Electrical and Electronic Engineering - Research Publications

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    Genetic optimization of mid-infrared filters for a machine learning chemical classifier
    Tan, H ; Cadusch, JJ ; Meng, J ; Crozier, KB (Optica Publishing Group, 2022-05-23)
    Miniaturized mid-infrared spectrometers present opportunities for applications that range from health monitoring to agriculture. One approach combines arrays of spectral filters with infrared photodetectors, called filter-array detector-array (FADA) microspectrometers. A paper recently reported a FADA microspectrometer in tandem with machine learning for chemical identification. In that work, a FADA microspectrometer with 20 filters was assembled and tested. The filters were band-pass, or band-stop designs that evenly spanned the microspectrometer’s operating wavelength range. However, given that a machine learning classifier can be trained on an arbitrary filter basis, it is not apparent that evenly spaced filters are optimal. Here, through simulations with noise, we use a genetic algorithm to optimize six bandpass filters to best identify liquid and gaseous chemicals. We report that the classifiers trained with the optimized filter sets outperform those trained with evenly spaced filter sets and those handpicked to target the absorption bands of the chemicals investigated.
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    Spectrally Selective Mid-Wave Infrared Detection Using Fabry-Pérot Cavity Enhanced Black Phosphorus 2D Photodiodes.
    Yan, W ; Shresha, VR ; Jeangros, Q ; Azar, NS ; Balendhran, S ; Ballif, C ; Crozier, K ; Bullock, J (American Chemical Society, 2020-10-27)
    Thin two-dimensional (2D) material absorbers have the potential to reduce volume-dependent thermal noise in infrared detectors. However, any reduction in noise must be balanced against lower absorption from the thin layer, which necessitates advanced optical architectures. Such architectures can be particularly effective for applications that require detection only within a specific narrow wavelength range. This study presents a Fabry-Pérot cavity enhanced bP/MoS2 midwave infrared (MWIR) photodiode. This simple structure enables tunable narrow-band (down to 0.42 μm full width at half-maximum) photodetection in the 2-4 μm range by adjusting the thickness of the Fabry-Pérot cavity resonator. This is achieved while maintaining room-temperature performance metrics comparable to previously reported 2D MWIR detectors. Zero bias specific detectivity and responsivity values of up to 1.7 × 109 cm Hz1/2 W-1 and 0.11 A W-1 at λ = 3.0 μm are measured with a response time of less than 3 ns. These results introduce a promising family of 2D detectors with applications in MWIR spectroscopy.
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    Visible to Short-Wave Infrared Photodetectors Based on ZrGeTe4 van der Waals Materials
    Yan, W ; Johnson, BC ; Balendhran, S ; Cadusch, J ; Yan, D ; Michel, JI ; Wang, S ; Zheng, T ; Crozier, K ; Bullock, J (AMER CHEMICAL SOC, 2021-09-15)
    The self-terminated, layered structure of van der Waals materials introduces fundamental advantages for infrared (IR) optoelectronic devices. These are mainly associated with the potential for low noise while maintaining high internal quantum efficiency when reducing IR absorber thicknesses. In this study, we introduce a new van der Waals material candidate, zirconium germanium telluride (ZrGeTe4), to a growing family of promising IR van der Waals materials. We find the bulk form ZrGeTe4 has an indirect band edge around ∼0.5 eV, in close agreement with previous theoretical predictions. This material is found to be stable up to 140 °C and shows minimal compositional variation even after >30 days storage in humid air. We demonstrate simple proof-of-concept broad spectrum photodetectors with responsivities above 0.1 AW-1 across both the visible and short-wave infrared wavelengths. This corresponds to a specific detectivity of ∼109 cm Hz1/2 W-1 at λ = 1.4 μm at room temperature. These devices show a linear photoresponse vs illumination intensity relationship over ∼4 orders of magnitude, and fast rise/fall times of ∼50 ns, also verified by a 3 dB roll-off frequency of 5.9 MHz. As the first demonstration of photodetection using ZrGeTe4, these characteristics measured on a simple proof-of-concept device show the exciting potential of the ZrGeTe4 for room temperature IR optoelectronic applications.
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    Copper Tetracyanoquinodimethane (CuTCNQ): A Metal-Organic Semiconductor for Room-Temperature Visible to Long-Wave Infrared Photodetection
    Balendhran, S ; Hussain, Z ; Shrestha, VR ; Cadusch, J ; Ye, M ; Azar, NS ; Kim, H ; Ramanathan, R ; Bullock, J ; Javey, A ; Bansal, V ; Crozier, KB (AMER CHEMICAL SOC, 2021-08-09)
    Mid-wave and long-wave infrared (MWIR and LWIR) detection play vital roles in applications that include health care, remote sensing, and thermal imaging. However, detectors in this spectral range often require complex fabrication processes and/or cryogenic cooling and are typically expensive, which motivates the development of simple alternatives. Here, we demonstrate broadband (0.43-10 μm) room-temperature photodetection based on copper tetracyanoquinodimethane (CuTCNQ), a metal-organic semiconductor, synthesized via a facile wet-chemical reaction. The CuTCNQ crystals are simply drop-cast onto interdigitated electrode chips to realize photoconductors. The photoresponse is governed by a combination of interband (0.43-3.35 μm) and midgap (3.35-10 μm) transitions. The devices show response times (∼365 μs) that would be sufficient for many infrared applications (e.g., video rate imaging), with a frequency cutoff point of 1 kHz.
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    Long-Wave Infrared Photodetectors Based on 2D Platinum Diselenide atop Optical Cavity Substrates
    Azar, NS ; Bullock, J ; Shrestha, VR ; Balendhran, S ; Yan, W ; Kim, H ; Javey, A ; Crozier, KB (AMER CHEMICAL SOC, 2021-03-22)
    Long-wave infrared (LWIR) photodetection is of high technological importance, having a wide range of applications that include thermal imaging and spectroscopy. Two-dimensional (2D) noble-transition-metal dichalcogenides, platinum diselenide (PtSe2) in particular, have recently shown great promise for infrared detection. However, previous studies have mainly focused on wavelengths up to the short-wave infrared region. In this work, we demonstrate LWIR photodetectors based on multilayer PtSe2. In addition, we present an optical cavity substrate that enhances the light-matter interaction in 2D materials and thus their photodetection performance in the LWIR spectral region. The PtSe2 photoconductors fabricated on the TiO2/Au optical cavity substrate exhibit responsivities up to 54 mA/W to LWIR illumination at a wavelength of 8.35 μm. Moreover, these devices show a fast photoresponse with a time constant of 54 ns to white light illumination. The findings of this study reveal the potential of multilayer PtSe2 for fast and broadband photodetection from visible to LWIR wavelengths.
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    Mid-Wave Infrared Polarization-Independent Graphene Photoconductor with Integrated Plasmonic Nanoantennas Operating at Room Temperature
    Ye, M ; Gao, Y ; Cadusch, JJ ; Balendhran, S ; Crozier, KB (WILEY-V C H VERLAG GMBH, 2021-01-20)
    Graphene photodetectors operating in the mid-wave infrared (MWIR) face challenges that include the optical absorption of monolayer graphene being intrinsically low and the carrier lifetime in graphene being very short. Previous reports of graphene photoconductors in the MWIR have sought to overcome these challenges using approaches that include the integration of plasmonic nanoantennas and/or engineered electrodes. However, this has led to the photoresponse of these detectors being strongly polarization dependent. Here, a graphene photoconductor is reported that achieves polarization-independent and fast response simultaneously via the integration of plasmonic nanoantennas that are termed Jerusalem-cross antennas (JC-antennas). Compared to previous works, the JC-antennas concentrate the incident light onto graphene more efficiently with enhanced polarization-independent optical absorption. MWIR detection is demonstrated at both room temperature and cryogenic temperatures, with measured responsivity of 14.5 V W−1 (room temperature) and 4400 V W−1 (78 K). Due to the carrier collection by the JC-antennas and gapless band structure of graphene, the detector also shows significant and broadband photoresponse that extends to visible and near-infrared wavelengths. The detector shows fast temporal response with a measured rise time of 3 ns, which would be more than sufficient for many practical applications (e.g., imaging).
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    Plasmonic Mid-Infrared Filter Array-Detector Array Chemical Classifier Based on Machine Learning
    Meng, J ; Cadusch, JJ ; Crozier, KB (AMER CHEMICAL SOC, 2021-02-02)
    Numerous applications exist for chemical detection, ranging from the industrial production of chemicals to pharmaceutical manufacturing, environmental monitoring, and hazardous risk control. For many applications, infrared absorption spectroscopy is the favored technique, due to attributes that include short response time, high specificity, minimal drift, in situ operation, negligible sample disruption, and reliability. The workhorse instrument for infrared absorption is the Fourier transform infrared (FTIR) spectrometer. While such systems are suitable for many purposes, new applications would be enabled by small, lightweight, low power and low cost infrared microspectrometers. Here we perform a detailed study on a microspectrometer chemical classifier comprising an array of plasmonic mid-infrared spectral filters used with a photodetector array, whose outputs are analyzed by a machine learning algorithm. We conduct simulations (including noise), demonstrating the identification of six gas-phase and six liquid-phase chemicals. We study the performance of our method at detecting the concentration of acetylene.
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    VCSELs with On-Facet Metasurfaces for Polarization State Generation and Detection
    Wen, D ; Meng, J ; Cadusch, JJ ; Crozier, KB (WILEY-V C H VERLAG GMBH, 2021-02-22)
    Polarization plays a critical role in optical systems that range from optical communications to imaging, lithography, metrology, and data storage. Thus, in systems that need to generate a certain polarization state, a light source (e.g., laser) is combined with polarization control elements such as polarizers, polarizing beam splitters, and waveplates. Similarly, in systems requiring polarization state detection, such elements are combined with photodetectors. There is currently a trend toward miniaturized optical systems. This motivates the question of how to achieve what may be argued as an ultimate level of miniaturization: a single chip that can both generate light with a prescribed polarization state and detect the polarization state of light impinging upon it. This paper demonstrates this via vertical cavity surface emitting lasers (VCSELs) with on-facet metasurfaces. Two classes of devices are demonstrated. The first class uses high-index dielectric metasurfaces (amorphous silicon nanofins), whereas the second class uses plasmonic metasurfaces (aluminum bilayer gratings). Each can operate as a laser (to generate) and as a photodetector (to detect) circularly or linearly polarized light.
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    Vectorial Holograms with Spatially Continuous Polarization Distributions
    Wen, D ; Cadusch, JJ ; Meng, J ; Crozier, KB (AMER CHEMICAL SOC, 2021-02-05)
    Metasurface-based holography presents opportunities for applications that include optical displays, data storage, and optical encryption. Holograms that control polarization are sometimes referred to as vectorial holograms. Most studies on this topic have concerned devices that display different images when illuminated with different polarization states. Fewer studies have demonstrated holographic images whose polarization varies spatially, i.e., as a function of the position within the image. Here, we experimentally demonstrate a vectorial hologram that produces an image with a spatially continuous distribution of polarization states, for the first time to our knowledge. An unlimited number of polarization states can be achieved within the image. Furthermore, the holographic image and its polarization map (polarization vs position in image) are independent. The same image can be thus encoded with different polarization maps. As far as we know, our approach is conceptually new. We anticipate that it could broaden the application scope of metasurface holography.
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    Light-Matter Interaction Enhancement in Anisotropic 2D Black Phosphorus via Polarization-Tailoring Nano-Optics
    Azar, NS ; Bullock, J ; Balendhran, S ; Kim, H ; Javey, A ; Crozier, KB (AMER CHEMICAL SOC, 2021-03-25)
    Black phosphorus (bP), a two-dimensional (2D) layered material, has shown great potential for infrared (IR) optoelectronics owing to the narrow and direct bandgap it exhibits when in multilayer form. However, its thinness and optical anisotropy lead to weak light absorption, which limits the performance of bP-based photodetectors. In this work, we explore plasmonic nanoantennas, optical cavities, and their hybrids that can be integrated with multilayer bP to enhance its light absorption. This is achieved by near-field light intensity enhancement and polarization conversion. In addition, we demonstrate that these nanostructures can boost the spontaneous emission from bP. Light absorption enhancements of up to 185 and 16 times are obtained for linearly polarized and unpolarized IR light, respectively, in comparison with a commonly used device architecture (bP on SiO2/Si). Moreover, IR light emission enhancements of up to 18 times are achieved. The optical nanostructures presented here can be exploited for enhancing the detectivity of photodetectors and electroluminescence efficiency of light-emitting diodes based on bP and other 2D materials.