Our Solid-state Electronics and Photonics (SSEP) research group explores both theoretical and experimental aspects related to design, fabrication and characterization of novel electronic, optoelectronic, photonic and spintronic devices devices and systems. Here is a brief summary of some of the ongoing research projects of the SSEP research group.
The design and implementation of photonic devices have conventionally relied on ordered materials and nanostructures, where imperfections are generally considered undesirable. Disordered photonics, the area of photonic research which investigates the complex behaviour of light in random or disordered media, offers a paradigm shift in how photonic components can be realized. In our research related to the field of disordered photonics, we explore transmission, absorption and reflection of light in disordered medium. In our finite difference time domain based numerical studies, we also investigate exotic phenomena like Anderson localization, and explore whether it is possible to tailor the randomness of a medium to attain specific light output characteristics.
Spin-based electronic and optoelectronic devices- both fall within the scope of our research. My previous research on spintronics involved design, fabrication and experimental characterization of spin-valves, spin-LEDs and spin-LASERs. More recently our research group has been working on the analysis of spin-transfer-torque magnetic random access memory (STT-MRAM) devices, which are considered to be promising candidates for next-generation data storage owing to their non-volatility, fast access times, scalability and low-power consumption. In our recent work on STT-MRAMs, we investigated device-to-device variability of CoFeB/MgO based STT-MRAMs based on experiments and simulations, taking into account the influence of interface quality, temperature variation and device dimensionality.
The smooth functioning of cyber-physical systems largely rely on the operation of wired or wireless communication nodes, sensors, actuators or on-chip computers, many of which operate with only several milliwatts to few tens of micro-watts of power density. Conventionally these devices are operated with batteries or grid-connected adapters, which have both limited lifetime and non-renewable sources of energy supply. Indoor photovoltaics offer a paradigm shift in how these low-power electronic devices can be supplied energy with. Particularly with recent advancements in solid-state indoor lighting systems, the technology of ambient light to electricity generation is being considered as a viable means to fulfill the energy requirement of the ever-expanding network of Internet of Things. In our research on indoor photovoltaics, we explore the prospect of designing energy-efficient indoor-photovoltaic devices and systems with low-cost material systems.
In our recent work on bioinspired photonics, we drew inspiration from morphology of Coscinodiscus species diatom to design bi-layered photonic structures comprised of dielectric-filled nano-holes of varying diameters to enhance and tune absorption characteristics of GaAs-based thin-film photonic devices. The maximum enhancement factor of the bi-layered structure is about 11% higher than the value obtained for its equivalent single-layered counterpart over the near-ultraviolet to visible regime of the spectra. It has been shown that instead of having misaligned pore-centers as in Coscinodiscus species diatoms, a bi-layered structure designed with layers of identical lattice constant offers significant flexibility in terms of design and practical realization of thin-film photonic devices.
With aggressive scaling of the devices to keep up with Moore’s law, we are inevitably entering a regime where the interconnects, rather than the logic devices become the most critical components for designing. Spoof surface plasmon polariton (SSPP) interconnect offers a novel communication system where the unique electromagnetic properties of metasurface are leveraged for high speed data transfer with low energy budget. Unlike conventional interconnects which incur aggravated signal fidelity at elevated frequencies owing to cross-talk, spoof plasmon channel demonstrates quite reverse trends: the cross-talk is suppressed at high frequency end of its band— allowing the possibility of faster data transfer with signal integrity. In our research on SSPP interconnect, we explore the prospect of utilizing SSPP interconnects for high-speed chip-to-chip communication systems.
Exciton-polaritons or polaritons, which are part-light, part-matter hybrid quasiparticles, offer an entirely new physics for realizing semiconductor lasers. These relatively new solid-state devices, which are more commonly known as polariton lasers, can generate coherent light output at two to three thousand times lower input power than that required for an equivalent photon laser. During my PhD studies back in Michigan, I was actively involved in the design, fabrication and experimental characterization of electrically pumped polariton lasers based on GaAs and GaN material systems. At present my research group is exploring theoretical avenues related to exciton-polariton lasers, particularly the role of defects on the performance characteristics of polariton lasers.
