The University of Osaka · Engineering
Professor Verdad C. Agulto's research lab specializes in the development and application of terahertz (THz) spectroscopy techniques for nondestructive, contact-free characterization of advanced semiconductors and functional materials. The lab focuses on probing electrical and optical properties—such as carrier density, resistivity, and dielectric response—in wide-bandgap semiconductors like GaN, β-Ga₂O₃, and SiC, as well as biologically relevant materials including hydroxyapatite and calcium oxalate. A key research direction involves utilizing THz time-domain spectroscopy (THz-TDS) and THz time-domain ellipsometry (THz-TDE) for quantitative, wafer-scale mapping of material properties essential for next-generation power and optoelectronic devices. The lab also explores nonlinear THz phenomena, such as third harmonic generation, to advance ultrafast material diagnostics in the terahertz frequency range.
Figures are computed from collected data and may differ slightly.
Gallium nitride (GaN) is one of the most technologically important semiconductors and a fundamental component in many optoelectronic and power devices. Low-resistivity GaN wafers are in demand and actively being developed to improve the performance of vertical GaN power devices necessary for high-voltage and high-frequency applications. For the development of GaN devices, nondestructive characterization of electrical properties particularly for carrier densities in the order of 10<sup>19</sup> c
Homoepitaxial film and semi-insulating bulk β-Ga2O3 with (001) orientation were studied using terahertz time-domain spectroscopy (THz-TDS) in the frequency region from 0.2 to 3.0 THz parallel to the [100] and [010] directions. The static permittivity of the bulk was determined to be 10.0 and 10.4 along the a-axis and b-axis, respectively, and the refractive index values at 0.2 THz are 3.17 and 3.23 for each axis. The electrical resistivity of the epilayer was extracted with good accuracy by empl
We report on the third harmonic generation (THG) in InSb semiconductor irradiated by a terahertz (THz) free electron laser (FEL). The conversion of 4 THz (wavelength 70 µm) FEL outputs into its third harmonic 12 THz was observed. We found that by tuning the sample temperature to 360 K, high conversion efficiency up to 1% can be obtained and is the highest in the THz and FIR regions below 10 THz. We also discuss the observed intensity dependence of the THG with the nonlinear order lower than 3 wh
Terahertz (THz) measurements are increasingly valued for nondestructive testing of materials in power devices and other applications. Hence, there is a growing demand for highly accurate characterization methods in the THz range. Here we demonstrate the application of THz time-domain ellipsometry (THz-TDE) to large-scale, quantitative mapping of semiconductor wafers. While THz-TDE is an established technique, its application in wafer-scale mapping, which is an important process in the semiconduc
Calcium oxalate is the main constituent of kidney stones, and it exists either in monohydrate or dihydrate form. Herein calcium oxalate dihydrate was investigated by Fourier transform infrared (FTIR) spectroscopy in the far-infrared region. The results reveal a characteristic absorption band around 8.5 THz. This finding could be useful in the phase identification of kidney stones which is valuable in understanding the stone formation mechanism.
Phase identification in bones is necessary in understanding the complex bone mineralization process. One technique that is employed in bone classification is infrared spectroscopy. However, most previous reports have focused on the mid-infrared region. It is then interesting to investigate bone components at far-infrared frequencies to find possible unique characteristics that could be useful in bone classification. In this study, we present the far-infrared/terahertz absorption properties of sy
Hydrothermally grown hexagonal wurtzite ZnO microrods coated with polyvinylpyrrolidone (PVP) via an ex-situ method, was successfully synthesized without using complex procedure or experimental setup. FTIR results confirm the presence of different functional groups of PVP at the ZnO surface and the chemical interaction of ZnO with the C=O ligand of the PVP molecule. The presence of PVP molecules prevents the absorption of atmospheric CO 2 by the Zn 2+ ions since PVP chemically interacts with ZnO
Herein we show the terahertz (THz) time-domain ellipsometry investigation of the InSb semiconductor. At room temperature, the carriers of InSb are thermally excited to the conduction band due to its narrow bandgap. We, nevertheless, show that THz ellipsometry can detect subtle differences between carrier densities of undoped and lightly doped InSb bulk semiconductors. The advantage of THz ellipsometry over other THz time-domain spectroscopy techniques is that it does not require reference measur
Kidney stones are mainly composed of calcium oxalate (CaOx) minerals, and the understanding of the polymorphisms of CaOx is essential in establishing the pathogenesis of kidney stone formation. CaOx polymorphs are predominantly calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). In this study, we employ reflection-mode Fourier transform infrared spectroscopy in the far-infrared region to map the spatial distribution of the main CaOx phases in a thin section of kidney stone. A
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