Yohan Yoon

Korea Aerospace University

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Nikolai B. Zhitenev

National Institute of Standards and Technology

Heayoung P. Yoon

University of Utah

Christopher J. Breshike

United States Naval Research Laboratory

Robert Furstenberg

United States Naval Research Laboratory

Christopher A. Kendziora

United States Naval Research Laboratory

Paul M. Haney

Physical Measurement Laboratory

R. Andrew McGill

United States Naval Research Laboratory

Dongheon Ha

Physical Measurement Laboratory

G. A. Rozgonyi

North Carolina State University

Ik Jae Park

Sookmyung Women's University

Cooperative Institutions

National Institute of Standards and Technology

Center for Nanoscale Science and Technology

United States Naval Research Laboratory

University of Utah

Korea Institute of Science and Technology

University of Maryland, College Park

Seoul National University

Physical Measurement Laboratory

Government of the Republic of Korea

Korea University

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Nanoimaging of local photocurrent in hybrid perovskite solar cells via near-field scanning photocurrent microscopy

Dongheon Ha Yohan Yoon Paul M. Haney Nikolai B. Zhitenev Ik Jae Park

Photocurrent generation of methylammonium lead iodide (CH₃NH₃PbI₃) hybrid perovskite solar cells is observed at the nanoscale using near-field scanning photocurrent microscopy (NSPM). We examine how the spatial map of photocurrent at individual grains or grain boundaries is affected either by sample post-annealing temperature or by extended light illumination. For NSPM measurements, we use a tapered fiber with an output opening of 200 nm in the Cr/Au cladded metal coating attached to a tuning fork-based atomic force microscopy (AFM) probe. Increased photocurrent is observed at grain boundaries of perovskite solar cells annealed at moderate temperature (100 °C); however, the opposite spatial pattern (i.e., increased photocurrent generation at grain interiors) is observed in samples annealed at higher temperature (130 °C). Combining NSPM results with other macro-/microscale characterization techniques including electron microscopy, x-ray diffraction, and other electrical property measurements, we suggest that such spatial patterns are caused by material inhomogeneity, dynamics of lead iodide segregation, and defect passivation. Finally, we discuss the degradation mechanism of perovskite solar cells under extended light illumination, which is related to further segregation of lead iodide.

Photocurrent

Passivation

10.1117/12.2320738

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Rapid detection of infrared backscatter for standoff detection of trace explosives

Christopher J. Breshike Christopher A. Kendziora Robert Furstenberg Yohan Yoon Tyler J. Huffman

The use of rapid scanning quantum cascade lasers in the detection of trace amounts of explosive materials is presented. This technique, infrared backscatter imaging spectroscopy (IBIS), utilizes an array of quick tuning infrared quantum cascade lasers (QCLs) to illuminate targets with mid-IR light, 6 – 11 μm in wavelength, to perform measurements in less than one second. The backscattered signal from targets is collected with a liquid nitrogen cooled MCT focal plane array. This information is stored in a hyperspectral image cube which is then run through a detection algorithm which has been trained on synthetic reflectance spectra of analytes of interest. We discuss the experimental parameters used with the QCLs and the focal plane array to generate and collect the infrared backscatter signal. The performance of the fast scanning QCL is presented in detail along with the experimental protocol used to collect high quality data from targets at proximal standoff distance. Camera frames are collected as the laser wavelength is swept and then are binned and assigned discrete wavelength steps. Spectra are extracted from the binned frames on a pixel by pixel basis. When run at full frame imaging, this results in over 16,000 individual spectra.

Quantum cascade laser

Backscatter (email)

Imaging Spectroscopy

SIGNAL (programming language)

10.1117/12.2558485

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Heterogeneous optoelectronic characteristics of Si micropillar arrays fabricated by metal-assisted chemical etching

Scientific Reports (2020)

Qian Yang David Magginetti Seokmin Jeon Yohan Yoon Tony L. Olsen

Abstract Recent progress achieved in metal-assisted chemical etching (MACE) has enabled the production of high-quality micropillar arrays for various optoelectronic applications. Si micropillars produced by MACE often show a porous Si/SiO x shell on crystalline pillar cores introduced by local electrochemical reactions. In this paper, we report the distinct optoelectronic characteristics of the porous Si/SiO x shell correlated to their chemical compositions. Local photoluminescent (PL) images obtained with an immersion oil objective lens in confocal microscopy show a red emission peak (≈ 650 nm) along the perimeter of the pillars that is threefold stronger compared to their center. On the basis of our analysis, we find an unexpected PL increase (≈ 540 nm) at the oil/shell interface. We suggest that both PL enhancements are mainly attributed to the porous structures, a similar behavior observed in previous MACE studies. Surface potential maps simultaneously recorded with topography reveal a significantly high surface potential on the sidewalls of MACE-synthesized pillars (+ 0.5 V), which is restored to the level of planar Si control (− 0.5 V) after removing SiO x in hydrofluoric acid. These distinct optoelectronic characteristics of the Si/SiO x shell can be beneficial for various sensor architectures.

Isotropic etching

Passivation

10.1038/s41598-020-73445-x

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Reduction of speckle noise and mitigation of beam wander in tunable external cavity quantum cascade lasers using rotating diamond/KBr pellet coupled with multimode fiber

Optics Express (2019)

Yohan Yoon Christopher J. Breshike Christopher A. Kendziora Robert Furstenberg R. Andrew McGill

We experimentally demonstrate speckle noise reduction and beam wander mitigation by using a rotating diamond/KBr pellet and a multimode fiber (MMF). As the diamond/KBr diffuser is rotated, the reflected speckle images that are captured by an infrared camera are temporally averaged. We demonstrate 78% speckle noise reduction by averaging 25 frames, which is within 80% of the theoretical contrast reduction. Large beam position fluctuations are also significantly suppressed by adding the MMF. This combination of beam wander mitigation and speckle reduction offers significant benefits for emerging optical technologies that use quantum cascade lasers as illumination sources.

Quantum cascade laser

Speckle noise

Diffuser (optics)

10.1364/oe.27.008011

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Resonant coupling of nano-resonator coatings measured by near-field scanning photocurrent microscopy

Bulletin of the American Physical Society (2018)

Dongheon Ha Yohan Yoon Nikolai B. Zhitenev

Photocurrent

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Effects of Focused-Ion-Beam Processing on Local Electrical Measurements of Inorganic Solar Cells

Microscopy and Microanalysis (2014)

Heayoung P. Yoon Paul M. Haney Joshua Schumacher K. Siebein Yohan Yoon

An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

10.1017/s1431927614004449

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Effect of nickel contamination on high carrier lifetime n-type crystalline silicon

Journal of Applied Physics (2012)

Yohan Yoon Bijaya Paudyal Jin-Woo Kim Young‐Woo Ok Prashant K. Kulshreshtha

The injection-dependent lifetimes of different levels of Ni-contaminated n-type Czochralski (CZ) silicon wafers were investigated using resonant-coupled photoconductance decay (RCPCD) and quasi-steady-state photoconductance technique (QSSPC). The lifetime degradation of the most heavily contaminated samples was caused by Ni silicide precipitates at the surface of the wafers. The impact on lifetime was determined by surface recombination velocities (SRV). SRV values from RCPCD were comparable to those extracted by the QSSPC technique. A direct correlation between minority carrier lifetime and the concentration of electrically active substitutional Ni and Ni silicide precipitate traps measured using deep level transient spectroscopy was established.

Deep-level transient spectroscopy

Carrier lifetime

Degradation

Surface Photovoltage

10.1063/1.3680880

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Citations (7)

Nanoscale imaging of photocurrent generation of perovskite solar cells

Bulletin of the American Physical Society (2018)

Nikolai B. Zhitenev Dongheon Ha Yohan Yoon Ik Jae Park Sangwook Lee

Photocurrent

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Nanoscale imaging of photocurrent enhancement by resonator array photovoltaic coatings

Nanotechnology (2018)

Dongheon Ha Yohan Yoon Nikolai B. Zhitenev

Nanoscale surface patterning commonly used to increase absorption of solar cells can adversely impact the open-circuit voltage due to increased surface area and recombination. Here, we demonstrate absorptivity and photocurrent enhancement using silicon dioxide (SiO2) nanosphere arrays on a gallium arsenide (GaAs) solar cell that do not require direct surface patterning. Due to the combined effects of thin-film interference and whispering gallery-like resonances within nanosphere arrays, there is more than 20% enhancement in both absorptivity and photocurrent. To determine the effect of the resonance coupling between nanospheres, we perform a scanning photocurrent microscopy based on a near-field scanning optical microscopy measurement and find a substantial local photocurrent enhancement. The nanosphere-based antireflection coating (ARC), made by the Meyer rod rolling technique, is a scalable and a room-temperature process; and, can replace the conventional thin-film-based ARCs requiring expensive high-temperature vacuum deposition.

Photocurrent

10.1088/1361-6528/aaab0c

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Stochastic Photoresponse‐Driven Perovskite TRNGs for Secure Encryption Systems

Advanced Science (2025)

Dante Ahn M.B. Lee Woochul Kim Yeon Kyung Lee Jun Young Lee

Abstract True random numbers are essential for ensuring information security and supporting simulations across various industries. With the exponential growth of data driven by advancements in artificial intelligence, robust encryption for communications has become increasingly important. While software‐based deterministic random number algorithms are cost‐effective and easy to use, they are vulnerable to attacks by powerful supercomputers, highlighting the need for more secure alternatives. As portable electronic devices and information‐gathering sensors proliferate, portable true random number generators (TRNGs) are critical for maintaining security. In this work, hybrid material‐based photodetectors composed of anionic polymers and perovskites that maximize stochastic photogeneration for TRNG applications are presented. By integrating perovskite photodetectors with simple electronic circuits, compact, low‐power TRNG devices have been developed that are versatile and resilient to environmental factors. These devices generate 10 000 bits s −1 without resets or delays, achieving significant miniaturization. The generated 10 Mbit random number is validated through US National Institute of Standards and Technology (NIST) testing. Using a 480 000‐bit random sequence, perfect image encryption, ensuring protection against hacking are demonstrated. Additionally, the perovskite TRNG can operate under external light even when embedded in pork skin, realizing its potential as an implantable device for personal security and authentication.

NIST

10.1002/advs.202412139

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