Research Publications & Academic Portfolio

Semiconductor Materials and Devices | Thin Film Photovoltaics | O-FET Sensor | Halide provskite LEDS | Materials Characterization|Thin films|

Researcher: Sunil Kumar Samji (PhD)
Focus: Next-Gen Solar Cells (CZTS/CIGS), OFET Sensors, and Ferroelectric Materials, Halide Perovskite LEDS Links: Google Scholar Profile | [LinkedIn Profile]

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🔬 Research Summary

My research focuses on the physics of semiconductor defects, thin-film deposition, and device characterization. I specialize in correlating material microstructure (grain boundaries) with macroscopic device performance (efficiency, sensitivity).

This academic background provides the physical foundation for my work in Yield Engineering and Computational Fab Analytics, where I apply algorithms to solve the very defect challenges I studied experimentally.

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📚 Selected Publications by Topic

1. Defect Physics & Photovoltaics (CZTS/CIGS)

Not very time a prisitne single crystalline semiconductor can be good for a solar cell applications - CAFM studies lets you "sniff" the current at the the interior of the grains and grain boundaries and tell you the story

• "How different are CZTS grain boundaries?"

  • Scripta Materialia (2021)
  • Abstract: Some materials in poly-crystaline form show better solar cell performance than their single-crystalline form. This is well established in CdTe and CuInGaSe2. This work reports CAFM studies on the interior of the grains and grain boundariesof CZTS depsoited on sodalime glass substrate and Si substrate to understand explore two competing theories
  • Link to Paper

• "Light induced phase change in Cu2-xZn1.3SnS4 thin films"

  • Applied Physics Letters (2014)
  • Abstract: Cu2ZnSnS4 and its alloy based thin film solar cells have shown better photovoltaic performance under Cu-poor and Zn-rich conditions. However, the effect of Cu-stoichiometry on the coexistence of kesterite (KS), stannite and/or partially disordered kesterite (PD-KS) phases and their influence on photovoltaic performance is not clearly understood. Raman studies were carried out on Cu2xZn1.3SnS4 (x ¼ 0, 0.3, and 0.5) thin films.
  • Link to Paper

• "Do defects get ordered in Cu2ZnSnS4?"

  • Scripta Materialia (2016)
  • Abstract: Formation of ordered defect compounds and anomalous grain boundary physics are unique to Cu chalcogenides CuInX2 (S/Se) and its alloys. X-ray photoelectron spectroscopy (XPS) studies were carried on Cu2-xZn1.3SnS4 (x = 0.0, 0.3, 0.5 and 0.7) to determine the position of valence band edge and explore the formation of ordered vacancy compounds along with absorption studies. Conductive atomic force microscopy (C-AFM) studies were carried out Cu2ZnSnS4 (CZTS) film deposited on Si and sodalime glass substrates to understand grain boundary physics.
  • Link to Paper

2. OFET Sensors

My work on fabricating and characterizing active sensor devices for signal detection.

• "A spectroscopy and microscopy study of Parylene-C OFETs for explosive sensing"
  • IEEE Sensors Journal (2017)
  • Abstract: In this paper, we have explored Parylene-C (PC) as a sensing material for its unique signature and selectivity for explosive sensing. We have used a bi-layer deposition process to fabricate bottom-gate-top-contact organic field effect transistor (OFET) structures. Opening of dangling bonds on subjecting PC to plasma oxidation (POPC) renders these molecules to be employed as a receptor material in sensing vapors of both explosives and non-explosives, such as Trinitrotoulene (TNT), 1,3,5 trinitro-1,3,5-triazacyclohexane(RDX), etc. The change in: 1) the vibrational modes of the molecule by infrared spectroscopy; 2) surface potential of POPC by Kelvin probe force microscopy (KPFM); and 3) electrical characterization by I–V measurements of PC-based OFET on exposing to vapors have been systematically studied.
  • Link to Paper

3. Material Integration & Thin Films

My work on heterogenous integration of complex materials (PZT on Diamond).

• "Integration of perovskite PZT thin films on diamond substrate without buffer layer"

  • Journal of Physics D: Applied Physics (2012)
  • Abstract: Integration of lead zirconate titanate (PZT) thin film on diamond substrate offers a great deal of potential for the application of multifunctional devices under extreme conditions. However, fabrication of perovskite PZT thin films on diamond substrate without a buffer layer has not been realized to date. We report for the first time on the successful deposition of PZT thin film directly on a diamond substrate without any buffer layer using the pulsed-laser deposition technique. The perovskite phase was realized only under specific growth conditions. X-ray diffraction and Raman studies confirmed the perovskite phase. The ferroelectric behaviour of the deposited PZT thin film was confirmed using piezo response microscope phase image and ferroelectric hysteresis loop..
  • Link to Paper

• "Synthesis and characterisation of CuInGaS2 nano-ink for photovoltaic applications"

  • Journal of Experimental Nanoscience(2013)
  • Abstract: Focused on solution-processable semiconductors (Nano-inks) for scalable manufacturing.
  • Link to Paper

• "Characterization of tribo-layer formed during sliding wear of SiC ball against nanocrystalline diamond coatings"

  • Materials characterization(2014)
  • Abstract: Tribo-layer formation and frictional characteristics of the SiC ball were studied with the sliding test against nanocrystalline diamond coating under atmospheric test conditions. Unsteady friction coefficients in the range of 0.04 to 0.1 were observed during the tribo-test. Friction and wear characteristics were found to be influenced by the formation of cohesive tribo-layer (thickness ~ 1.3 μm) in the wear track of nanocrystalline diamond coating. Hardness of the tribo-layer was measured using nanoindentation technique and low hardness of ~ 1.2 GPa was observed. The presence of silicon and oxygen in the tribo-layer was noticed by the energy dispersive spectroscopy mapping and the chemical states of the silicon were analyzed using X-ray photoelectron spectroscopy. Large amount of oxygen content in the tribo-layer indicated tribo-oxidation wear mechanism..
  • Link to Paper

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🛠 Skills & Techniques

• Device Fabrication: PVD (Sputtering), Spin Coating, Thermal Evaporation etc..
• Characterization: XRD, Raman Spectroscopy, SEM, AFM, KPFM (Kelvin Probe Force Microscopy), C-AFM (Conductive Atomic Force Microscopy), XPS.
• Data Analysis: Modeling defect states, Phase identification, I-V/C-V characteristics.

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This repository serves as the "Physical Theory" counterpart to my "Semiconductor Algorithms Portfolio," demonstrating that my coding skills are built on a decade of hands-on device physics experience.