Theory of energy transfer interactions between a pair of two level molecules in the molecular
nanojunction including surface plasmon (SP) dressed interaction of plasmonic nanostructure,
replicating metallic leads is presented. Results on the modification of bare dipolar interaction,
known to be responsible for molecular energy transfer processes, in the proximity of metallic
nanosystem are presented. Specifically, the manuscript includes theoretical investigation of
nanosphere (NSP) monomer, nanoshell (NSH) monomer, and coupled nanosphere pair (dimer)
based nanosystems. Closed form analytical expressions for NSP and NSH structures tailored for molecular nanojunction geometry are derived in the theoretical framework of multipole spectral expansion (MSE) method, which is straightforwardly extendible to dimers and multimers. The role of size and dielectric environment on energy transfer is investigated and interpreted. Theory predicts
that the monomer and dimer both enhance the dipolar interaction, yet, dimer geometry is favorable due to its spectral tuning potential originated from plasmon hybridization and true resemblance with typical molecular nanojunctions.
Overcoming the stringent cooling requirement for the operation of most of the infrared (IR) detectors is one of the major
challenges towards capturing their full potential. Split-off (SO) transitions based detector exhibit encouraging results and
gives hope to provide a novel alternative to the conventional IR detectors operating with cryogenic aid. Recently, a
GaAs/AlGaAs SO detector operating up to 330 K in the 3-5 μm spectral region was developed. This paper presents
various design modifications including graded barrier (in place of flat barrier), and double barrier resonant structure (in
place of a single barrier) to improve the performance of these detectors. The graded barrier improves the detector
performance by reducing the space charge buildup due to the trapping of charge carriers at the emitter-barrier interface;
additionally, the model implementation on GaAs/AlGaAs based detectors also suggests that a barrier offset of 20 meV
approximately doubles the responsivity. The implementation of a double barrier resonant structure increases the escape
of holes from the SO to the light/heavy hole (LH/HH) bands by bringing the two bands into resonance and increases the
response by a factor of ~ 85. The results from our ongoing efforts to extend the concept of SO mechanism based IR
detection towards longer wavelength are also presented. This should be possible by exploiting SO absorption in
alternative material systems such as phosphides and nitrides. The successful utilization of SO mechanism can result in
the high operating temperature detectors operating in mid-IR and terahertz (THz) region.
Recently developed high operating temperature (up to 330 K) GaAs/AlGaAs detectors responding in the 3-5 μm
wavelength range and based on split-off (SO) transitions followed by escape by scattering to the light/heavy
hole(LH/HH) band or by direct quantum mixing of the states offer a viable alternative to present day detectors operating
at cryogenic temperatures. This paper presents a theoretical model to predict the response of SO detectors. The model
calculates the dark current and illuminated currents from the photoabsorption, carrier escape, and transport, explaining
the experimental response. Using this model, different strategies to improve the performance of the GaAs based SO
detectors are presented. A graded barrier improves the performance by reducing the space charge build up, and the
double barrier resonant structure by enhanced escape of holes from the SO to the light/heavy hole bands by bringing the
two bands into resonance. A detailed analysis of the effect of detector parameters on responsivity and D* is made. The
change of material system to GaN/AlGaN should extend the response to longer wavelengths (THz) as its zinc blende and
wurtzite crystal structures have SO transition energies of 20meV and 8meV respectively. Experimental measurement of
SO absorption in GaN and potential THz detector designs are discussed.
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