A terahertz device includes a substrate having a front surface, a conductive layer formed on the front surface, an annular slot formed in the conductive layer, and first and second active elements disposed in the slot to oscillate or detect electromagnetic waves. The conductive layer includes a first electrode defined by the slot, and a second electrode surrounding the first electrode with the slot located in between. The first active element and the second active element are disposed at opposite sides of the first electrode on a straight reference line that extends through a center of the first electrode as viewed in a plan view taken from a direction orthogonal to the front surface. A first distance between opposite ends of the second electrode on the straight reference line is less than a first substrate distance between opposite ends of the substrate on the straight reference line.

A terahertz device includes a substrate having a front surface, a conductive layer formed on the front surface, an annular slot formed in the conductive layer, and first and second active elements disposed in the slot to oscillate or detect electromagnetic waves. The conductive layer includes a first electrode defined by the slot, and a second electrode surrounding the first electrode with the slot located in between. The first active element and the second active element are disposed at opposite sides of the first electrode on a straight reference line that extends through a center of the first electrode as viewed in a plan view taken from a direction orthogonal to the front surface. A first distance between opposite ends of the second electrode on the straight reference line is less than a first substrate distance between opposite ends of the substrate on the straight reference line.