About

Sukwon Choi is a professor in the Department of Mechanical Engineering at Penn State University. His research areas include energy systems and thermal/fluid sciences, with specific interests in micro/nanoscale thermal characterization, multi-physics analysis of microelectronics and MEMS, wide bandgap and ultra-wide bandgap semiconductor devices, thermal management of microelectronics, and semiconductor device reliability. His work focuses on understanding and improving thermal boundary conductance, device cooling, and the thermal properties of various materials used in electronic and power devices. Professor Choi has contributed to advancing knowledge in the thermal analysis and design of high-electron-mobility transistors (HEMTs), GaN/SiC interfaces, and other wide bandgap semiconductor devices. His research involves experimental and theoretical approaches to optimize thermal performance, enhance device reliability, and develop innovative cooling solutions for microelectronics. His publications reflect a strong emphasis on thermal transport phenomena, interface conductance, and the development of materials and structures for improved thermal management in electronic systems.

Research topics

• Materials science
• Optoelectronics
• Electrical engineering
• Composite material
• Nanotechnology
• Condensed matter physics
• Engineering
• Thermodynamics
• Engineering physics
• Physics

Selected publications

• Ultra-wide bandgap AlN/AlGaN/AlN-on-SiC HEMT with record-high thermal performance

  IEEE Electron Device Letters · 2026-01-01

  articleSenior author

  Ultrawide bandgap (UWBG) AlGaN electronics are being developed for next-generation power conversion and wireless communication systems. However, these devices are prone to overheating due to the poor thermal conductivity (κ) of AlGaN. In this work, a novel AlN/AlGaN/AlN-on-SiC platform with a thermal performance that exceeds that of today’s GaN-on-SiC HEMTs is demonstrated. The device self-heating behavior was characterized via Raman thermometry and thermal design optimization was performed via 3D thermal modeling. The AlN/AlGaN/AlN-on-SiC high electron mobility transistor (HEMT) exhibits a ~20% lower channel temperature rise compared to today’s GaN-on-SiC HEMTs. This was accomplished by minimizing the thickness of the AlGaN channel and employing a high κ AlN buffer and SiC substrate. Thermal design rules presented in this work will facilitate the full exploitation of the electrical benefits offered by the UWBG semiconductor.

  PublisherDOI

• A ratio-based dual-spot-size time-domain thermoreflectance approach for accurate determination of the in-plane thermal conductivity of AlN thin films and beyond

  International Journal of Heat and Mass Transfer · 2026-04-24

  articleSenior authorCorresponding
  PublisherDOI

• Phonon transport in Al-rich AlxGa1−xN thin films

  Journal of Applied Physics · 2025-08-22 · 1 citations

  articleOpen accessSenior author

  AlxGa1−xN with a high Al composition (x) presents significant potential for advancing next-generation high-power electronic devices. To support the thermal design of AlxGa1−xN-based electronics, the thermal conductivity of AlxGa1−xN thin films was measured as a function of Al composition, temperature, and film thickness using time-domain thermoreflectance and frequency-domain thermoreflectance techniques. The measurement results were interpreted by modeling phonon transport in AlxGa1−xN films using the phonon Boltzmann transport equation. Phonon properties, including frequencies, group velocities, and lifetimes, were calculated using a virtual crystal approximation, with the effects of mass-disorder scattering incorporated via the Tamura model. The measured thermal conductivity of Al0.7Ga0.3N is an order of magnitude lower than those for GaN and AlN, exhibits an increase followed by saturation with temperature, and shows a modest decrease with a reduction in the film thickness. The modeling results agree with the measurement results and reveal that mass-disorder scattering and phonon-boundary scattering are the dominant mechanisms that reduce the thermal conductivity of AlxGa1−xN thin films.

  PublisherOA PDFDOI

• Comparison of the MOCVD growth and properties of wafer-scale transition metal dichalcogenide epitaxial monolayers

  2D Materials · 2025-07-29 · 8 citations

  articleOpen accessCorresponding

  Abstract Epitaxial growth of transition metal dichalcogenides (TMDs) by metalorganic chemical vapor deposition is a promising method for wafer-scale synthesis of monolayer films. This study focuses on a comparison of the epitaxial growth of MoS 2 , WS 2 , and WSe 2 monolayers on 2 inch c-plane sapphire substrates using a cold-wall reactor with metal hexacarbonyl and hydride chalcogen sources. Uniform thermofluidic conditions enabled a comparative analysis of nucleation density, domain size, and lateral growth rate across TMD compounds, shedding light on the impact of TMD chemistry on epitaxial growth. Despite the use of chemically analogous precursors such as Mo(CO) 6 or W(CO) 6 and H 2 S or H 2 Se, significant differences in growth behavior are observed. Comprehensive structural, optical, and transport characterizations provide insights into sulfur versus selenium-based TMDs, advancing the understanding of optimized growth conditions for these emerging materials.

  PublisherDOI

• Epitaxial Growth of Single-Crystalline (0002) Beo Film on (201) Β-Ga2o3 Substrate

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Thermal Characterization and Design of AlN/GaN/AlN HEMTs on Foreign Substrates

  IEEE Electron Device Letters · 2025-03-06 · 13 citations

  articleSenior author

  AlN/GaN/AlN high electron mobility transistors (HEMTs) offer enhanced carrier confinement and higher breakdown voltage than conventional AlGaN/GaN HEMTs. In this work, Raman thermometry was used to characterize the self-heating behavior of a single-finger AlN/GaN/AlN HEMT on 6H-SiC. A 3D finite element analysis model was created to optimize the thermal design of the device structure. Simulation results reveal that the optimal buffer layer thicknesses to minimize the channel temperature rise of AlN/GaN/AlN HEMTs on 6H-SiC and diamond substrates are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 2~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.7~\mu $ </tex-math></inline-formula>m, respectively. Moreover, diamond substrate integration further enhances the thermal performance, achieving a ~45% and ~53% reduction in the device thermal resistance as compared to those of an AlN/GaN/AlN HEMT on 6H-SiC and an AlGaN/GaN HEMT on 4H-SiC, respectively.

  PublisherDOI

• Thermal Optimization of the Buffer Layer Thickness of GaN HEMTs

  IEEE Transactions on Electron Devices · 2025-12-04

  articleSenior author

  This work presents a comprehensive study that systematically optimizes the buffer layer thickness of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) in order to minimize the device thermal resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\textit {R}}_{\text {Th}}$</tex-math> </inline-formula>). Time-domain thermoreflectance (TDTR) and Callaway’s phonon gas model were used to create a temperature-dependent anisotropic thermal conductivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $</tex-math> </inline-formula>) dataset of GaN films for a thickness range of 0.2–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu $</tex-math> </inline-formula>m. Device thermal models that employ the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $</tex-math> </inline-formula> data and the measured thermal boundary resistance (TBR) at the GaN/SiC interface were created and validated using Raman thermometry. The models were used to perform thermal optimization of the GaN buffer thickness. For a TBR of ~3 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{{2}}~\cdot $</tex-math> </inline-formula>K/GW and fully open channel operation, reducing the buffer thickness from 2 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.2~\mu $</tex-math> </inline-formula>m decreases the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\textit {R}}_{\text {Th}}$</tex-math> </inline-formula> of single-, two-, and six-finger HEMTs by 4.9%–5.1%. However, when the TBR exceeds 6 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{{2}} \cdot $</tex-math> </inline-formula>K/GW, thicker buffers are favorable. The operational bias condition also plays a pivotal role. Under a partially pinched-off condition (for a TBR of ~3 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{{2}} \cdot $</tex-math> </inline-formula>K/GW), a thicker buffer (2 versus <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.2~\mu $</tex-math> </inline-formula>m) reduces the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\textit {R}}_{\text {Th}}$</tex-math> </inline-formula> by 26%. In addition, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $</tex-math> </inline-formula> models relying on room-temperature or isotropic values were found to lead to incorrect buffer layer design. These results underscore the importance of incorporating accurate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $</tex-math> </inline-formula> data, TBR, and operational bias conditions into the GaN buffer design to minimize the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\textit {R}}_{\text {Th}}$</tex-math> </inline-formula> of GaN HEMTs.

  PublisherDOI

• Impact of thermal crosstalk on dependent failure rates of multilayer ceramic capacitors undergoing lifetime testing

  Journal of Applied Physics · 2025-01-15 · 2 citations

  articleOpen access

  Several research studies have investigated the degradation of BaTiO3-based dielectric capacitor materials, focusing on the impact of composition, defect chemistry, and microstructural design to limit the electromigration of oxygen vacancies under electric fields at finite temperatures. Electromigration can be a dominant mechanism that controls failure rates in the individual multilayer ceramic capacitor (MLCC) components in testing the reliability of failures with highly accelerated lifetime testing (HALT) to determine the mean time to failure of MLCCs surface mounted onto printed circuit boards (PCBs). Conventional assumptions often consider these failures as independent, with no interaction between components on the PCB. However, this study employs a Physics of Failure (PoF) approach to closely examine transient degradation and its impact on MLCC reliability, emphasizing thermal crosstalk and its influence on dependent and independent failure rates. Finite element analysis thermal modeling and infrared thermography were used to assess the impact of circuit layout and component spacing on heat dissipation and thermal crosstalk under various electrical stress conditions. The study distinguishes between dependent and independent failures under a HALT, quantified through a β′ factor reflecting common cause failures due to thermal crosstalk. Through a series of experimental and statistical analyses, the β′ factor is evaluated with respect to temperature, voltage, and component spacing. These insights highlight the importance of understanding the nature of the data in reliability testing of MLCCs and optimizing the layout design of high-density circuits to mitigate dependent failures, improving overall reliability and informing better design and packaging strategies.

  PublisherOA PDFDOI

• Inter-Laboratory Comparison of Gate Resistance Thermometry Measurements of RF GaN HEMTs

  2025-10-12

  article

  This paper reports an inter-laboratory comparison of the thermal characterization of GaN HEMTs using the gate resistance thermometry (GRT) technique. GRT test benches at three different universities in the United States are utilized to conduct GRT calibration and biased transistor measurements using best practices at each respective laboratory. The results in this work demonstrate excellent precision of GRT calibration and measurements - a critical assessment for ensuring accurate electrothermal modeling of GaN HEMTs. This work could be useful for GaN HEMT characterization and modeling engineers for determining the level of precision in GRT measurements and understanding discrepancies between GRT measurements collected at different laboratories.

  PublisherDOI

• Characterization of hotspot formation in AlGaN/GaN HEMTs by probing Raman scattering through an optically transparent gate

  Journal of Applied Physics · 2025-07-01 · 1 citations

  articleOpen accessSenior author

  AlGaN/GaN high electron mobility transistors (HEMTs) are in high demand for wireless communication and power conversion applications due to their high-power and high-frequency capabilities. However, the extremely high operational heat flux often leads to the formation of hotspots that negatively impact the device performance and reliability. In this work, an AlGaN/GaN HEMT with a transparent indium tin oxide (ITO) gate was fabricated to enable in situ characterization of the channel peak temperature that occurs underneath the gate electrode. Raman thermometry was performed to measure the temperature of the GaN layer under various bias conditions while power dissipation was kept constant. An electro-thermal device model was created to validate experimental results, to explain the physical origins of the bias-dependent self-heating behavior, and to calculate the peak temperature of the two-dimensional electron gas channel. Experimental results show that the temperature measured next to the drain side edge of the gate (which is a normal practice when characterizing a standard metal-gated device) resulted in a 32% lower value than the temperature underneath the drain end of the gate acquired from the ITO-gated device. This underestimation of temperature could result in overestimation of the component lifetime during accelerated operational life tests.

  PublisherDOI

Recent grants

• FuSe-TG: Electro-Thermal Co-Design Center for Ultra-Wide Bandgap Semiconductor Devices

  NSF · $450k · 2023–2025

• GOALI: An Experimental Study of Electric Field Driven Non-Fourier Thermal Transport in High Power Electronic Devices

  NSF · $350k · 2020–2023

Frequent coauthors

• Samuel Graham

  University of Maryland, College Park

  73 shared

• Bikramjit Chatterjee

  Lawrence Livermore National Laboratory

  56 shared

• Eric R. Heller

  United States Air Force Research Laboratory

  54 shared

• James Spencer Lundh

  United States Naval Research Laboratory

  54 shared

• Yiwen Song

  Pennsylvania State University

  46 shared

• Srabanti Chowdhury

  Stanford University

  40 shared

• James Dallas

  Toyota Research Institute

  38 shared

• Marko J. Tadjer

  United States Naval Research Laboratory

  37 shared

Labs

• PSMES BoardPI

  Organization and Board

Education

• Ph.D., Mechanical Engineering

  Georgia Institute of Technology

  2013

• M.S., Automotive Engineering

  Hanyang University

  2007

• B.S., Mechanical Engineering

  Hanyang University

  2005