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