Publication Details

Hargreaves, S., Lewis, R. A. & Henini, M. (2007). Semiconductor terahertz emitters. Microelectronics, MEMS, and Nanotechnology 2007 (pp. 67980Y-1-67980Y-8). Canberra: SPIE.


There is a demand for more efficient sources of electromagnetic radiation in the terahertz (THz, 1012 Hz) frequency region. One common method of generating THz-frequency radiation is to direct fs pulses of near-infrared laser radiation onto a material which then re-radiates. This approach permits coherent pulses of THz radiation to be produced which, for example, may be used for time-domain spectroscopy (TDS). There are three principal mechanisms by which THz radiation is generated under the stimulus of ultra-short pulses: optical rectification (OR) in electro-optic materials, photoconductivity (PC) from materials with suitable electrodes, and surface-field (SF) effects in other cases. The III-V compound semiconductor GaAs doped with the acceptor impurity Be produces relatively small amounts of THz radiation via the OR and SF mechanisms, but relatively large amounts via the PC mechanism. We have studied the PC emission of THz radiation from layers of GaAs(Be) grown epitaxially on GaAs substrates. The THz power generated depends on the bias applied to the electrodes approximately quadratically. This is typical of the PC mechanism. The dependence of the THz power on the power of the pump beam is approximately linear. In general, the THz generated tends to decrease as the doping level increases. If the doping level exceeds the Mott limit and the material becomes highly conductive then the photoconductivity and consequently the THz production are quenched.

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