arXiv subjects

Changyun Yoo

Publications and source records attributed to Changyun Yoo.

4 recordsLinked to original sources

arXiv2026

Lumped-Element Model of THz HEB Mixer Based on Sputtered MgB2 Thin Film

We present a comprehensive analysis and experimental study of THz hot-electron bolometer (HEB) mixers made from 40-nm-thick sputtered magnesium diboride (MgB2) thin films on high-resistivity silicon substrates. Using a lumped-element bolometric model, we achieve strong quantitative agreement with measurements of conversion gain, noise temperature, and local-oscillator (LO) coupling to the HEB devices. Our analysis shows that the sensitivity of current HEB devices is primarily limited by on-chip optical losses, with both Johnson and thermal-fluctuation noise contributing significantly to the overall noise temperature. Simulations of an optimized device with near-ideal optical coupling suggest that Johnson noise remains a substantial factor even with improved coupling. Further reduction of the noise temperature may require additional suppression of Johnson noise (via improved intrinsic conversion gain) beyond optimizing optical coupling efficiency. We emphasize the importance of accurate modeling to achieve good numerical agreement with experiments, thereby enabling understanding of the causes of sensitivity loss.

cond-mat.supr-con↗

arXiv2025

THz Metal-Mesh Bandpass Filters with Diamond-shaped Apertures for Sensitive THz Receivers

We present high-performance terahertz (THz) metal-mesh bandpass filters developed to mitigate direct detection effects in sensitive THz receivers based on superconducting hot-electron bolometer (HEB) mixers. These metal-mesh filters are free-standing 5-micron thick sheets of copper perforated with a periodic array of diamond-shaped apertures. The simple aperture design minimizes the effect of fabrication (rounding) errors on filter performance, allowing precise engineering of the center frequency (1.5-5.5 THz) while maintaining high (>90 %) peak power transmission at normal incidence and a relatively narrow bandwidth of 5-15 %. Based on finite-element method (FEM) simulation results, we provide simple design equations that can be used for rapid design with high accuracy. The measured transmission profiles of 1.9-THz, 2.5-THz, and 4.7-THz filters show excellent agreement with the simulation results. These filters are compatible with cryogenic operation and can substantially reduce the direct detection effects in HEB mixers.

physics.ins-det↗

arXiv2023

Indium-Bond-And-Stop-Etch (IBASE) Technique for Dual-side Processing of Thin High-mobility GaAs/AlGaAs Epitaxial Layers

We present a reliable flip-chip technique for dual-side processing of thin (<1 micron) high-mobility GaAs/AlGaAs epitaxial layers. The technique allows the fabrication of small (micron-scale with standard UV photolithography) patterned back gates and dual-gate structures on the thin GaAs/AlGaAs films with good alignment accuracy using only frontside alignment. The technique preserves the high-mobility (>10^6 cm^2 /V-s at 2 K) and most (>95%) of the charge density of the 2-dimensional electron gas (2DEG) systems, and allows linear control of the charge density with small (< 1 V) electrostatic gate bias. Our technique is motivated by a novel THz quantum-well detector based on intersubband transitions in a single, wide GaAs/AlGaAs quantum well, in which a symmetric, well-aligned dual-gate structure (with a typical gate dimension of ~5 micron by 5 micron) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch (IBASE) technique, we realize such dual-gate structure on 660-nm thick GaAs/AlGaAs epitaxial layers that contain a modulation-doped, 40-nm wide, single square quantum well. By independently controlling the charge density and the DC electric field set between the gates, we demonstrate robust tuning of the intersubband absorption behavior of the 40-nm quantum well near 3.44 THz at 30 K.

physics.ins-det↗

arXiv2019

Demonstration of a Tunable Antenna-Coupled Intersubband Terahertz (TACIT) Mixer

A fast, voltage-tunable terahertz mixer based on the intersubband transition of a high-mobility 2-dimensional electron gas (2DEG) has been fabricated from a single 40 nm GaAs-AlGaAs square quantum well heterostructure. The device is called a Tunable Antenna-Coupled Intersubband Terahertz (TACIT) mixer, and shows tunability of the detection frequency from 2.52 THz to 3.11 THz with small (< 1 V) top gate and back gate voltage biases. Mixing at 2.52 THz has been observed at 60 K with a -3dB intermediate frequency (IF) bandwidth exceeding 6 GHz.

physics.ins-det↗