656
23 Electricity-to-Light Conversion
500
490
480
470
460
450
440
W
Fig. 23.22 a–c Electroluminescence intensity map of (In,Ga)N LED at different currents as labeled. d Optical image
of the LED chip (top view). e–g Wavelength images (wavelength of spectral emission maximum) for different currents.
Adapted from [1960]
Fig. 23.23 Lifetime for
70% lumen as a function of
solder temperature T s (for
white Diamond Dragon ®
LED) for various driving
currents (0.3, 0.7, 1.4 and
2.0 A, solid lines from right
to left). The dashed line is
for low driving current and
T s = T j . Adapted
from [1964]
high power LEDs (Fig. 23.23). A current problem is the decrease of efficiency with increasing current
density termed droop, probably due to Auger recombination [1962, 1963].
23.3.6 Quantum Dot LEDs
Quantum dots are an interesting active medium for LEDs due to their spectroscopic properties
(Sect. 14.4.4).
Ultranarrow Spectral Emission
A LED based on a single QD exhibits a rather unique spectrum consisting of a single spectral line, at
least at low temperatures [1965], due to exciton recombination as shown in Fig. 23.24. Such device can
deliver single photons on demand and be a photon source for quantum cryptographic communication. At
higher current also biexciton recombination appears. In [1966, 1967] the triggered emission of photon
pairs from cascade-like XX and X recombination in a single dot and their polarization entanglement is
reported. Entanglement is related to degenerate X and XX emission energy [1968] (cmp. Fig. 14.44).
23 Electricity-to-Light Conversion
500
490
480
470
460
450
440
W
Fig. 23.22 a–c Electroluminescence intensity map of (In,Ga)N LED at different currents as labeled. d Optical image
of the LED chip (top view). e–g Wavelength images (wavelength of spectral emission maximum) for different currents.
Adapted from [1960]
Fig. 23.23 Lifetime for
70% lumen as a function of
solder temperature T s (for
white Diamond Dragon ®
LED) for various driving
currents (0.3, 0.7, 1.4 and
2.0 A, solid lines from right
to left). The dashed line is
for low driving current and
T s = T j . Adapted
from [1964]
high power LEDs (Fig. 23.23). A current problem is the decrease of efficiency with increasing current
density termed droop, probably due to Auger recombination [1962, 1963].
23.3.6 Quantum Dot LEDs
Quantum dots are an interesting active medium for LEDs due to their spectroscopic properties
(Sect. 14.4.4).
Ultranarrow Spectral Emission
A LED based on a single QD exhibits a rather unique spectrum consisting of a single spectral line, at
least at low temperatures [1965], due to exciton recombination as shown in Fig. 23.24. Such device can
deliver single photons on demand and be a photon source for quantum cryptographic communication. At
higher current also biexciton recombination appears. In [1966, 1967] the triggered emission of photon
pairs from cascade-like XX and X recombination in a single dot and their polarization entanglement is
reported. Entanglement is related to degenerate X and XX emission energy [1968] (cmp. Fig. 14.44).