Chapter 23
Electricity-to-Light Conversion
Abstract Light emitting diodes (LEDs) and laser diodes are the focus of this chapter. For LEDs
materials choices, the concepts of internal and external quantum efficiency as well as device design
are treated. Special devices such as white LEDs, quantum dot and organic LEDs are introduced. For
laser diodes the concepts of gain, loss and threshold, various heterostructures for modern device design
and laser emission properties such as mode spectrum, far field, dynamics and tunability are discussed.
Finally special devices such as the hot hole laser, the cascade laser and semiconductor optical amplifiers
are mentioned.
23.1 Radiometric and Photometric Quantities
23.1.1 Radiometric Quantities
The radiometric quantities are derived from the radiant flux (power) e (or usually simply ) that
is the total power (energy per time) emitted by a source, measured in Watts. The radiant intensity I e
is the radiant flux emitted by a point source into a solid angle,
1 measured in Watts per steradian (or
W/sr). The irradiance E e is the radiant flux per area incident on a given plane, measured in W/m
2 .
The radiance L e is the radiant flux per area and solid angle as, e.g., emitted by an extended source,
measured in W/(m
2 sr).
23.1.2 Photometric Quantities
The photometric quantities are related to the visual impression and are derived from the radiometric
quantities by weighting them with the V (λ) curve.
The luminous flux (luminosity or visible brightness) v of a source with the radiant flux (spectral
power distribution) is given by
1 A solid angle is the ratio of the spherical surface area A and the square of the sphere’s radius r , i.e. = A/r 2 .
© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_23
639
Electricity-to-Light Conversion
Abstract Light emitting diodes (LEDs) and laser diodes are the focus of this chapter. For LEDs
materials choices, the concepts of internal and external quantum efficiency as well as device design
are treated. Special devices such as white LEDs, quantum dot and organic LEDs are introduced. For
laser diodes the concepts of gain, loss and threshold, various heterostructures for modern device design
and laser emission properties such as mode spectrum, far field, dynamics and tunability are discussed.
Finally special devices such as the hot hole laser, the cascade laser and semiconductor optical amplifiers
are mentioned.
23.1 Radiometric and Photometric Quantities
23.1.1 Radiometric Quantities
The radiometric quantities are derived from the radiant flux (power) e (or usually simply ) that
is the total power (energy per time) emitted by a source, measured in Watts. The radiant intensity I e
is the radiant flux emitted by a point source into a solid angle,
1 measured in Watts per steradian (or
W/sr). The irradiance E e is the radiant flux per area incident on a given plane, measured in W/m
2 .
The radiance L e is the radiant flux per area and solid angle as, e.g., emitted by an extended source,
measured in W/(m
2 sr).
23.1.2 Photometric Quantities
The photometric quantities are related to the visual impression and are derived from the radiometric
quantities by weighting them with the V (λ) curve.
The luminous flux (luminosity or visible brightness) v of a source with the radiant flux (spectral
power distribution) is given by
1 A solid angle is the ratio of the spherical surface area A and the square of the sphere’s radius r , i.e. = A/r 2 .
© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_23
639