Biomedical Engineering Reference
In-Depth Information
Tabl e 5. 1
The comparison of the experimentally measured and theoretically calculated values of
the DOP is provided for various in-plane TE mode directions. Column 1: the QD system under
study. Column 2: the dimensions of the QD layers in the molecules: B is the base diameter and H
is the height of the QD layers. Column 3-6: the values of the DOP calculated from our model. We
provide two additional directions for the DOP, [100] and [010], for comparison purpose. Column
7-8: the values of the DOP extracted from the published experimental measurements. The values
marked with * are taken from Usman et al. [
35
] and the values marked with † are taken from Inoue
et al. [
9
]
QDM Geometry
Theoretical Calculations
Experiment
(B, H) (nm)
DOP
[
100
]
DOP
[
010
]
DOP
[
110
]
DOP
[
110
]
DOP
[
110
]
DOP
[
110
]
0.7
∗
0.71
∗
SQD
(20, 4.0)
0.999
0.999
0.999
0.999
0.67
†
QDM-2
(20, 4.0)
0.77
0.77
0.833
0.836
0.46
†
QDM-3
(20, 4.0)
0.548
0.46
−
0.244
0.72
0.6
†
,
0.36
∗
0.66
∗
QDM-4
(20, 4.0)
0.38
0.371
−
0.45
0.603
−
−
Here we want to point out that the relative magnitude of the TE
[
110
]
mode does
not reduce as the size of the QDM is increased. Even for the largest system under
study, QDM-4, the TE
[
110
]
mode is much stronger than the TM
[
001
]
mode. That
means if the experimental measurements are performed for DOP
[
110
]
, they should
still show significant anisotropy. This is verified by the PL measurements on the
QDM-4 system as shown in Fig.
5.1
of the Ref. [
4
]. These PL measurements on
QDM-4 system indicate a positive value for the DOP
[
110
]
(TE
[
110
]
>
TM
[
001
]
)anda
negative value for the DOP
[
110
]
(TE
[
110
]
<
TM
[
001
]
).
5.4.5
Comparison with the Experimental PL Data
Tab le
5.1
summarizes the calculated values of the DOP from our model along
different directions and compares it with the recently published experimental PL
measurements. Here we also provide theoretically calculated values of the DOP
along the [100] and [010] directions for comparison purpose because some recent
experimental studies [
6
,
8
,
45
] have chosen these directions for investigation of the
DOP and characterization of the polarization response of the QD systems.
The hole state symmetries shown in Fig.
5.7
show strong alignment in the [110]
direction indicating that symmetries to the [100] and [010] directions will be almost
equivalent. Therefore the values of the DOP are nearly equal for the [100] and
[010] directions as mentioned in Table
5.1
. The PL measurements along these two
directions will not exhibit isotropic polarization even for the QDM-4 system. Similar
results were found in an earlier experimental study by Ridha et al. [
45
]. In their
study of the polarization properties of multi-layer stacks based on TE
mode,
they conclude that such systems cannot provide isotropic polarization and therefore
columnar QDs should be studied for this purpose. However, our results show that
the QDM-4 exhibits isotropic polarization if the TE mode is measured along the
high symmetry [110] axis.
[
010
]
