PHOTOSIGNAL ENHANCEMENT IN AL-GAAS DIODES DUE TO SURFACE-PLASMONS ANDGUIDED-WAVE MODES

Light of wavelength 632.8 nm and p-polarization is incident on a prism -air gap (varied from 0.7 to 7 mum)-Al-GaAs arrangement. Both the phot osignal generated by the Schottky diode and the reflectance are measur ed as a function of the internal angle of incidence in the prism. Ther e is significant, well-defined enhancement of the photosignal, up to a factor of approximately 7.5, associated with two different types of e nhanced absorption modes. For air gaps < 1.5 mum there is photosignal enhancement due to an enhanced absorption feature (reflectance dip) th at occurs at an angle of incidence just above critical angle in the pr ism; this feature corresponds to the excitation of a surface plasmon p olariton at the Al-air interface. For air gaps > 1 mum there are betwe en one and ten photoresponse peaks at input angles less than the criti cal angle. The corresponding enhanced absorption features are due to l eaky guided wave modes set up in the air gap.