376
12 Heterostructures
(a)
E
E V
E C
E e1
E e2
E h1
E h2
E 11 E 22
E g
E g
barr
QW1
QW2
1.5
1.6
1.7
1.8
1.9
*1000
GaAs/AlGaAs
PL-intensity (arbitrary units)
Energy (eV)
AlGaAs
AlGaAs
AlGaAs
GaAs
QW1
QW2
AlGaAs
(b)
(c)
Fig. 12.38 a Schematic energy diagram of a quantum well with confined electron (e1, e2) and hole (h1, h2) states
and recombination between them at energies E 11 and E 22 . b Schematic sample structure with two GaAs/Al x Ga 1−x As
quantum wells with thicknesses 3 nm and 6 nm. c Photoluminescence spectrum (T = 300 K) of the structure from part
(b). A small amount of barrier luminescence appears at 1.88 eV, according to x = 0.37 (cf. Fig. 6.24c)
a many-body effect, multiple electron–hole scattering with electrons at the Fermi edge, leads to an
additional peak, termed Fermi-edge singularity that is discussed in [1201].
Homogeneous Broadening
The temperature dependence of the homogeneous broadening of quantum well luminescence has
been investigated in [1202]. It follows the dependence of the broadening known from bulk material (Sect. 9.7.7) with similar values for the LO broadening parameter. In Fig. 12.39a the reflectance
spectra for different temperatures of a 17 nm GaAs/Al 0.3 Ga 0.7 As QW are shown. The optical phonon
broadening parameter for various well widths is shown in Fig. 12.39b and coincides with the bulk
value.
The homogeneous broadening leads to excitons with in-plane center-of-mass wave-vector K = 0
being allowed to recombine radiatively. This leads to a linear increase of exciton lifetime as demonstrated for GaAs quantum wells up to 50 K in [1200]. In [1203] all exciton wave-vectors within the light
cone are considered, explaining the linear increase of exciton lifetime in (non-polar) ZnO quantum
wells up to room temperature.
12 Heterostructures
(a)
E
E V
E C
E e1
E e2
E h1
E h2
E 11 E 22
E g
E g
barr
QW1
QW2
1.5
1.6
1.7
1.8
1.9
*1000
GaAs/AlGaAs
PL-intensity (arbitrary units)
Energy (eV)
AlGaAs
AlGaAs
AlGaAs
GaAs
QW1
QW2
AlGaAs
(b)
(c)
Fig. 12.38 a Schematic energy diagram of a quantum well with confined electron (e1, e2) and hole (h1, h2) states
and recombination between them at energies E 11 and E 22 . b Schematic sample structure with two GaAs/Al x Ga 1−x As
quantum wells with thicknesses 3 nm and 6 nm. c Photoluminescence spectrum (T = 300 K) of the structure from part
(b). A small amount of barrier luminescence appears at 1.88 eV, according to x = 0.37 (cf. Fig. 6.24c)
a many-body effect, multiple electron–hole scattering with electrons at the Fermi edge, leads to an
additional peak, termed Fermi-edge singularity that is discussed in [1201].
Homogeneous Broadening
The temperature dependence of the homogeneous broadening of quantum well luminescence has
been investigated in [1202]. It follows the dependence of the broadening known from bulk material (Sect. 9.7.7) with similar values for the LO broadening parameter. In Fig. 12.39a the reflectance
spectra for different temperatures of a 17 nm GaAs/Al 0.3 Ga 0.7 As QW are shown. The optical phonon
broadening parameter for various well widths is shown in Fig. 12.39b and coincides with the bulk
value.
The homogeneous broadening leads to excitons with in-plane center-of-mass wave-vector K = 0
being allowed to recombine radiatively. This leads to a linear increase of exciton lifetime as demonstrated for GaAs quantum wells up to 50 K in [1200]. In [1203] all exciton wave-vectors within the light
cone are considered, explaining the linear increase of exciton lifetime in (non-polar) ZnO quantum
wells up to room temperature.