Dr. Amita Rawat Profile

Dr. Amita Rawat

SPIE Involvement:

Author

Area of Expertise:

Semiconductor devices , Static random access memory , Structural characterization , Optoelectronics , Material growth , Electrical characterization

Dr. Amita Rawat is an expert in semiconductor device physics and light-matter interaction. She completed her undergraduate in Electrical Engineering from IIT Patna and her Ph.D. in microelectronics from IIT Bombay. She worked at IMEC, Leuven, Belgium, and developed a novel Nanosheet transistor design for high-performance system applications and worked on developing compact models for large-scale circuit design and simulations. Currently, she is working on CMOS-compatible optoelectronic device modeling, simulations, and fabrication.

Proceedings Article | 12 March 2024 Presentation + Paper

On-chip hyperspectral detectors for fluorescence lifetime imaging

Ahasan Ahamed, Amita Rawat, Lisa McPhillips, Laura Marcu, M. Saif Islam

Proceedings Volume 12853, 1285304 (2024) https://doi.org/10.1117/12.3002476

KEYWORDS: Sensors, Fluorescence lifetime imaging, Avalanche photodetectors, External quantum efficiency, Fluorescence, Tissues, Emission wavelengths, Quantum detection, Photonic nanostructures, Fluorescence spectroscopy

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Fluorescence Lifetime Imaging (FLIM) is a powerful technique that measures the decay time of fluorophores present in tissue samples alluding to their constituent molecules. FLIM has gained popularity in biomedical imaging for applications such as detecting cancerous tumors, surgical guidance, etc. However, conventional FLIM systems are limited by a reduced number of spectral bands and long acquisition time. Moreover, the large footprint, complexity, and cost of the instrumentation make it difficult for clinical applications. In this paper, we demonstrate a reconstruction-based hyperspectral detector that can resolve decay time and intensities in broad spectral ranges while providing high sensitivity, high gain, and fast response time. The hyperspectral detector is comprised of an array of efficient, ultrafast avalanche photodetectors integrated with nanophotonic structures. We utilize different nanostructures in the detectors to modulate light-matter interactions in spectral channels. This allows us to computationally reconstruct the spectral profile of the incoming fluorescence spectrum without the need for additional filters or dispersive optics. Also, the nanophotonic structures enhance efficiency (by a factor of 2 to 10 over different wavelengths) while providing fast response time. An innovative detector design has been employed to reduce the breakdown of the avalanche photodetectors to -7.8V while maintaining high gain (~50) across the spectral range. Therefore, enabling low light detection with a high signal-to-noise ratio for FLIM applications. Added spectral channels would provide valuable information about tissue materials, morphology, and disease diagnosis. Such innovative hyperspectral sensors can now be integrated on-chip capable of miniaturizing the FLIM system and making it a commercially viable tool for clinical use. This technology has the potential to revolutionize the current FLIM system with improved detection capabilities opening doors for new horizons.

Proceedings Article | 11 March 2024 Poster + Paper

Direction of arrival sensing enabled by introducing asymmetric surface structures in photodetectors

Amita Rawat, M. Saif Islam

Proceedings Volume 12880, 128800R (2024) https://doi.org/10.1117/12.3003432

KEYWORDS: Absorption, Signal to noise ratio, Photodetectors, Silicon, Light sources and illumination, Simulations, Finite-difference time-domain method, Data communications, Boundary conditions

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Proceedings Article | 11 March 2024 Poster + Paper

High-speed PiN photodiode design space exploration to break the speed-efficiency trade-off

Amita Rawat, M. Saif Islam

Proceedings Volume 12880, 128800Q (2024) https://doi.org/10.1117/12.3003413

KEYWORDS: PIN photodiodes, Capacitance, Picosecond phenomena, Photodiodes, Light sources and illumination, Silicon, Design, Doping

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Ever-evolving imaging and low-to-single photon-count detection applications demand high-speed, efficient, and complementary metal oxide semiconductor (CMOS) compatible photodetectors. Due to the non-overlapping research and development in the CMOS logic and optoelectronic industry, holistic system optimization is lacking. We propose a PiN device design method addressing the speed-efficiency trade-off and enabling an independent optimization of both speed and absorption efficiency. We present a hybrid device structure combining lateral and vertical PiN architectures. We introduce a highly doped buried P⁺− region connecting the top P⁺− contact doping and separating the N⁺-contact doping by a critical width. The top P⁺− and N⁺− contacts are laterally separated by an i-layer for absorption. The use of a lateral i-layer enables a larger volume for efficient photon absorption, and the presence of a highly doped P⁺− region enables an efficient collection of slow-moving holes after the illumination is turned off. The critical i-layer width sandwiched between the buried P⁺− region and the N⁺− contact doping facilitates an efficient conduction path. We optimize the critical width (optimized width = 200 nm) for device capacitance and the admittance to maximize the response time (rise time, fall time, and full-width half maxima). The optimization is performed using ATLAS Silvaco technology computer-aided design software. The optimized device structure possesses 22 GHz 3 dB bandwidth (BW = 0.35/Fall-time) at 850 nm illumination wavelength as against 0.6-10 GHz 3 dB bandwidth range for conventional PiN devices. We also show that reducing the critical width to zero results in impact ionization drive avalanche phenomenon at ∼6 V applied bias, making these devices suitable for low-power and low-photon count detection. With a large absorber width, an optimized critical conduction path, and a low-bias trigger avalanche process, the proposed photodiodes result in high-speed, high-bandwidth, low-photon count detection, essential for state-of-the-art light detection and ranging systems and the single-photon detectors for quantum communications.

Proceedings Article | 9 March 2024 Presentation

Precision photon manipulation in photodetectors for AI-driven ultrafast sensing and imaging

M. Saif Islam, Ahasan Ahamed, Lisa McPhillips, Amita Rawat

Proceedings Volume PC12895, PC128950B (2024) https://doi.org/10.1117/12.3007784

KEYWORDS: Ultrafast imaging, Photodetectors, Light absorption, Biological imaging, Semiconductors, Miniature imaging systems, Imaging spectroscopy, Film thickness, Ultrafast phenomena, Spectroscopy

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Proceedings Article | 8 March 2024 Presentation + Paper

DC linearity and absorption efficiency enhancement by introducing photon-trapping microstructures into avalanche photodetectors

Lisa McPhillips, Amita Rawat, Ahasan Ahamed, M. Saif Islam

Proceedings Volume 12895, 128950G (2024) https://doi.org/10.1117/12.3003649

KEYWORDS: Avalanche photodetectors, Light sources and illumination, Light absorption, Photodiodes, External quantum efficiency, Photonic microstructures, Semiconducting wafers, Doping, Silicon, Quantum devices

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Proceedings Article | 8 March 2024 Presentation + Paper

Scalable photodetector design with sub-picosecond response time

Ahasan Ahamed, Amita Rawat, Lisa McPhillips, Shih-Yuan Wang, M. Saif Islam

Proceedings Volume 12895, 128950H (2024) https://doi.org/10.1117/12.3002441

KEYWORDS: Picosecond phenomena, Photodetectors, Electric fields, Photodiodes, Design, PIN photodiodes, Doping, Silicon, Dopants, Sensors

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Proceedings Article | 5 October 2023 Presentation + Paper

Advancing multi-dimensional vision: AI-driven imaging using unique photodetectors with integrated surface nanostructures

Ahasan Ahamed, Weiwei Wang, Amita Rawat, Lisa McPhillips, Ekaterina Ponizovskaya Devine, Shih-Yuan Wang, Zhi Ding, M. Saif Islam

Proceedings Volume 12651, 1265104 (2023) https://doi.org/10.1117/12.2682104

KEYWORDS: Nanostructures, Photodetectors, Artificial intelligence, External quantum efficiency, Spectrometers, Spatial resolution, Nanostructuring, Laser nanostructuring, Biomedical optics, Temporal resolution

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SPIE Journal Paper | 24 July 2023 Open Access

Achieving higher photoabsorption than group III-V semiconductors in ultrafast thin silicon photodetectors with integrated photon-trapping surface structures

Wayesh Qarony, Ahmed Mayet, Ekaterina Ponizovskaya-Devine, Soroush Ghandiparsi, Cesar Bartolo-Perez, Ahasan Ahamed, Amita Rawat, Hasina Mamtaz, Toshishige Yamada, Shih-Yuan Wang, M. Saif Islam

APN, Vol. 2, Issue 05, 056001, (July 2023) https://doi.org/10.1117/12.10.1117/1.APN.2.5.056001

KEYWORDS: Silicon, Light absorption, Photodetectors, Ultrafast phenomena, Gallium arsenide, Absorption, Quantum efficiency, Group III-V semiconductors, Fabrication, Film thickness

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SPIE Journal Paper | 20 March 2023

Single microhole per pixel for thin Ge-on-Si complementary metal-oxide semiconductor image sensor with enhanced sensitivity up to 1700 nm

Ekaterina Ponizovskaya-Devine, Ahmed S. Mayet, Amita Rawat, Ahasan Ahamed, Shih-Yuan Wang, Aly F. Elrefaie, Toshishige Yamada, M. Saif Islam

JNP, Vol. 17, Issue 01, 016012, (March 2023) https://doi.org/10.1117/12.10.1117/1.JNP.17.016012

KEYWORDS: Germanium, Crosstalk, Tunable filters, Simulations, Optical filters, Image sensors, Silicon, Light absorption, Quantum efficiency, Near infrared

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Proceedings Article | 3 October 2022 Presentation + Paper

Wavelength selective silicon avalanche photodiodes with controlled wide spectral gain by integrating photon-trapping microstructures

Amita Rawat, Ahasan Ahamed, Lisa Mcphillips, Busra Ergul-Yilmaz, Cesar Bartolo-Perez, Shih-Yuan Wang, M. Saif Islam

Proceedings Volume 12200, 1220005 (2022) https://doi.org/10.1117/12.2637146

KEYWORDS: External quantum efficiency, Silicon, Absorption, Avalanche photodetectors, Quantum efficiency, Avalanche photodiodes, Doping, Scanning electron microscopy, Photonic microstructures, Visual communications

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Proceedings Article | 3 October 2022 Presentation + Paper

Near-infrared sensors for high efficiency and high-temperature operation enabled by ultra-thin type-II quantum wells and photon-trapping structures

Amita Rawat, Anthony M. Chiu, Kwong-Kit Choi, Patrick Oduor, Achyut Dutta, M. Saif Islam

Proceedings Volume 12200, 1220008 (2022) https://doi.org/10.1117/12.2637151

KEYWORDS: Absorption, Quantum efficiency, Finite-difference time-domain method, Indium gallium arsenide, Quantum wells, Sensors, Photodetectors, Gallium antimonide, Optical instrument design, Modulation

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