Temperature dependence of THz radiation from semi-insulating InP surface

Temperature dependence of the THz radiation from n-, p-, and semi-insulating- (SI-) InP surfaces excited by ultrashort laser pulses has been studied in detail. It is found that the polarity reversal of the waveform occurs at 120 K for SI-InP whereas it does not for n- and p-InP. This result is interpreted in terms of the crossover of the two radiation mechanisms, i.e. the current surge effect due to a built-in surface field and the photo-Dember effect: the former is effective at high temperatures and the latter is effective at low temperatures.