L. R. Ram-Mohan Website

Research Experience

Wavefunction Engineering of Quantum Cascade Lasers for mid-IR a nd TeraHertz: Implemented the concept of wavefunction engineering for quantum devices using finite elements. Extended this to phonon-wavefunction engineering for the design of Terahertz Lasers. Successful design of types-I and -II quantum well lasers, and interband quantum cascade lasers. Successful design of inter-subband quantum cascade TeraHertz emitters.
Linear and Nonlinear Optics of Bulk Semiconductors and Nano structures: Stimulated Plasmon Emission in HgCdTe; Dielectric nonlinearities associated with carrier mass modulation in p-type narrow gap materials. The theory of LO-phonon FIR emission laser; theory of the Γ-X laser in GaAs/AlGaAs superlattices. The theory of band structure, optical properties, nonlinear optical susceptibilities, and transport properties of semiconductor superlattices and quantum well heterostructures. Applications to opto-electronic devices. Investigation of optical properties of compositionally asymmetric quantum wells and trilayer superlattices. Theory of multi-band tunneling in quantum semiconductor heterostructures.
Finite Element Applications to Quantum Mechanics and Nanostructures: Pioneered the use of Finite Element Analysis in quantum mechanical problems. Evaluation of high accuracy (double precision) eigenvalues for quantum mechanical systems and self-consistent solutions for coupled mode and nonlinear problems. Calculations of excitonic binding energy in layered heterostructures and in diluted magnetic semiconductor heterostructures using the finite element method. Application of Finite Element and Boundary Element analysis to electromagnetic transmission; electron transport in quantum semiconductor devices and quantum wires.
Theory of Extraordinary Magnetoresistance (EMR): Its simulation and optimization using the finite element method. The modeling led to novel, successful, working designs for the magnetic sensors used in magnetic storage devices such as read-heads, and in automobiles. Recent advances have led to a whole class of EXX phenomena: opto-conductance (EOC), Piezo-conductance (EPC), and Electro-conductance (EEC), all of which show promise of applications as sensors with extraordinarily high sensitivity. We anticipate several patent applications to accrue from this effort.
Aharonov-Bohm Effect and Modeling Ring Electron Waveguides: Theory of the Aharonov-Bohm interference phenomena in quantum semiconductor rings. A finite element based theory was developed for the transmittance through ring waveguides. The method of modal analysis and, alternatively the use of "stealth elements" for the implementation of “outgoing current" boundary conditions were developed.
Spintronics and Dilute Magnetic Semiconductors: Theory of dielectric and magnetic properties of diluted magnetic semiconductors. The evaluation of the binding energy for the bound magnetic polaron in heterostructures. Study of onset of ferromagnetism in DMS III-V materials. Theory of onset of ferromagnetism in III-V semiconductors doped with Mn.
The theory of Surface Plasmons: Surface plasmon-polaritons and their dispersion relations.
Light Scattering from Magneto-Plasmas in Solids: Nonlinear optical techniques for observing excitations in solids. Application of many-body techniques for obtaining theoretical Estimates for light scattering by magneto-acoustic waves via nonlinear four-wave mixing.
Theory of Electromagnetic Attenuation in Normal and Superconducting Metals and the generation of acoustic waves as a coupled channel problem. Diffuse scattering boundary conditions for electrons leading to Muskhelishvili integral equations.
Theory of Ternary Metallic Interdiffusion: Extraction of ternary diffusion coefficients in such diffusion when the diffusion coefficients are functions of concentration; this makes it a nonlinear problem. Predicting the diffusion path in such metallic couples. Developed a new transfer-matrix method for n-component diffusion in metallic couples.

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