Enhancement of THz emission from semiconductor devices

We have studied the emission of coherent terahertz (THz) frequency electromagnetic pulses from semiconductor surfaces. Collimated beams of THz radiation are observed from surface-field emitters and the efficiency of these emitters is shown to be improved by (a) modifying the effective refractive index at the surface of the emitter and (b) reorienting the THz dipole with respect to the surface. A /spl sim/ 20/spl times/ enhancement in emitted THz power was seen in a GaAs/InAs prism emitter.