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??????????InGaAsN??????????
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• Reporter ???
• Adviser ??? ??
• Date 2004/01/06

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Outline

• Introduction
• Comparison of InGaAsN, AlGaInAs, and InGaAsP
• Physics of InGaAsN
• Modern research on InGaAsN
• Conclusion

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Introduction

• Long-wavelength (1.3/1.55 ?m) quantum-well lasers
  based upon InGaAsP materials are widely used in
  optical communications applications, but the
  temperature dependence of these lasers remains an
  issue that limits their performance at high
  temperature.
• Thus, in recent years, different material systems
  have been sought to improve the active region
  performance, including AlGaInAs and InGaAsN.

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Comparison of InGaAsN, AlGaInAs,and InGaAsP
InGaAsN AlGaInAs InGaAsP
Characteristic Temperature, T0 (K) 120 90 60
The rate of the gain peak shift (nm/K) 0.33 0.55 0.59
Band offset ratio (?Ec/?Ev) 3.7 2.57 0.67
me / m0 0.08 0.05 0.06
mhh / m0 0.36 0.48 0.49
Material
Property
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Physics of InGaAsN --- Composition GaAs
substrate

• GaN (4.5Å) and GaAs (5.65Å) have very different
  lattice constants, which means that GaAsN layers
  grown on a GaAs substrate should be highly
  strained. By adding indium we can grow InGaAsN
  layer completely lattice matched to GaAs
  substrate. ? VCSEL
• When substituting just 1 N for As in GaAs, the
  band-gap energy decreases from 1.42 to 1.25 eV at
  room temperature, although the GaN band-gap
  energy is much higher 3.43 eV. This is due to
  the coupling of a nitrogen level with the ?
  conduction band.

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Physics of InGaAsN --- Effective mass

• Because the nitrogen states and the electron
  states in the conduction band repulse each other,
  electron effective mass of InGaAsN is about 0.08
  m0 and is about 1.6 times that of AlGaInAs.
• These values of effective masses result in the
  higher transparency carrier density of InGaAsN.
• However, the large electron effective mass
  improves the matching between the density of
  states of the conduction band and that of the
  valence band (?v 1.4?c), so that the
  differential gain (dg/dn) is enhanced. ?
  High-speed modulation

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Modern research on InGaAsN

• Paper1-APL2003
• Improved photoluminescence of
  InGaAsN-(In)GaAsP quantum well by organometallic
  vapor phase epitaxy using growth pause annealing
• Paper2-APL1999
• Ultrafast (GaIn)(NAs)/GaAs vertical-cavity
  surface-emitting laser for the 1.3 ?m wavelength
  regime
• Paper3-EL2000
• Room temperature continuous wave InGaAsN
  quantum well vertical-cavity laser emitting at
  1.3 ?m.

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Paper1-Active region scheme
Sample A
Sample B C
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Photoluminescence spectra of In0.4Ga0.6As0.995N0.0
05 QW with GaAs and GaAs0.85P0.15 direct barriers

• Without employing a growth pause before and after
  the InGaAsN QW, no luminescence intensity was
  measured from structures with direct barriers of
  GaAs0.85P0.15 .

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The luminescence intensity and the peak emission
wavelength of InGaAsN QW with1.62 eV InGaAsP
direct barriers

• The photoluminescence of the InGaAsN QW with
  InGaAsP direct barriers shows the trend of
  increasing luminescence intensity as the pause
  time is increased.

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The FWHM of the optical luminescence spectra for
InGaAsN QW with 1.62 eV InGaAsP direct barriers

• This improvement is also accompanied by a
  reduction in the full width half maximum FWHM.

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Paper2-Scheme of structure

• The 1.3 ?m VCSEL are designed and grown by
  metal-organic vapor-phase epitaxy (MOVPE).
• They use optical excitation with a mode-locked
  Tisapphire laser (0.92 ?m).

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Intensity of the time-integrated emission as a
function of the internal excitation density

• The threshold excitation densities are between
  1.6 and 2.0 kW/cm2 in the center and near the
  edge of the (GaIn)(NAs) sample.
• The threshold value of the (GaIn)(NAs) VCSEL is
  smaller than the threshold of the
  (GaIn)As/Ga(PAs) VCSEL (4.5 kW/cm2).

1.1?Ith
Center 1.6 kW/cm2
0.8?Ith
Edge 2.0 kW/cm2
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The peak delay time and the peak width of the
VCSEL emission after excitation

• The peak delay time after the excitation and the
  full-width at half-maximum (FWHM) of the peak
  decrease with increasing excitation density.
• The fastest dynamics is measured at an internal
  excitation density of 13.4 kW/cm2, with a peak
  delay time of 15.5 ps and a peak width of 10.5 ps.

13.4 kW/cm2
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Paper3-Scheme of structure

• The VCSEL are grown on GaAs substrates using
  molecular beam epitaxy (MBE).
• They use two relatively low-doped n-type mirrors
  to reduce the free carrier absorption.

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Laser characteristics from 4.5?4.5 ?m2 aperture
at 20?

• The threshold current of the InGaAsN VCSEL is
  1.95 mA.

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Lasing spectrum of InGaAsN VCSEL

• The figure shows the single transverse mode
  lasing spectrum at 1294 nm with 28 dB. Singlemode
  output power of 60?W is obtained at 20?.

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Conclusion(1)

• The advantage of InGaAsN
• 1. High characteristic temperature 120K
• 2. Large band offset ratio 3.7
• 3. Lattice-matched substrate GaAs
• 4. Larger differential gain (dg/dn)
• The disadvantage of InGaAsN
• 1. Heavier electron effective mass
• 2. Higher transparency carrier density
• 3. Low output power of InGaAsN VCSEL

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Conclusion(2)

• InGaAsN is found to be advantageous for
  temperature-insensitive, high-speed modulation
  applications at 1.3 ?m. It is especially
  appropriate for VCSELs that require slow redshift
  of gain with respect to the temperature.
• With further improvements in the mirrors, cavity,
  and quantum well design, we can expect that
  appropriate long wavelength performance will be
  achieved.

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Thanks for your attention!!