Photoconductive antennas made on low-temperature-grown Be doped InxGa1−xAs (0.45⩽x⩽0.53) have been investigated focusing on the terahertz emission properties. In the antenna of x=0.45, the resistance as high as 3MΩ enabled us to increase the bias field up to 60kV∕cm, and the terahertz waves emitted from the antenna were significantly enhanced. In addition, terahertz waves with the spectral range over 2.5THz and the peak to noise ratio of 45dB were generated and detected using only 1.56μm pulses.

The authors have investigated the dc and terahertz-detection characteristics of the photoconductive antennas made on low-temperature-grown ͑LTG͒ In x Ga 1−x As ͑0.4Ͻ x Ͻ 0.53͒. It was found that the resistivity of the LTG In 0.4 Ga 0.6 As can be as high as 700 ⍀ cm, with which the resistance of the antenna becomes higher than 3 M⍀. Terahertz waves were detected by the antennas with the pulse excitation at 1.56 m, with a spectral range exceeding 3 THz, and a dynamic range of about 55 dB. The results also indicate that the photocarrier dynamics depend on the In content.

We have studied THz detection performance of low-temperature-grown GaAs (LT-GaAs) photoconductive switches gated with 1560-nm-optical pulses. LT-GaAs is annealed in the range of 500-600 IC. Although the sample annealed at 600 IC is most sensitive at frequencies below 1 THz, that annealed at 550 IC is superior to others at higher frequencies than 1 THz.Femtosecond fiber laser can provide portable and stable optical source for terahertz (THz) generation. Since its main wavelength is 1560 nm, development of THz emitters and detectors operative at that wavelength is technological importance [1][2][3][4]. Although photoconductive (PC) antenna prepared on low-temperature-grown GaAs (LT-GaAs) is available for that operation, its sensitivity is one tenth of that for 780-nm-excitation [5]. The detector performance strongly depends on the fabrication process, which should be optimized for 1.5-vim-operation. In the present work, we examine annealing temperature dependence of the LT-GaAs PC switch performance using 1.5-vim fiber laser.1.5 gm fiber laser at a repetition rate of 50 MHz is used as our optical source of 63 fs pulses. We use two kinds of THz emitter; InAs wafer and 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. The detectable maximum frequency of THz waves emitted from InAs and DAST are roughly to be 2 and 7 THz, respectively, in our system. PC dipole antennas are prepared on LT-GaAs grown at 200 'C and annealed at 500, 550, and 600 'C. Figure 1 shows trigger power dependence of THz peak amplitude of THz waves detected by the annealed PC antennas. In this case, InAs is used as THz emitter. The amplitude increases proportionally to the approximate 1.5th power of the trigger power without saturation. The 600-°C-annealing produces the most sensitive detector, and the performance deteriorates as the annealing temperature decreases. In contrast to the above, the antenna annealed at 550 'C showed the maximum sensitivity at higher frequencies than 1 THz. As a result, one can build the 10 20 30 40 Trigger power (mW) Fig. 1: Maximum amplitude of THz detected waves by LTGaAs-based PC antenna annealed at 500, 550, and 600°C.compact THz time domain spectroscopy system with the 1.5-vm fiber laser, which covers the frequency range over 7 THz.In conclusion, the THz detection sensitivity of the PC antenna for 1.5-vim wavelength operation strongly depends on the annealing temperature of LT-GaAs, and also THz frequency itself.

THz-Emission and detection by photoconductive antennas made on low-temperature-grown (LTG) InGaAs with 1.56 gm pulse excitation were investigated. The THz spectra exceeding 2 THz with the peak to noise ratio higher than a hundred were obtained with the InGaAs antennas.

No abstract