Patent Number: 
Section: claims

1. An optical semiconductor device comprising:a semiconductor film having photoconductive properties, the semiconductor film generating carriers by absorbing light at a light absorption edge of the semiconductor film; anda pair of electrodes for applying an electric field to the semiconductor film causing the carriers to move, the pair of electrodes sandwiching the semiconductor film in a film thickness direction and having a propagating portion extending in a direction opposite the light absorption edge for propagating an electromagnetic wave generated from the semiconductor film by movement of the carriers,wherein the propagating portion is in contact with the semiconductor film and serves as an antenna for radiating into space the electromagnetic wave generated from the semiconductor film, the electromagnetic wave having a frequency in a frequency region of 30 GHz or more and 30 THz or less. 2. An optical semiconductor device according to claim 1, wherein the pair of electrodes are arranged so as to interpose the semiconductor film in the direction perpendicular to the surface of the semiconductor film. 3. An optical semiconductor device according to claim 1, wherein the semiconductor film is a III-V semiconductor film. 4. An optical semiconductor device according to claim 1, wherein overlaid on at least one surface of the semiconductor film is a semiconductor material having a different type of conductivity and a different energy band gap than the semiconductor film. 5. An optical semiconductor device according to claim 1, wherein a transmission path for propagating the electromagnetic wave generated from the semiconductor film is continuously formed, and a metal constituting the transmission path is electrically connected to at least one electrode of the pair of electrodes. 6. An optical semiconductor device according to claim 1, further comprising an optical waveguide for applying light incident on a side surface of the semiconductor film to the region of the semiconductor film to which the electric field is applied. 7. An optical semiconductor device according to claim 2, wherein the electromagnetic wave is generated from the semiconductor film by conducting photoirradiation from above an upper side of the device through spatial propagation to a region of the semiconductor film in a vicinity of an electrode of the pair of electrodes that is arranged toward the upper side of the device relative to a second electrode of the pair of electrodes.