860 µW Terahertz Power Generation from Graded Composition InGaAs Photoconductive Nanoantennas

We present a record-high-power, telecommunication-compatible photoconductive terahertz emitter fabricated on an epitaxial InGaAs layer with a linearly graded Indium composition. The graded Indium composition induces a strong built-in electric field throughout the entire photoconductive layer, which drifts all photocarriers to an array of nanoantennas for efficient terahertz generation. The nanoantenna structure is designed to excite surface plasmon waves when excited by the optical pump beam to provide strong confinement of the photocarriers in close proximity to the nanoantennas where the built-in field strength is maximized. By eliminating the undesired excessive dark current that exists in conventional photoconductive terahertz emitters, a highly reliable operation is achieved without the need for any external bias voltage. We demonstrate the highest generated terahertz power of 860 µW compared to the state-of-the-art telecommunication-compatible photoconductive terahertz emitters.