An anisotropic α-HgS single crystal with giant second-harmonic generation

The exploration of in-plane anisotropic properties is of great significance for fundamental studies and further development of polarization-sensitive optoelectronics. In this study, the synthesis of the chiral material α-HgS via a temperature-oscillation chemical vapor transport process is reported. The (001) plane orientation is well demonstrated by x-ray diffraction. Angle-resolved polarized Raman spectroscopy reveals that α-HgS exhibits strong in-plane anisotropic phonon vibrations. Furthermore, it is demonstrated that the second-harmonic generation (SHG) intensity of α-HgS is highly dependent on both excitation wavelengths and crystallographic orientation, especially with the giant SHG efficiency (134 times that of MoS2). These anisotropic properties make α-HgS an interesting platform for novel polarization-sensitive optoelectronic applications.