In THz time-domain ellipsometry, linearly polarized THz pulses are occurrence on a sample and the electric field strength of the reflected THz waves as a function of time is determined. This multi-angle strategy is utilized to eliminate the systematic mistakes from the amplitude and phase of the discovered THz electrical field in the analysis, which is recently used in THz time-domain ellipsometry. This novel correction approach improves the precision of THz time-domain ellipsometry by over ten times. The maximum carrier concentration that can be assessed is over 2 orders of magnitude greater than generally reported using other THz time-domain strategies.
Schematic image of Terahertz time domain ellipsometry. Credit: Osaka University
In semiconductor device applications, there is an increasing need for semiconductors with extremely high carrier concentrations. The semiconductor product criteria, specifically carrier density and movement, are what mostly determine device efficiency. It is essential to precisely define the provider density and movement of a semiconductor for the advancement of its device applications.
The usage of THz waves, or electromagnetic radiation with wavelengths of around 300 µm and frequency of about 1 THz, in the nondestructive screening of semiconductors has actually been continuously expanding. Free carriers in a material take in THz radiation, that makes it possible to estimate the electrical homes of semiconductors using THz waves.
Scientists at Osaka University, in collaboration with Nippo Precision Co., Ltd., developed a THz time-domain ellipsometry system (Tera Evaluator ® )that extends the variety of carrier concentrations quantifiable by THz waves up to ~ 1020 cm-3 and potentially greater by improving the precision of said optical method. In THz time-domain ellipsometry, linearly polarized THz pulses are incident on a sample and the electric field strength of the reflected THz waves as a function of time is measured. Specifically, the reflected waves polarized in the direction parallel (p) and perpendicular (s) to the plane of incidence are of interest.
The ratio of the p– and s– polarization elements yields information on the electrical permittivity of the sample, enabling for the examination of the carrier density and movement. Unlike THz time-domain spectroscopy, THz time-domain ellipsometry does not need recommendation measurements through an aperture or standard mirror.
This multi-angle strategy is utilized to get rid of the methodical mistakes from the amplitude and stage of the found THz electric field in the analysis, which is recently utilized in THz time-domain ellipsometry. The optimum provider concentration that can be examined is over 2 orders of magnitude higher than usually reported using other THz time-domain techniques.
As a presentation, the scientists evaluated the gallium nitride (GaN) wide-gap semiconductor, which is one of the most technically important semiconductors present in different power electronic devices as well as 5G gadgets. The investigated GaN crystals were made utilizing a crystal growth approach also established at Osaka University called the point-seed strategy by means of the Na-flux method, which produces top quality GaN crystals.
The high-precision THz time-domain ellipsometry system is expected to be widely beneficial in the accurate, noninvasive characterization of various semiconductors with very high provider concentrations.
Recommendation: “Terahertz time-domain ellipsometry with high accuracy for the examination of GaN crystals with provider densities approximately 1020 cm-3” 15 September 2021, Scientific Reports.DOI: https://doi.org/10.1038/s41598-021-97253-z
Funding: METI Monozukuri R&D Support Grant Program for SMEs
