Investigation of optical emission from Carbon dots (CDs)
Inthis work we investigate the emissive properties like intensity, spectrum, bandwidth of CDs. Recently, we showed enhancement in emission by proper choice of substrate enabling carrier transfer within the heterostructures. Optimization of synthesis and purification are important. We are heading towards fabrication of highly emissive thin films for optoelectronic applications.
Energy levels and mechanisms involved in emission from CDs are topics of debate and interest. Measurements like photoluminescence excitation and transient luminescence can shed light.
Electroabsorption measurements on organic semiconductors
We study the effect of space charge in organic semiconductor thin film on EA signal, and the implications on carrier trapping.
Investigation of optical properties on organic semiconductors
Change of optical emission due to substrate patterning and blending composition in composites are being explored.
Variation of PL intensity as a function of polarization angle on the pentacene grown on the crest (triangle) and trough
(square) of the patterned substrate and on reference unpatterned (circle) substrate. (b) Schematic diagram of the sample indicating
measurement positions for anisotropy mapping (c) Spatial mapping of the polarization anisotropy of the PL emission at the positions
indicated in figure (b).
PL emission efficiency variation with the PCBMconcentration (solid dots) at different excitation intensities. Theoretical fit (dashed lines) using the mean field model. (b) Schematic of the processes considered in the mean field model proposed.
Postdoctoral work
I
worked on time-resolved spectroscopy using
pulsed
laser excitations to study carrier dynamics in semiconductor
heterostructures. One
important aspect of this work was the use of a free electron laser
which emits
pulsed, intense and wavelength tunable mid-infrared to far-infrared
radiation.
This allowed the study of low energy intra-band and excitonic
transitions in semiconductor
quantum wells and dots. The work done can be classified into two parts.
Investigation
of intersublevel carrier dynamics in quantum dots
- Performed
time-resolved photoluminescence quenching measurements using two-color
pulsed laser sources and streak camera based detection
- Demonstrated
the presence of long-lived trapped carriers and their influence on
photoluminescence transients
- Studied
the influence of interdot carrier transfer and the carrier lifetimes in
InAs/GaAs quantum dot ensembles
- Observed
negative spin polarization in circularly polarized photoluminescence
quenching measurements
Investigation
of magneto-excitons in semiconductor quantum wells
- Performed
time-resolved photoluminescence quenching measurements in quantum wells
in presence of external magnetic field
- Photoluminescence
quenching induced intersublevel transitions in the quantum wells showed
exciton and cyclotron resonances
- Observed THz induced
intraexcitonic carrier transfer and manipulated the transfer rates
using an external magnetic field
PhD work
My PhD thesis title was “Optical Polarization Anisotropy in Semiconductor Heterostructures” done under supervision of Prof. Sandip Ghosh at Tata Institute of Fundamental Research, Mumbai.
- Developed
a novel Transmittance Anisotropy Spectroscopy technique
- Showed
that anisotropy in A-plane and M-plane GaN and
- Performed
strain dependent electronic band structure calculations based on the
Bir-Pikus Hamiltonian
- From
polarization properties we confirmed the long debated bandgap of
- Our
calculations showed that InGaN films are more suited as lasing medium
compared to AlGaN films
- Performed
polarized photovoltage spectroscopy on InAs/GaAs quantum dots
- Developed
an empirical model for polarization dependent absorption in quantum
dots
- Explained
the anisotropy in the optical response of quantum dots by difference in
the in-plane electron-hole confinement potential along the crystal axes
Anisotropy
arising from electric field
- Performed
electro-reflectance measurements on GaAs/AlGaAs vertical cavity surface
emitting laser structures
- Simulated
the electro-reflectance spectrum for such multilayer structure from
first principles
- Showed that polarization
dependence of the electro-reflectance signal was due to linear
electro-optic effect