Key Research Areas

Turning a Temperature Difference into Current

A thermoelectric leg makes electricity from a temperature gradient with no moving parts, no working fluid and nothing to service. The group works on all four families at once — inorganic (Bi₂Te₃ co-doped with Sn and Zn, CoSb₃, SrTiO₃, and the wide-bandgap route through GaN and β-Ga₂O₃), organic (PEDOT:PSS, FeCl₃-doped P3HT), hybrid (PEDOT:PSS/Bi₂Te₃ with reduced graphene oxide, PVDF with nickel nanowires), and flexible and printed devices built from them.

Two results anchor the line. Bismuth telluride, the industry standard, gives up above about 150 °C; GaN and β-Ga₂O₃ keep working far beyond it, and the group published the first wide-temperature Seebeck and Hall study of β-Ga₂O₃ single crystals across 80–630 K. On the printable side, adding reduced graphene oxide to a PEDOT:PSS/Bi₂Te₃ film raised the power factor enough to win the RSC Advances Outstanding Student Paper Award for 2024.

Devices That Hold Up at High Field, High Temperature and High Dose

The materials are SiC, GaN, β-Ga₂O₃ and graphene on silicon; the devices are Schottky diodes, AlGaN/GaN HEMTs, photodetectors and heterostructures. What decides whether any of them works is the interface: the metal–semiconductor contact, the barrier it forms, and the states sitting at it.

Chemically passivating a GaN surface with a ruthenium solution raised the Schottky barrier from 0.78 to 0.91 eV and cut reverse leakage by two orders of magnitude — a decade-long line of work, published in Appl. Phys. Lett. in 2014 and again in 2023, and picked up as a Research Review by Compound Semiconductor. The active DRDO CARS project carries it into qualified ohmic and Schottky contact metallurgy on SiC and III–V material for SSPL-DRDO: the contact problem that the India Semiconductor Mission has to solve before domestic power devices become manufacturable.

Native, Irradiated, Implanted — and Measured While They Form

Every device above is limited by defects the crystal came with and defects something put there. The group treats both: native point defects and dislocations from growth, and induced defects from swift heavy ion irradiation, implantation and gamma exposure. The measurement is deep level transient spectroscopy across 80–500 K, with 1/f noise, Hall transport and admittance spectroscopy alongside it.

The distinctive capability is in-situ DLTS under a live beam: the sample sits in the beamline at the IUAC 15UD Pelletron and the trap spectrum is recorded while ions arrive, rather than reconstructed afterwards from a cooled-down sample. Defect formation and annealing kinetics that post-irradiation measurement simply cannot see — because the transient states have already relaxed — are visible directly. Single-defect spectroscopy of this kind is also what the National Quantum Mission needs from wide-bandgap and 2D platforms, where one charge state decides coherence.

Every Measurement Answered by a Calculation

A capacitance transient tells you a trap sits 0.6 eV below the conduction band. It does not tell you which atom is missing. The group pairs each experimental campaign with first-principles and transport modelling, so that a measured level can be assigned to a structure rather than catalogued as a number.

The toolchain is SRIM/TRIM for the stopping and range of the incident ion and the damage profile it leaves; molecular dynamics for the cascade and its relaxation; DFT in Quantum ATK and WIEN2k for formation energies, charge-state transition levels, band structure and the Seebeck coefficient from the Boltzmann transport equation. The GaN thermoelectric work and the Heusler alloy screening were both experiment and calculation from the start, not a calculation bolted on afterwards.

More Than Five Instruments, Built Here, at a Fraction of the Price

Commercial systems for this work cost tens of lakhs each and arrive configured for somebody else's experiment. The group designs and commissions its own: five cryogenic measurement systems so far, all still in routine operation, each built for high precision at low cost and each opened to users beyond the group.

The Seebeck and resistivity system (80–650 K, wire, film and bulk) was published in Review of Scientific Instruments in 2019 and is now used by collaborating national groups. Alongside it: a ZT and thermal conductivity system to 1000 K, the in-situ DLTS setup, a 1/f noise measurement system, a dipstick optical cryostat, and a CVD growth system to 1400 °C commissioned in the Department at Central University of Jammu. A DST-FIST pulsed laser deposition system is being procured and will be open to departmental users.

2D Materials, Carbon Nanotubes, and What Space Asks of Them

Graphene, MoS₂ and multilayer carbon structures behave differently enough from bulk semiconductors that the defect toolkit has to be re-derived for them. Negative oxygen-ion bombardment of CVD graphene moves the Raman disorder ratio, the defect density and the Fermi level together, and the group has mapped that trajectory against fluence. Pt/MoS₂ junctions give a Schottky barrier with a controllable inhomogeneity.

The application that pulls hardest is space. Carbon nanotube and nanomaterial multilayers are the candidate mirror and detector coatings for extreme-ultraviolet and soft X-ray polarimetry, and the ISRO RESPOND project is building prototypes for a future Indian polarimetric mission. The same materials have to survive the same radiation environment the defect work characterises, which is why the two lines share a beamline.