278
9 Optical Properties
(a)
(b)
(c)
(d)
Fig. 9.22 Modification of the absorption edge of a direct transition by excitonic effects for different spectral (Lorentzian)
broadening (∝ (E 2 + 2 /4) −1 ), a = 0.01E b
X , b = 0.1E b
X , c = E b
X . d is c in linear scale. Dashed lines are
electron–hole plasma absorption according to (9.45)
Fig. 9.23 Theoretical
dependency (lines) for the
the differences of the
C-line and A-line as well as
B-line and A-line exciton
transition energies in GaN
as a function of the c-axis
strain. Symbols are
experimental data from
[866]. Adapted from [540]
broadening parameters are listed in Table 9.5.
7 The optical transitions in polar semiconductors exhibit
stronger coupling to optical phonons. The phonon coupling parameters from different measurements
on GaN are discussed and compared in [870].
7 Such parameter can be directly determined from spectroscopic broadening (as in [868]) or a time-resolved measurement
of the decay of the coherent polarization (four-wave mixing) as in [869]. In the latter, the decay constant of the dephasing
T 2 is related to the decay constant τ of the FWM-signal by T 2 = 2τ for homogeneous broadening. The Fourier transform
of exp −t/(2τ ) is a Lorentzian of the type ∝ ((E − E 0 ) 2 + 2 /4) −1 with = 1/τ being the FWHM.
9 Optical Properties
(a)
(b)
(c)
(d)
Fig. 9.22 Modification of the absorption edge of a direct transition by excitonic effects for different spectral (Lorentzian)
broadening (∝ (E 2 + 2 /4) −1 ), a = 0.01E b
X , b = 0.1E b
X , c = E b
X . d is c in linear scale. Dashed lines are
electron–hole plasma absorption according to (9.45)
Fig. 9.23 Theoretical
dependency (lines) for the
the differences of the
C-line and A-line as well as
B-line and A-line exciton
transition energies in GaN
as a function of the c-axis
strain. Symbols are
experimental data from
[866]. Adapted from [540]
broadening parameters are listed in Table 9.5.
7 The optical transitions in polar semiconductors exhibit
stronger coupling to optical phonons. The phonon coupling parameters from different measurements
on GaN are discussed and compared in [870].
7 Such parameter can be directly determined from spectroscopic broadening (as in [868]) or a time-resolved measurement
of the decay of the coherent polarization (four-wave mixing) as in [869]. In the latter, the decay constant of the dephasing
T 2 is related to the decay constant τ of the FWM-signal by T 2 = 2τ for homogeneous broadening. The Fourier transform
of exp −t/(2τ ) is a Lorentzian of the type ∝ ((E − E 0 ) 2 + 2 /4) −1 with = 1/τ being the FWHM.