http://dspace.dtu.ac.in:8080/jspui/handle/123456789/13 2026-06-12T10:36:24Z 2026-06-12T10:36:24Z VATSA, AARUSHI DABAS, MEENAKSHI SINGH, MUKHTIYAR (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22821 2026-06-12T04:25:57Z 2026-05-01T00:00:00Z

Title: THE ROLE OF FRÖHLICH AND INTERVALLEY SCATTERING IN THE THERMOELECTRIC TRANSPORT OF 2D PENTAGONAL BI2X (X= Ge, Sn) NETWORKS Authors: VATSA, AARUSHI; DABAS, MEENAKSHI; SINGH, MUKHTIYAR (SUPERVISOR) Abstract: Two-dimensional (2D) penta-materials exhibiting inherently buckled structures and often highly degenerate multivalley electronic structures are promising thermoelectric candidates. However, most current computational investigations on these materials treat charge-carrier scattering using analytical models based on continuum approximations. Here, we elucidate the potential importance of an ab initio mode-resolved approach to carrier transport for these systems by revisiting the thermoelectric performance of recently predicted penta-Bi2X (X=Ge,Sn) monolayers. Under acoustic deformation potential theory, these materials when suitably hole- doped were previously reported to yield extraordinary peak ZT values of 7.0 and 5.8 at 700 K. However, our calculations reveal that charge transport in these monolayers is significantly restricted when long-range Fröhlich and intervalley scattering processes are incorporated. Consequently, the predicted peak ZT for p-type Bi2Ge at 700 K undergoes a substantial correction from 7.0 to 1.0. Conversely, this correction is far less pronounced for p-type Bi2Sn, which maintains a highly competitive peak ZT of 4.4. This relative robustness is attributed to the notably low lattice thermal conductivity on the order of 10-2 W m-1 K-1 reported in the prior study, which allows a concurrent drop in the electronic thermal conductivity to partially compensate for a heavily decreased electrical conductivity. These insights underscore the importance of advanced scattering models for predicting the performance of non-centrosymmetric materials featuring multiple band and valley degeneracies.

2026-05-01T00:00:00Z DEEPAK Kalra, Yogita (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22820 2026-06-12T04:22:35Z 2026-05-01T00:00:00Z

Title: REALIZATION OF SINGLE PHOTON TRANSPORT IN 2D PHOTONIC CRYSTALS Authors: DEEPAK; Kalra, Yogita (SUPERVISOR) Abstract: Periodic dielectric structures offer a powerful means of controlling light at the wavelength scale. In this study, the propagation of single photon wave packets is investigated in a two dimensional hexagonal photonic crystal composed of gallium arsenide (GaAs) rods in air, operating in the near infrared region. By examining the photonic band structure as a function of the normalized rod radius r/a, a complete transverse magnetic (TM) photonic bandgap is identified near r/a = 0.274. A lattice constant of a = 422 nm is selected so that the operating wavelength of 810 nm lies well within this bandgap region. A W1 photonic crystal waveguide is formed by removing a single row of rods from the periodic lattice. The defect channel allows guided modes to propagate within the photonic bandgap region. Finite difference time domain (FDTD) simulations were used to examine the propagation of a Gaussian wave packet through the waveguide. The transmission coefficient was calculated to be approximately T≈0.983, corresponding to an insertion loss of about 0.073 dB. The simulated field profiles indicate that most of the electromagnetic energy remains confined inside the defect channel during propagation, while only small losses occur near the input and output sections. Overall, the study shows that a standard GaAs W1 photonic crystal waveguide can support efficient single photon transport in the near infrared region. This type of structure could be useful for low loss integrated quantum photonic devices.

2026-05-01T00:00:00Z VERMA, SATYAM SINGH, MUKHTIYAR (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22815 2026-06-11T05:55:35Z 2026-05-01T00:00:00Z

Title: A STUDY OF ANOMALOUS HALL AND NERNST EFFECT IN L21 HUESLER ALLOY Authors: VERMA, SATYAM; SINGH, MUKHTIYAR (SUPERVISOR) Abstract: In the application of efficient materials, including spintronics devices, magnetic field sensors, storage devices, and waste heat energy recovery systems, the anomalous transport phenomena play a crucial role. The anomalous transport, including the AHE and ANE are driven by Berry curvature, which is a geometrical property of SOC electronic bands in the magnetic materials. The Present study utilized the ab- initio calculation method to explore the AHE and ANE in the Co₂CrAs and Co₂CrSb types of Co-based Ferromagnetic Heusler alloys, with magnetic moment of 5 μB. The net magnetization oriented along the [001] direction, the major Berry curvature originates from specific electronic states lying at the Fermi energy in the bandstructure under the SOC effect. The overall large Berry curvature further leads to the large AHC and ANC with values 584.38 (-668.99) Scm-1 and -4.71 (-2.68) Am⁻¹K⁻¹, for Co₂CrAs (Co₂CrSb) Heusler alloy. The pronounced anomalous transport responses obtained for Co₂CrAs and Co₂CrSb Heusler alloys suggest that these materials could serve as promising candidates for emerging quantum technologies and thermoelectric applications.

2026-05-01T00:00:00Z KUMAR, KISLAY Chaujar, Rishu (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22810 2026-06-11T05:08:05Z 2026-05-01T00:00:00Z

Title: TCAD-BASED PERFORMANCE ANALYSIS AND OPTIMISATION OF QUADRUPLE-CHANNEL GERMANIUM STEP-FinFETs WITH TRIPLE-MATERIALGATE ENGINEERING Authors: KUMAR, KISLAY; Chaujar, Rishu (SUPERVISOR) Abstract: The aggressive scaling of the semiconductor devices in the sub-30 nm domain requires new architectural and materials solutions to counter the strong short-channel effects (SCEs) while maintaining high drive currents. This dissertation presents a detailed TCAD study on a novel quadruple-channel Germanium step-FinFET with dual-layer SiO2/HfO2 gate dielectric and Triple-Material Gate (TMG) engineering on Silicon-on Insulator (SOI) substrate. The physical rationale behind the design couples the high carrier mobility of Germanium to the volumetric efficiency of a multi-fin structure . The geometric asymmetry of the step-fin profile optimises ON-state drive and OFF state leakage independently . Furthermore, the TMG structure generates a stepped surface potential along the channel, which decouples the source from the drain potential variations and enhances the carrier transit velocity. The proposed device demonstrates a subthreshold swing of 61.54 mV/dec and a Drain Induced Barrier Lowering (DIBL) of 15.65 mV/V at the gate length of 25 nm with the Sentaurus Device simulations with advanced models for quantum confinement, band to-band tunnelling and surface scattering. The multi-fin Germanium channel exhibits a high maximum transconductance of 18.25 mS/µm and an ON/OFF current ratio larger than 107. Systematic evaluation against silicon-based, single-fin, and uniform-gate benchmarks confirms that the integrated optimization of these four elements delivers short-channel and analog performance metrics that substantially exceed those achievable by any single architectural strategy in isolation. The results establish the proposed device as a very promising candidate for next generation low power high frequency analog and digital applications.

2026-05-01T00:00:00Z