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Thin-film photoconductive antennas using low-temperature GaAs grown on a GaAs substrate of different crystallographic orientation for the generation and detection of terahertz waves.

Name
Vladislav
Surname
Bilyk
Scientific organization
Moscow Technological University (MIREA)
Academic degree
Graduate student
Position
Researcher
Scientific discipline
Physics & Astronomy
Topic
Thin-film photoconductive antennas using low-temperature GaAs grown on a GaAs substrate of different crystallographic orientation for the generation and detection of terahertz waves.
Abstract
Our work is devoted to investigation of photoconductive antennas with delta-doped layers of low temperature LT-GaAs, grown by molecular beam epitaxy at a temperature of 230 ° C on GaAs substrates with the crystallographic orientation of 100 and 111. The method of "pump-probe" THz spectra were obtained with a peak resonance frequency of 0.96 THz. It has been found that the efficiency of generating the THz radiation in the antenna field applied to 111 GaAs substrate is much higher in comparison with the 100 substrate.
Keywords
LT-GaAs, Photoconductive antennas, Terahertz generation
Summary

Photoconductive semiconductor structures based on low-temperature LT-GaAs with planar dipole antennas are the most common devices for the generation and detection of terahertz radiation [1]. Multilayer structures LT-GaAs (low-temperature grown GaAs, the low-temperature "of gallium arsenide) are studied, for the modern high-speed communication applications, for example, in ultrafast optical network switches [2]. The creation of such switches will dramatically increase the speed of data transfer. In addition, this material is used for the rapid and sensitive photodetectors. [3]

The study was made using the optical "pump-probe" technique. As the irradiation source the TiSa laser with the wavelength of 800nm​ was used (photon energy of 1.55 eV), and a pulse duration of 100 fs. The pump pulses passes through a delay line oscillator and focused on the surface generated THz radiation. Further, THz radiation was collect by parabolic mirrors and focused on non-linear ZnTe crystal. On the ZnTe crystal THz sensing and came down. The principle of operation is based on the interaction of terahertz and optical radiation in a nonlinear medium. Due to the non-linearity the optical signal (high frequency) was modulated by terahertz irradiation (low frequency).

The results of THz spectra generated by antennas based on LT-GaAs with different type of substrate are shown in Table 1. It is seen that the efficiency of the antenna on a GaAs substrate 111 section crystallographic 2-fold higher. Most likely, this is due to the high concentration of free electrons in the 111 structure. The electric field accelerate the free charges on the surface and emit in a broad band corresponding to the terahertz frequency range. Spectral width depending on the slice has not changed. The narrow spectrum of THz radiation is most likely associated with limiting the possibility of detecting non-linear ZnTe crystal.

Antenna Type

(Crystallographic section)

The efficiency of THz radiation (au. un.).

Bandwidth

(THz)

100

5,98

2,79

111

12,23

2,79

Thus, it is shown that the efficiency of the antenna TGts- based on LT-GaAs formed on the substrate 111 with the crystallographic section of 2 times more effective than a similar structure made on the substrate 100 with the crystallographic section. 

1.        Venkatesh M. и др. Optical characterization of GaAs photoconductive antennas for efficient generation and detection of Terahertz radiation // Opt. Mater. (Amst). 2014. Т. 36, № 3. С. 596–601.

2.        Obata T. и др. Photoluminescence of nearly stoichiometric LT-GaAs and LT-GaAs/AlAs MQW // J. Cryst. Growth. 2001. Т. 228. С. 112–116.

3.        Mikulics M. и др. Ultrafast low-temperature-grown epitaxial GaAs photodetectors transferred on flexible plastic substrates // Ieee Photonics Technol. Lett. 2005. Т. 17, № 8. С. 1725–1727.