Terahertz wave generation from GaSe crystals and effects of crystallinity

Terahertz (THz)-wave output power generated by GaSe crystals was investigated with respect to crystallinity. GaSe crystals with an epsilon crystal structure have carrier densities of 10¹⁰ or 10¹⁴ cm^-3. According to X-ray diffraction measurements, the two crystals have an almost identical lattice strain, while the lower carrier density crystal has a greater dislocation density than that of the crystal with higher carrier density. At frequencies of less than 1.3 THz, the THz wave output power of the GaSe crystal with the lower carrier density was higher than that of the crystal with the higher density. At frequencies greater than 1.3 THz, the crystal with the lower dislocation had a higher output than the other crystal. Therefore, a GaSe crystal with a low carrier density and few lattice defects should generate more powerful THz waves.