Biomedical Engineering Reference
In-Depth Information
Tabl e 3. 1
Simulation parameters for the PL maps and spectra of chirped
QDM bi-layers
QDM
1
QDM
2
cQD
1
sQD
1
cQD
2
sQD
2
Type I—straddled
I
i
1.000
0.094
0.358
0.071
E
i
(eV)
1.048
1.214*
1.085
1.114*
FWHM (meV)
30.6
77.7*
28.3
51.8*
η
i
1.0-1.6
1.1-1.9
1.0-1.6
1.1-1.9
Type II—staggered
I
i
1.000
0.315
0.591
0.044
E
i
(eV)
1.077
1.160*
1.120
1.213*
FWHM (meV)
40.0
53.0*
40.0
49.5*
η
i
1-1.4
1-1.8
1-1.4
1-1.8
Type III—broken-gap
I
i
1.0 1.0 0.7 0.7
E
i
(eV) 1.078 1.121 1.170 1.220*
FWHM (meV) 33.0 42.4 33.0 65.9*
η
i
1.1-2 1.1-2 1.1-2 1.0-2
Twenty-Kelvin peak energy position
E
i
, relative intensity
I
i
, and FWHM of
cQDs and sQDs ensembles of Types I-III chirped QDM bi-layers extracted
from Fig.
3.10
a-c, respectively. The ideality factor
i
varies linearly with
temperature from the lower limit value at 20 K to the upper limit value
at 300 K. Subscripts 1 and 2 represent the lower and upper QDM layers,
respectively.
E
i
's temperature dependency follows Varshni's equation un-
less marked by * where it instead follows the sigmoidal behavior. FWHM
is assumed constant unless marked by * where it follows the anomalous
temperature behavior. The FWHM is related to the standard deviation
of the Gaussian distribution or the broadening parameter
η
through the
relationship: FWHM (meV)
=
1,665.11
×
Γ . Reproduced from [
23
]
Γ
where the overall intensity
I
at energy
E
and temperature
T
is a summation of
constituent intensities from QDM
1
(cQD
1
and sQD
1
) and QDM
2
(cQD
2
and sQD
2
),
hence the summation from
i
1 to 4. Each constituent's luminescence has a low-
temperature intensity
I
i
at a peak energy
E
i
, a broadening parameter
=
Γ
i
and is
quenched by thermal escape to the WL level
E
WL
.
A
is the pre-exponential factor,
k
B
is the Boltzmann's constant and
η
i
is the ideality factor indicating the dominance
of the WL over other NRR channel(s). If the WL is the sole factor responsible for
quenching, then
η
i
=
1. If other NRR channel(s) co-exist and acting in parallel, then
η
i
>
η
i
is from 1, the less significant the WL is as excitons escape
route. The fitting parameters extracted from the measured spectra are summarized
in Table
3.1
.
The simulated line spectra of Types I-III chirps at selected temperatures are
shown underneath the measured spectra in Fig.
3.10
d-f, respectively. A white noise
is added to the simulated data to reflect the actual noise levels in our setup. The
full simulations of Types I-III chirps covering the 20-300 K temperature range
are shown in the PL maps
I
(
E
,
T
)inFig.
3.11
a-c, respectively. The dashed lines
1. The further
