15. Photons in Semiconductors

15. Photons in Semiconductors

15. Photons in Semiconductors

Semiconductor materials Semiconductor materials

) x ( )

L x

( + = ψ ψ

IV

Si GaAs

Semiconductor materials Semiconductor materials

Selected Elemental and Ill-V Binary Semiconductors

Their Bandgap Energies E_g, at T = 300 K, Bandgap Wavelengths λ_g = hc /E_g, Type of Gap (I = Indirect, D = Direct)

UV

Optical fiber communication

D. Generation, Recombination, Internal QE D. Generation, Recombination, Internal QE

Electron-Hole generation Electron-Hole recombination

radiative recombination : photons

nonradiative recombination : lattice vibrations (phonons), Auger process

Internal quantum efficiency

the ratio of the radiative electron-hole recombination rate to the total (radiative and nonradiative) recombination rate (r).

Or, in radiative and nonradiative lifetimes

GaN 20 ns 0.1 ns 0.1 ns 0.005

INTERACTIONS OF PHOTONS WITH ELECTRONS AND HOLES INTERACTIONS OF PHOTONS WITH ELECTRONS AND HOLES

formation of an electron and a hole at some distance from each other but which are nevertheless bound together by their mutual Coulomb interaction.

Absorption coefficient of bulk semiconductors Absorption coefficient of bulk semiconductors

Si GaAs

Conditions for Absorption and Emission Conditions for Absorption and Emission

Absorption (PD)

Spontaneous Emission

(LED)

Induced Emission

(LD)

Spontaneous emission rate and Absorption coefficient Spontaneous emission rate and Absorption coefficient

Spontaneous Emission Spectral Density in Thermal Equilibrium (direct band-band transition)

Absorption Coefficient in Thermal Equilibrium (direct band-band transition)

Refractive index

Refractive index

Quantum confinement structures Quantum confinement structures

Why?