8. Efficient Optical Modulation of Terahertz Metamaterials Utilizing Organic/Inorganic Semiconductor Hybrid Systems

We have utilized highly efficient optical modulation of terahertz (THz) transmission in organic/inorganic semiconductor hybrid system for active control of THz metamaterials. We have investigated highly efficient optical modulation of THz transmission through Si substrate coated with thin layer of organic π-conjugated material, copper phthalocyanine (CuPc) under various continuous-wave (CW) laser light irradiation conditions using THz time-domain spectroscopy. It has been believed that the charge carrier transfer from inorganic semiconductor substrate to π-conjugated material is crucial for efficient optical modulation of THz transmission. We found that the thickness of CuPc layer is a critical parameter to realize high charge carrier density for efficient optical modulation of THz transmission. We also investigated several solution-processable π-conjugated materials instead of CuPc and found that some of them show better modulation efficiency than CuPc. We fabricated a silver split-ring resonator (SRR) array metamaterial on CuPc-coated Si utilizing superfine ink-jet printer and succeeded in obtaining efficient modulation of THz resonant responses of SRR array metamaterials by CW laser light irradiation. Our findings may be utilized to fabricate various types of THz active metamaterials utilizing printing technologies.