Biomedical Engineering Reference
In-Depth Information
1.25
a
b
sQDs
200 K
1.20
-1 meV/K
1.15
160
1.10
120
100
cQDs
1.05
c
80
90
sQDs
70
77
60
20 K
50
cQDs
cQDs
sQDs
40
30
0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35
0
50
100
150
200
250
Temperature (K)
Energy (eV)
Fig. 3.6
Optical properties of 1.8/25/1.2 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
0.824 eV, respectively. The
dashed lines
in (
c
) are guide to the eye. Reproduced from [
35
] with
permission from Elsevier
scale to aid visual comparison. The agreement between the experimental trend
and the trend calculated based on Varshni's equation is good, except for the small
diversion at low temperatures which can be further improved by the Fan model [
37
].
The sQDs's energy fast red-shift, usually referred to as sigmoidal [
38
], has
been reported by many groups [
32
,
39
-
41
] and is attributed to carrier escape
and redistribution among inhomogeneous QDs. This occur concurrently with an
anomalous FWHM reduction which is indeed observed here and best explained
together.
