Quantum Well Lasers

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Quantum Well Lasers

• Christopher P. Heagney
• Jason Yoo

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Objectives

• What exactly is a LASER?
• Three types of electron/photon interactions
• Background information
• Basic Physics of Lasing

• Active Region Quantum Effects
• Quantum Cascade Lasers
• Threshold Current Calculations

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• LASER

• Light
• Amplification
• by the
• Stimulated
• Emission
• of
• Radiation

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Electron/Photon Interactions

• Absorption
• Spontaneous Emission
• Stimulated Emission

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• Laser Animation

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History

• 1958 - Arthur L. Schalow and Charles H. Townes
  invent the laser and publish a paper title
  Infared and Optical Masers
• 1961 - First continuous operation of an optically
  pumped solid state laser
• 1963 - Quantum well laser first suggested by
  H.Kroemer from the U.S. and Kazrinov and Alferov
  from the Soviet Union.
• 1975 - First quantum well laser operation made by
  J.P. Van der Ziel, R, Dingle, R.C Miller, W.
  Wiegmann, and W.A. Nordland, Jr.
• 1977 - R.D. Dupuis, P.D. Dapkus, N. Holonyak
  submitted paper demonstrating first quantum well
  injection laser
• 1994 - Quantum cascade lasers first developed

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Main requirements for Lasing

• Initial Photons
• Population Inversion
• Threshold Current

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Semiconductor Laser
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Interband Lasing Concept
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Intersubband Lasing Concept
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Threshold Gain Concept

• ?gth mode gain required for lasing
• ai internal mode loss

• ?oe(? gth-ai)L ?be(? gth-ai)L I
• gth (?-1)ai (2L)-1 ln (RoRb)-1

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Quantum Cascade Laser
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• Spikes shown are the energy levels that
  correspond to tunneling phenomena.

• Illustrates Transmission Probability as Electron
  Energy increases. Clearly visible are the
  valence and conduction bands as well as a vivid
  drop in transmission through the energy gap.

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• Quantized Electron and Hole States in a quantum
  box.
• kx and ky are in-plave wave vectors

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Problem
Jth(QC) e/?21dz/(Np?z)(?m?I)/(?in?-?1)
e/(?in?-?1)?BG exp(-?/(kT))
? ?2 ?1 (?2?1)/?21 ?21
(?2/4?2?r2)(A21/?v)
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Problem
e electron charge ?21 stimulated emission
cross section dz first active well width Np
number of cascade stages ?z transverse optical
confinement factor ?m mirror loss ?i internal
mode loss ?in injection efficiency into upper
laser level ?1 lifetime of C1 state ?21
total relaxation time between C2 and C1 ?BG
doping sheet density in the Bragg mirror ?
thermal activation energy ?r mode-refractive
index A21 Einsteins coefficient for
spontaneous emission from level E2 to E1
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Problem
Assumptions
dz 4.5 nm Np 25 cascade stages ?z 2.1 x
10-3 ?m 5.6 cm-1 ?i 10 cm-1 ?1 0.6 ps ?2
1.43 ps ?21 1.8 ps ?BG 1.2 x 1011 cm-2 ?r
3.22 Electron Injection Efficency .8
And the answer is.
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The Answer
1