Semiconductor terahertz emitters

Abstract

There is a demand for more efficient sources of electromagnetic radiation in the terahertz (THz, 10 12 Hz) frequency region. One common method of generating THz-frequency radiation is to direct fs pulses of nearinfrared 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.

Investigation of p-GaAsSb as a THz Emitter

“…The rate of increase at first increases with bias, as is the case for GaAs, where a quadratic dependence of radiated THz power on applied bias is observed. 15 Beyond about 25 V applied bias, however, the rate of increase declines, tending toward a linear dependence of the THz power on bias. The reason behind this saturation effect is not known precisely but may be related to an increase in sample resistance or a decrease in mobility due to heating.…”

“…It is much smaller than effects we have observed previously in GaAs. 15 The doped samples were also tested for photoconductivity, but none of them gave a measurable response. This was because they were all highly conductive to begin with, at least an order of magnitude more conductive than the nominally undoped sample.…”

“…4͒ and as is the case for GaAs. 15 The THz emission was next investigated using time-domain spectroscopy. For both the Ag paint and the Au antenna structure, representative time-domain spectra are shown in Fig.…”

“…We have recently investigated the THz emission from Be-doped GaAs. 14,15 In the present work, we extend the investigation to Be-doped GaAsSb.…”

Emission of terahertz-frequency electromagnetic radiation from indium phosphide under excitation by short pulses of near-infrared radiation

“…These include optical rectification, as exhibited by Zinc Telluride (ZnTe) and photoconduction, as exhibited by Gallium Arsenide (GaAs) on which suitable electrodes have been fabricated 1 . A third class of emitters operates according to surface-field effects; the strongest of these to date appears to be InAs 2 .…”