Page 118 - Photonics Essentials an introduction with experiments

Light-Emitting Diodes

112 Photonic Devices

Figure 6.6. The emission spectrum of a heterostructure LED with a peak emission
wavelength near 1600 nm. This diode is a laboratory specimen, and is not commercially
available. The active region is approximately one-half wavelength in thickness, and is
surrounded by wider-band gap window materials. This allows the light to escape with-
out being absorbed. Note that the emission spectrum corresponds more closely to that
predicted by our simple model. Careful control over impurities has limited the longer
wavelength tail. The half width of the emission is 60 eV, which is significantly narrow-
er than that measured for the diodes in Figs. 6.4 and 6.5.

1

probability of radiative recombination
rr
= = (6.8)
1 1 probability for all kinds of recombination
+
rr nr
There is no straightforward way to estimate the radiative recombi-
nation time and the nonradiative recombination times from funda-
mental parameters. In particular, the nonradiative recombination
time usually depends on the density of defects in the material, which
is not related to fundamental materials characteristics.

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