Biomedical Engineering Reference
In-Depth Information
a
T (K)
b
T (K)
116
58
39
29
23
19
116
58
39
29
23
19
0.1
sQDs
200 meV
cQDs
250 meV
0.01
cQDs
325 meV
sQDs
160 meV
E
A
1E-3
A
∗
exp(-
I
=
I
0
/[1+
E
A
/
k
B
T
)]
E
A
1E-4
0.1
0.2
0.3
0.4
0.5
0.6
0.1
0.2
0.3
0.4
0.5
0.6
1/kT (1/meV)
1/kT (1/meV)
Fig. 3.8
Integrated intensities of cQDs- and sQDs-related spectra for (
a
) 1.8/25/1.2 and (
b
)
1.8/25/1.5 QDMs, plotted as a function of temperature
T
and 1/
k
B
T
.The
filled-square
and
open-
square
symbols are measured values for cQDs- and sQDs-related spectra, respectively. The
dashed
lines
are single activation energy fittings with pre-exponential factor
A
10
8
=
3
×
and
E
A
as
indicated. Reproduced from [
35
] with permission from Elsevier
cQDs and 160 meV for sQDs, and in the 1.8/25/1.5 QDMs are 325 meV for cQDs
and 200 meV for sQDs. These values agree with the energetic difference between
the related peak energy and the WL energy. The fits for the 1.8/25/1.5 QDMs are
excellent: the cQD peak at 1.075 eV and the sQD peak at 1.195 eV are lower than
the 1.4-eV WL energy by 325 and 205 meV, respectively. The matches are almost
exact. The fits for the 1.8/25/1.2 QDMs are satisfactory for sQDs only: the cQD
peak at 1.075 eV and the sQD peak at 1.240 eV are lower than the 1.4-eV WL
energy by 325 and 160 meV, respectively. The corresponding best fits values are
250 and 150 meV. It is unclear what causes the large discrepancy in the case of
cQDs but possible causes include the presence of some small percentage of excited-
state excitons (which lowers the effective potential barrier or activation energy)
or defects in or around the nanohole-and-mound template (which introduces NRR
centers/channels).
3.5
Stacked QDMs
The existence of two ground-state energies makes lateral QDMs a promising
candidate as a broadband material for near-infrared (NIR) emissions, especially
if more than one active layer is present. It is typical for quantum wells (QWs)
or QDs active layers employed in superluminescent diodes (SLDs) to be chirped,