Fig. 1. Characterization of the GaTe crystal by (a) an XRD spectrum; (b) a Raman spectrum with a laser wavelength of 785 nm; (c) optical absorption spectra, with the excitonic absorption observed around 1.62 eV. Inset in (c) shows square root of the absorption as a function of energy, where the linear extrapolation reveals an optical bandgap of 0.76 eV, associated with an indirect bandgap; (d) PL spectrum of GaTe at 10 K under 488 nm laser excitation.

Fig. 2. Experimental setup of the THz emission spectroscopy system used. (a) Schematic illustration. GTP, Glan–Taylor prism; HWP, half-wave plate; WGP, wire-grid polarizer. (b) Sample in transmission configuration. XYZ represents the Cartesian laboratory CS.

Fig. 3. Typical THz waveform in (a) time domain and (b) frequency domain generated from layered GaTe.

Fig. 4. X component of the generated THz waveforms from GaTe under p-polarized (P_in) and s-polarized (S_in) excitation with (a) 0° and (b) 40° incident angle; (c) X component of generated THz waveforms from GaTe under 40°, −40°, 0° incidences; (d) peak-to-valley values of THz pulses from GaTe as a function of incident angle.

Fig. 5. THz radiation peak-valley amplitude as a function of (a) azimuthal angle and (b) pump polarization angle under normal incidence. The experimental data and the fitting according to the OR and PS model are depicted by black squares and solid lines, respectively.

Fig. 6. THz peak-valley amplitude as a function of (a) azimuthal angle and (b) pump polarization angle under 40° incident angle. The experimental data and the fitting according to the OR and PS model are depicted by black squares and solid lines, respectively.

Fig. 7. Pump fluence dependence of THz peak-to-valley amplitude generated from GaTe at (a) 0° and (b) 40° incident angle.

Table 1. Resistivity Anisotropy of Bulk GaTe Surface