distance between the spots gives information
  about the distances
• between the atoms.
• Sharpness of the
• spots gives insight on how well ordered the
  surface atoms are arranged.

E 39.5 eV
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High Resolution Electron Energy Loss Spectroscopy
HREELS Surface Vibrational Spectroscopy
e- E 12.5 eV 60o from normal
e- ? E lt 500 meV (4000 cm-1) specular collection
InN
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HREELS of InN after AHC
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HREELS of InN after AHC
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HREELS of InN after AHC
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HREELS of InN after AHC
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HREELS of InN after AHC
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HREELS of InN after AHC
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HREELS of InN after AHC
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Surface Structure of InN after AHC
H
N-polar surface consists of N atoms bonded to
three In atoms in the second layer and one
dangling bond normal to the surface. Atomic
hydrogen saturates the dangling bonds to
stabilize the surface.
N
In
Growth Direction
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Summary

• Indium nitride sample grown by high pressure
  chemical vapor deposition was investigated by
  AES, LEED, and HREELS.
• The composition of the InN surface was
  determined by integrating areas under peaks in
  N(E) Auger Electron Spectra.
• Sputtering produces nitrogen deficient surface.
• Atomic hydrogen cleaning (AHC) produces a
  contaminant-free, well- ordered c-plane InN
  surface with a 1x1 LEED pattern.
• HREELS of InN after atomic hydrogen (deuterium)
  cleaning shows
• NH (ND) stretch, bend and bounce vibrational
  modes.
• No InH, NH2, or OH vibrational modes are
  observed.
• InN surface is N-terminated and N-polar, i.e.

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Future work

• To study the desorption rate of hydrogen from the
  surface at different temperature by the process
  of HREELS and temperature programmed desorption
  (TPD).
• To study the reaction of ammonia and trimethyl
  indium (TMI) on the indium nitride surface in
  order to understand the surface reaction during
  the growth.

Thank you for your attention.