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Quantum Well Lasers. Christopher P. Heagney Jason Yoo. 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. Objectives. “LASER”. L ight - PowerPoint PPT Presentation
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Quantum Well Lasers
Christopher P. Heagney
Jason Yoo
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
• “LASER” • Light
• Amplification by the
• Stimulated
• Emission of
• Radiation
Electron/Photon Interactions
• Absorption• Spontaneous
Emission• Stimulated Emission
Laser Animation
History1958 - 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
ProblemJth(QC) = [e/21][dz/(Npz)][(m+I)/(in-1)] +
[e/(in-1)BG exp(-/(kT))
= 2 + 1 + (21)/’21
21 = (2/42r2)(A21/v)
Probleme = 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
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
Problem
And the answer is….
The Answer:
1