研究目的
To investigate the dielectric response and birefringence of m-plane sapphire substrates in the terahertz frequency region using polarization-sensitive THz time-domain spectroscopy.
研究成果
The m-sapphire substrate exhibits significant orientation-dependent THz response due to birefringence, with a time delay of 480 fs observed between azimuth angles of 45° and 90°. Strong absorptions around 1 THz at specific angles are attributed to low-frequency phonon modes. This research provides insights into the dielectric properties of sapphire substrates, which are crucial for developing III-nitride THz devices.
研究不足
The study is limited to m-plane sapphire substrates; other orientations or materials were not extensively compared. The birefringence value obtained (0.28) is slightly smaller than previously reported values, indicating potential measurement or sample variations. The experimental setup requires a specialized THz TDS system, which may not be widely accessible.
1：Experimental Design and Method Selection:
Polarization-sensitive THz time-domain spectroscopy (TDS) was used in a parallel-polarization configuration to study the dielectric properties of m-sapphire substrates by rotating the sample azimuth angle.
2：Sample Selection and Data Sources:
Commercially available c- and m-plane sapphire wafers (2-inch diameter) from Shinkosa were used. Samples were mounted to cover a 3 mm aperture in a brass holder and loaded in a dry nitrogen-purged box.
3：List of Experimental Equipment and Materials:
Amplified Ti:sapphire laser (
4：2 W pulsed near-IR light at 1 kHz), ZnTe (110) crystals for THz generation and detection, brass holder, dry nitrogen-purged sample box. Experimental Procedures and Operational Workflow:
THz radiation was generated by optical rectification in a ZnTe (110) crystal, focused onto the sample with a
5：5 mm spot size, and detected using free-space electro-optic sampling with a second ZnTe (110) crystal in parallel polarization configuration. The phi angle of the m-sapphire substrate was rotated from 0° to 360°. Data Analysis Methods:
Transmitted THz waveforms were Fourier-transformed to obtain frequency spectra, and time delays and amplitudes were analyzed with respect to azimuth angle.
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