Biomedical Engineering Reference
In-Depth Information
a
b
1.25
sQDs
1.20
250 K
1.15
-1 meV/K
200
130
1.10
cQDs
150
1.05
100
c
80
77
sQDs
70
20 K
60
50
cQDs
sQDs
cQDs
40
30
0
50
100
150
200
250
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
Temperature (K)
Energy (eV)
Fig. 3.7
Optical properties of 1.8/25/1.5 QDMs: (
a
) PL spectra at various temperatures, shifted
vertically for clarity; temperature dependencies of (
b
) peak energy positions and (
c
)FWHMof
cQDs- and sQDs-related spectra. The
dashed curves
in (
a
) are double Gaussian functions fit.
The
filled-square
and
open-square
symbols in (
b
)and(
c
) are measured values for cQDs- and
sQDs-related spectra, respectively. The
lower
and
upper dashed lines
in (
b
) are bulk InAs bandgap
temperature variation according to Varshni's equation, shifted along the energy axis by 0.667 and
0.797 eV, respectively. The
dashed lines
in (
c
) are guide to the eye. Reproduced from [
35
] with
permission from Elsevier
The cQD and sQD FWHM variations with temperature of the 1.8/25/1.2 and
1.8/25/1.5 QDMs are shown in Figs.
3.6
cand
3.7
c, respectively. Again, the
variations due to cQDs and sQDs are fundamentally different: the cQDs-related
FWHM are approximately the same and are almost constant (40 and 35 meV for
the 1.8/25/1.2 and 1.8/25/1.5 QDMs, respectively) while the sQDs-related FWHM
decrease towards a minimum at intermediate temperatures before increasing again
at high temperatures. The minimum for 1.8/25/1.2 QDMs occurs at around 75 K
while those for 1.8/25/1.5 QDMs occurs at around 100 K.
