Sarkisov, Sergey Yu.

Skakunov, M. S.

Tolbanov, Oleg P.

Tyazhev, Anton V.

Zarubin, A. N.

English

Tomsk State University Repository

 2015 25th Int. Crimean Conference “Microwave & Telecommunication Technology” (CriMiCo’2015). 6—12 September, Sevastopol, Crimea  2015: CriMiCo’2015 Org. Com. ISBNs: 978-1-4673-9413-0, 978-1-4673-9414-7, 978-1-4673-9415-4. IEEE Cat. Nr. CFP 15788 455 SI-GaAs<Cr> PHOTOCONDUCTIVE DIPOLE ANTENNAS  FOR TERAHERTZ GENERATION: THE INFLUENCE OF ANTENNA LENGTH AND SHAPE  Sarkisov S. Yu., Skakunov M. S., Tolbanov O. P, Tyazhev A. V., Zarubin A. N. Tomsk State University 36, Lenin Ave., Tomsk, 634050, Russia Tel. +7-3822-413636, e-mail: sarkisov@mail.tsu.ru  Abstract — Photoconductive dipole antennas based on semi-insulating GaAs compensated with Cr (SI-GaAs<Cr>) have been designed and fabricated. Three types of antenna design were tested, namely butterfly, bow-tie and stripline. It was found that at femto-second laser excitation the terahertz radiation in frequency range 0.05-1.5 THz can be generated in the SI-GaAs<Cr> dipole antennas with nonequilibrium carrier lifetimes as high as 100 ns. The stripline antenna with length of 150 µm was found to be the most efficient te-rahertz emitter.   ФОТОПРОВОДЯЩИЕ ДИПОЛЬНЫЕ АНТЕННЫ НА ОСНОВЕ  SI-GaAs<Cr> ДЛЯ ГЕНЕРАЦИИ ТЕРАГЕРЦОВОГО ИЗЛУЧЕНИЯ: ВЛИЯНИЕ ДЛИНЫ И ФОРМЫ АНТЕННЫ   Саркисов С. Ю., Скакунов М. С., Толбанов О. П., Тяжев А. В., Зарубин А. Н. Национальный исследовательский Томский государственный университет 36, пр. Ленина, Томск, 634050, Россия Teл: +7-3822-413636, e-mail: sarkisov@mail.tsu.ru  Аннотация — Разработаны и изготовлены фотопроводящие дипольные антенны на основе полуизолирующего GaAs, компенсированного хромом (SI-GaAs<Cr>). Протестировано три типа антенн: антенна-бабочка, трапециевидная и полосковая. Установлено, что при возбуждении фемтосекундным лазером в антеннах на основе SI-GaAs<Cr> со временем жизни неравно-весных носителей заряда порядка 100 нс может быть генерировано терагерцовое излучение в диапазоне 0.05-1.5 ТГц. Обна-ружено, что наиболее эффективным излучателем является полосковая антенна длиной 150 мкм.   I. Introduction Despite being well known terahertz detectors and emitters for terahertz time-domain spectroscopy (THz-TDS) photoconductive dipole antennas (DAs) still are developed. Role of geometrical configuration, excitation parameters and properties of photoconductive material is studied [1, 2]. The parameters and efficiency of the devices are optimized as well as new types of dipole an-tennas are designed. For example dipole antennas on InGaAs/InAlAs heterostructures for excitation by 1.55 µm lasers have been created [3]. For these lasers, common for optical communications, high resistivity bulk photoconductor materials are relatively difficult to find.  In most of the cases the dipole antennas are fabri-cated on LT-GaAs. This material can possess subpico-second carrier lifetime but requires epitaxial growth technology. In our previous work we studied SI-GaAs<Cr> dipole antennas with antenna length as large as 700 µm to optimize the resonance condition for low terahertz frequencies as the carrier life time is long. We obtained the terahertz emission spectra with clear max-ima about 0.1-0.2 THz [4]. In order to check the influ-ence of the resonance condition and antenna shape in the present work we have fabricated another set of an-tennas with different lengths and of three well-known shapes, namely butterfly, bow-tie and stripline. ll. Main Part The geometrical parameters of the fabricated and tested antennas are given in Fig. 1. The antenna struc-tures (1 µm thick Al layer) were formed on SI-GaAs<Cr> wafers by photolithographic process.  The measurements were done using conventional THz-TDS setup. The 100 fs laser pulses were attenuat-ed and focused onto antenna gap. The incident optical     Fig. 1. Dipole antenna geometrical configurations  (w=10 µm, d =5 µm, A=5 mm). a) Butterfly (l=25-450 µm, L=100 µm) b) Stripline (l=25-150 µm, L=1 mm) c)  Bow-tie (l=25-450 µm). Рис. 1. Геометрические параметры дипольных антенн (w=10 мкм, d =5 мкм, A=5 мм). a) Антенна-бабочка (l=25-450 мкм, L=100 мкм) b) Полосковая антенна (l=25-150 мкм, L=1 мм) c) Трапециевидная антенна (l=25-450 мкм)  2015 25th Int. Crimean Conference “Microwave & Telecommunication Technology” (CriMiCo’2015). 6—12 September, Sevastopol, Crimea  2015: CriMiCo’2015 Org. Com. ISBNs: 978-1-4673-9413-0, 978-1-4673-9414-7, 978-1-4673-9415-4. IEEE Cat. Nr. CFP 15788 456 power was 40-60 mW. The applied voltage was about 18 V. The waveforms were registered by electro-optic sam-pling in a 1 mm thick GaSe crystal.  In the previous study [4] long stripline antennas were tested. As for the Hertzian dipole, the resonance fre-quency for dipole antenna is usually written as 2cnlν = , where n is refractive index of semiconductor wafer, c is the speed of light and l is antenna length. Thus we reduced l values to 25-45 µm to test the possi-bility to get more efficient generation about 1 THz. We compared first the terahertz emission spectra of different antenna types with the largest lengths (Fig. 2). It is seen that for the stripline antenna the spectrum is broader and exceeds the noise level up to 1.5 THz. The stripline configuration is slightly more efficient than the bow-tie. The butterfly geometry is less efficient for SI-GaAs<Cr> dipole antennas (Fig. 2).  Fig. 2. Terahertz emission spectra of the stripline, bow-tie and butterfly dipole antennas with the largest lengths. Рис. 2. Спектры генерации терагерцового излучения для полосковой, трапециевидной и антенны-бабочки с наибольшими длинами When the length of the stripline antenna is reduced to 35 μm the generated terahertz power reduces (Fig. 3). No peak of generation efficiency is observed about 1 THz. The same was observed for the other antenna types. On the other hand when we compared the striline antennas with 150 and 700 µm lengths it was seen that the 150 µm antenna is more efficient (Fig. 4). The emis-sion spectrum of the 700 µm long antenna is shifted to the lower frequencies.   Fig. 3. Comparison of terahertz emission spectra  of 25-35 and 150 µm dipole antennas. Рис. 3. Сравнение спектров генерации терагерцового излучения для дипольных антенн длиной 25-35 и 150 мкм  III. Discussion To our knowledge, there is no model analysis of in-fluence of different dipole antenna configurations on emitted terahertz power presented in literature. Accord-ing to our measurements the stripline configuration, be-ing also the most simple, provides the best terahertz generation efficiency. The spectral efficiency of the an-tenna is determined by parameters of the excitation and material and cannot be radically shifted by resonance condition. The resonance condition is important near the spectral range of efficient antenna operation determined by parameters of the material.   Fig. 4. Terahertz emission spectra of the stripline dipole antennas with lengths of 150 and 700 µm.  Рис. 4. Спектры генерации терагерцового излучения полосковых дипольных антенн длиной 150 и 700 мкм lV. Conclusion It was experimentally found that for the semiconduc-tor material with long carrier lifetimes (100 ns) used to make our dipole antennas the most efficient antenna configuration is stripline with length of 150 µm. Using this SI-GaAs<Cr> antenna configuration it is possible to get terahertz emission spectrum spanning from 0.05 to 1.5 THz. This study was supported by The Tomsk State Uni-versity Academic D.I. Mendeleev Fund Program (grant No 8.2.06.2015). V. References  [1] Miyamaru F, Saito Yu., Yamamoto K., Furuya T., Nishizawa S., Tani M. Dependence of emission of terahertz radiation on geometrical parameters of dipole photoconductive anten-nas. Applied Physics Letters, 2010, vol. 96, pp. 211104-1-3. [2] Shi W., Jia W.-L., Hou L., Xu J.-Z., Zhang X.-C. Terahertz radiation from large aperture bulk semi-insulating GaAs pho-toconductive dipole antenna. Chinese Physics Letters, 2004, vol. 48, pp. 1020-1027. [3] Roehle H., Dietz R.J.B., Hensel H.J., Bottcher J., Kunzel H., Stanze D., Schell M., Sartorius B. Next generation 1.5 µm terahertz antennas: mesa-structuring of InGaAs/InAlAs pho-toconductive layers. Optics Express, 2010, vol. 18, No. 3, pp. 2296-2301. [4] Sarkisov S.Yu., Safiullin F.D., Skakunov M.S., Tolbanov O.P., Tyazhev A.V., Nazarov M.M., Shkurinov A.P. Dipole antennas based on SI-GaAs:Cr for generation and detection of terahertz radiation. Russian Physics Journal, 2013, vol. 53, No 8, pp. 890-898. 

Фотопроводящие дипольные антенны на основе SI-GaAs<Cr> для генерации терагерцового излучения: влияние длины и формы антенны

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Фотопроводящие дипольные антенны на основе SI-GaAs<Cr> для генерации терагерцового излучения: влияние длины и формы антенны

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