Toshiyuki KAIZU (海津 利行)

The basic photoconductive properties of an InAs/GaAs quantum dot (QD) superlattice have been characterized to develop photoconductive antennas (PCAs) operating with a telecom wavelength excitation for practical terahertz (THz) systems. The multiple-stacked InAs/GaAs QD structure was grown by molecular beam epitaxy and photo-Hall effect measurements were performed under infrared illumination conditions using light-emitting diodes with different emission wavelengths. The results have shown that the sign reversal occurs in the Hall coefficient (RH) as the illumination wavelength changes: RH is negative at 940 nm, and positive at 1550 nm. The photocurrent at 940 nm illumination is ascribed to the electron hole pair generation in QDs, whereas the photocurrent at 1550 nm is dominated by the hole current generated through the midgap states in the structure. The hole dominant photocurrent has been interpreted by a model in which photogenerated electrons are trapped in QDs and the number of mobile electrons are reduced. High dark resistance of the present QD superlattice material provides an advantage for the application to PCA devices. THz wave generation has been demonstrated by the ultrafast 1550 nm pulse excitation of a PCA device fabricated from the QD superlattice.