Quantum Well Lasers

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					Quantum Well Lasers




 Christopher P. Heagney
        Jason Yoo
                 Objectives
• What exactly is a   • Active Region
  LASER?                Quantum Effects
• Three types of      • Quantum Cascade
  electron/photon       Lasers
  interactions        • Threshold Current
• Background            Calculations
  information
• Basic Physics of
  Lasing
• “LASER”   • Light
            • Amplification
                by the

            • Stimulated
            • Emission
                 of

            • Radiation
   Electron/Photon Interactions
• Absorption
• Spontaneous
  Emission
• Stimulated Emission
Laser Animation
                            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
Main requirements for Lasing

           • Initial Photons
           • Population Inversion
           • Threshold Current
Semiconductor Laser
Interband Lasing Concept
Intersubband Lasing Concept
         Threshold Gain Concept

Гgth ≡ mode gain
   required for lasing

αi ≡ internal mode
    loss




               Гoe(Г gth-αi)L * Гbe(Г gth-αi)L = I

               gth = (Г-1)[αi + (2L)-1 * ln (RoRb)-1]
Quantum Cascade Laser
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.
• Quantized Electron and Hole States
  in a quantum box.
• kx and ky are in-plave wave vectors
                   Problem
Jth(QC) = [e/21][dz/(Npz)][(m+I)/(in-1)] +
          [e/(in-1)BG exp(-/(kT))


                           = 2 + 1 + (21)/’21
                          21 = (2/42r2)(A21/v)
                                     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 = Einstein’s coefficient for spontaneous emission from level E2 to E1
Assumptions
              Problem               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….
The Answer:



    1