Biomedical Engineering Reference
In-Depth Information
those of cQDs. As sample temperature varies, cQDs emission is found to simply
follow the InAs bulk bandgap variation in accordance with Varshni's equation.
On the contrary, sQDs exhibit a sigmoidal temperature behavior resulting from
carrier redistribution among inhomogeneous QDs. The two qualitatively different
temperature-dependent PL or the bimodal
optical
property results from the intrinsic
bimodal
size
distribution of our lateral QDM ensemble. With this unique property
we proposed and demonstrated a QDM bi-layer structure that exhibits four GS
energies whose spectra can be arranged to overlap in three basic configurations:
straddled, staggered, and broken-gap. A non-optimized, proof-of-principle structure
shows a broadband spectrum with FWHM of 170 meV. The spectra are well
explained by multi-Gaussian functions with carrier redistributions among sQDs
and quenching via thermal escape and recombination via the wetting layer and
non-radiative recombination centers/channels acting in parallel. We introduced an
ideality factor to indicate the dominance of the WL as the quenching channel. Well-
understood optical properties of lateral QDM single- and bi-layers are necessary if
they are to serve as an active material for devices destined for broadband absorption
such as solar cells or for broadband emissions such as superluminescent diodes.
Acknowledgments
AFM data analyses are performed using Gwyddion. This work is supported
by Thailand Research Fund (RSA5580015, DPG5380002); Nanotec; Integrated Innovation Aca-
demic Center (IIAC), Chulalongkorn University Centenary Academic Development Project; and
the Higher Education Research Promotion and National Research University Project of Thailand,
Office of the Higher Education Commission (CU56-EN09).
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