THz Semiconductor Devices is semiconductor-based components generating, detecting, modulating terahertz radiation (0.1-10 THz), enabling imaging, sensing, and communication applications — THz bridges electronics and photonics. THz Band 0.1-10 THz corresponds to wavelengths 30-3000 micrometers. Between microwave and infrared. Generation quantum cascade lasers (QCLs), resonant tunneling diodes (RTDs), photomixers generate THz. Detection Schottky diodes, bolometers, superconducting microbolometers detect THz. High sensitivity. RTD Oscillators resonant tunneling diodes oscillate due to negative differential resistance. Compact THz sources. Frequency Tuning bias voltage tunes RTD oscillation frequency. QCL (Quantum Cascade Laser) nested quantum wells; electrons cascade, emitting THz photons. Coherent THz source. Modulation electro-optic modulators change THz beam intensity. Waveguides metal or plastic waveguides guide THz. Planar antennas couple to free space. Antennas log-periodic, dipole, horn antennas for THz radiation. Imaging THz imaging penetrates many materials (textiles, paper, cardboard). Non-ionizing. Security applications (screening). Sensing THz spectroscopy identifies materials (absorption fingerprints). Drug identification, explosives detection. Communication THz wireless communication high bandwidth. Limited range (absorption in atmosphere). Heterodyne Detection downconvert THz to lower frequency for sensitive detection. Schottky Mixers Schottky diodes mix signal and local oscillator. Noise Figure THz detectors have high noise figure (limited by quantum noise). Cooling Requirements some THz devices require cryogenic cooling (QCLs, bolometers). Room Temperature RTDs, photomixers operate room temperature. Integration on-chip THz circuits combining sources, modulators, antennas. Silicon photonics + electronics. Fabrication semiconductor processes (GaAs, InP, silicon) compatible. Bandwidth THz devices inherently broadband. Semiconductor THz devices enable applications from imaging to communication.