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A Study of Emission Power and Spectrum of LT-GaAs Based THz Photoconductive Antennas
Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 73 (2015) 54 – 58
4th h International Confereence Photon nics and Info formation Optics, O PhIO O 2015, 28-330 January 2015 2
A study oof emisssion pow wer and sspectrum m of LT-GaAs baased TH Hz photo oconducctive anteennas S.A A. Savinovb, Yu.A. Mityagina,b, A A.A .Chisttyakova, K..I .Kozlovsskya, a Yuu.A. Kuzishhchin *, V.A. Krivennkova, V.I .Egorkinc, I.P. I Kazako kovb a
National N Researcch Nuclear University MEPhI (Mo oscow Engineerinng Physics Institute), Kashirskoye shosse 31, Moscoow, 115409, Russsia b P.N.Lebedev Physiical Institute of Russian Academy oof Sciences, Leniinskii pr. 53, 1199 991, Moscow, Rus ussia c Nationaal Research Univversity of Electron nic Technology (M MIET),4806 proeezd 5, Zelenograd d, Moscow, 1244998 Russia
Absttract Emisssion spectra off LT-GaAs phootoconductive antennas a basedd on epitaxial films f of "low-temperature" gaallium arsenidee (LTGaAs) are measuredd in the teraherttz frequency reg gion by the Fouurier transform spectroscopy. © Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license 015The TheAuthors. Authorrs. Published y Elsevier © 2015 20 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer--review under rresponsibility of the National Research R Nucleear University MEPhI M (Moscow w Engineering PPhysics Institutte). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Keyw words: low-tempeerature gallium arsenide; photoexcited carriers; phootoconductive anttennas; terahertz radiation.
1. In ntroduction The T recent advvent of high-ppower pulsed lasers, in paarticular, thosee with femtossecond pulsess (1 fs = 10¡1 15 s), open ned the way too develop com mpact generattors and detecctors of broad dband teraherttz (THz) radiaation, based on o the interraction of laser radiation with w matter [D D. Dragomann et al. (2004 4)]. Photocond ductive antenn nnas (PCA) [D D. H. Austton et al. (1984)] or nonlinnear optical crystals c [Q.W Wu et al. (1996 6)] are comm monly used as active conveersion elem ments. From thhe viewpoint of the effcien ncy of the opptical_teraherttz conversion,, the former ccase appears more prefe ferable [Y. Caai et al.(1998)), Y. C. Shen n et al. (2004))]. Currently, gallium arsen nide grown bby molecular-b beam epitaaxy at lower ttemperatures T < 300 oC is the most acctively studied d material for photoconduct ctive antennas. The best structures bbased on "low w-temperature" gallium aarsenide (LT--GaAs) exhib bit subpicoseccond lifetimees of obilities (~1003 cm2/V·s), high h dark resistivities and breakdown fields f noneequilibrium carriers, relativvely good mo
* Corresponding C autthor. Tel.: +7-9166-00-84-38. E-mail E address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) doi:10.1016/j.phpro.2015.09.121
S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
(~105 V/cm) [S. Gupta et al. (1991), L. Hou u et al. (2013))]. It should be b noted that properties p of pparticular LT--GaAs uctures stronglly depend on growth g and su ubsequent annnealing conditiions. Thereforre, the overwhhelming majorrity of stru worrks on LT-GaaAs is devotedd to studies off the photoex cited carrier relaxation r dyn namics, perforrmed using vaarious "pu ump-probe" tecchniques [Y. Cai C et al. (199 98), Y. C. Sheen et al. (2004 4), S. Gupta et al. (1991), P.. A. Loukakoss et al. (200 02), A. A. Passtor et al. (2012)]. In I the previouus work [T. M. Burbaev et al. (2013))], we describ bed technolog gical operatioons of growth h and subsequent anneaaling of epitaxxial LT-GaAss films and prresented the results r of strucctural studies.. The results of the pho otoexcited carrrier dynamicss studies weree reported in [[A.A. Gorbatssevich et al. (2015)]. This ppaper is devo oted to the study of the L LT-GaAs-baseed PCA emisssion spectra bby Fourier tran nsform spectro oscopy in the tterahertz regio on. 2. Electric E and sspectral charaacteristics of photoconducctive antenna as The T electrical properties of LT-GaAs film ms and spectraal characteristtics of photoco onductive ante tennas (PCAs)) were stud died on samplles prepared by b photolithog graphy with pplanar (V-Au metallization 0.6 μm thickk) contact areaas and anteenna elementss of various shapes s (Fig. 1 (a)). The sam mples were placed p on speccial panels inn front of a th hrough holee~4mm in diiameter, whicch made it possible p to m measure teraheertz (THz) raadiation geneerated by PCA As in tran nsmission modde, i.e., from the crystallin ne GaAs subsstrate side. Du uring measureements, the paanel with fou ur pincon ntacts was inseerted into a coorresponding socket with a standard SM MA plug at the output. PCA contact areass were con nnected with conducting patths on the panel by thermouultrasonic microwelding. ɚ)
Fig. 1. (a) Microographs of the fabbricated photocon nductive stripline (SL) and bow-tiee (BT) antennas on o the LT-GaAs llayer. (b) Measurred dark I_V V characteristics oof photoconductiv ve antennas.
Preliminarily, P the current--voltage characteristics off fabricated LT-GaAs L sam mples were m measured at room tem mperature. Thee setup includded an adjustable stabilizeed voltage sou urce and a dcc voltage metter determinin ng the circcuit current ussing a resistorr (~15 kǷ) co onnected in seeries with thee sample undeer study. Figuure 1 (b) show ws the dark k currents of fabricated strripline and bo ow-tie (Fig. 1 (a)) PCAs, measured m as fu unctions of thhe bias voltag ge Vdc app plied to the strructure in the range of 0–50 0 V. The charracteristic dark k resistances of the samplees under study y were ~10 09 Ƿ, and estim mated resistiviity of the LT-G GaAs films w were about ȡdaark ~ 3·106 Ƿ ·ɫɫm.
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S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
ull squares) of stri ripline photocond ductive antennas based b on LT-GaA As as function of the t Fiig. 2. The emissioon power (squarees) and current (fu bias voltagge. The similar chharacteristics of PCA manufacturedd by Zomega com mpany (circles and full circles) aree also shown
The T total emiission power of THz rad diation was measured wiith a pyroeleectric detectoor and high-sspeed supeerconducting bbolometer witth a time resollution of ~ 5 nns. The measu ured THz pow wer of strip-linne photocondu uctive anten nnas and the current througgh the antennaa as a functionn of applied bias b voltage arre shown in FFig. 2. Similarr data obtaained for one of the best of o the PCAs manufactured m by Zomega company on semi-insulatiing GaAs aree also show wn in Fig. 2. Itt should be nnoted that the ratio (THz Power P / currennt) of investigated antennaas significantlly exceeds similar valu ues for Zomega antennas. Inn particular, fo or Udc = 30 V and femtoseccond excitation n power of 500 mW, this vallue is abou ut 60 mV / mA A, while for Zomega Z antenn na - only 5.2 m mV / mA. Of course, c there should s be takeen into accoun nt the diffeerence in anteenna geometrries, as well as a significantlly smaller illu uminated areaa of our stripp-line antenn nas as com mpared with thhat of Zomegaa ones, but, neevertheless, it is evident thaat the effectiv veness of the sstudied antenn nas is high h enough.
Fig.3. Schematic diagraam of the setup fo or measuring the emission spectraa of fabricated photoconductive anntennas.
S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
The T emission spectra of thhe PCAs undeer study weree measured in n air using a "Grubb-Parsoons MK-3" Fourier inteerferometer. T The complete schematic s diag gram of the seetup is shown n in Fig. 4. Op ptical radiationn of the Ti:Sa laser, focu used by a lenss on the LT-G GaAs layer reg gion between electrodes, ex xcited photocu urrent pulses (with an amp plitude prop portional to thhe applied vooltage Vdc) in the antenna, which, in turn n, caused gen neration of TH Hz radiation pulses. p This radiation em merged to freee space throug gh the substraate, passed through a filter cutting scatteered laser rad diation d, being colleccted by parabbolic mirror PM1 P into a coollimated beam m, was directed to the Fouurier interfero ometer and inpu ut.
Fig.4. (ɚ) Em mission spectrum m of photoconducttive antennas bas ed on LT-GaAs. The inset shows the tabulated norm rmal conditions transmission sspectrum of atmoosphere. (b) Emission spectrum off Zomega photoco onductive antenna a based on semi-iinsulating GaAs.
The T interferom meter operatedd in step-scan mode, implem mented by mo oving the mob bile interferom meter mirror using a miccrometer screw w rotated by the step mottor. As a beaam splitter, a Mylar film 12.5 1 μm thickk was used, which w prov vided a signal maximum at a a frequency y of 105 cm¡11 (3.3 THz). After A passing through interfferometer, thee THz radiiation was foccused by parabbolic mirror PM2 P on the enntrance window of a german nium bolometter cooled by liquid heliium. The signnal from the bolometer b preamplifier outpput was fed to an SR830 lock-in l ampliffier (laser rad diation wass modulated bby a mechaniccal chopper with w a frequenccy of 315 Hz)), then it was digitized by aan analog-to-d digital con nverter (ADC)) and arrived at the compu uter for proceessing interfeerogram and restoring r the emission speectrum usin ng the fast Fourier trannsform algoriithm. The F Fourier specttrometer was controlled by a stand--alone miccroprocessor uunit including an ADC, steep motor contrrol unit, and the t system off data exchangge with an ex xternal com mputer. Figure F 4a show ws the spectruum of THz raadiation generrated by fabriccated photoco onductive anteennas at an av verage optiical illuminatiion (800 nm) power of ~10 00 mW and ap applied direct voltage Vdc = 50 V. In thiis case, the av verage currrents in striplline and bow--tie antennas were 180 andd 30 μA, resp pectively. Thee spectra werre measured with w a reso olution of ~1 ccm-1. In Fig.44b the measureed emission sppectrum of Zo omega antennaa is also show wn We W can see that the meaasured spectra exhibit thee broad contiinuous band; the most paart of radiatiion is con ncentrated in thhe range of 5--60 cm-1 (0.15-1.8 THz). Thhe peaked stru ucture observeed in the specttra is mainly caused c by atmospheric a w water vapor abbsorption, whiich is confirm med by a comp parison of the measured m curvves with the ty ypical atm mospheric transsmission specctrum shown in n the inset. Thus, T the emisssion characteeristics of pho otoconductive antennas baseed on the epittaxial films off "low-temperature" galllium arsenide were studied.. The measureed emission sppectra exhibit pronounced maxima m in thee terahertz region. It wass shown that the antenna configuration n has a signifficant effect on o the radiation spectrum shape. For th he SL anteenna, the intennsity maximum m is higher an nd the frequenncy is lower th han those of th he BT antennaa operating at lower
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S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
currents. It is important that antenna emitters were fabricated using the standard planar microelectronic technology, which offers prospects for constructing integrated THz phased antenna arrays with controllable directional patterns. Acknowledgements This work was supported by the Russian Foundation for Basic Research (projects No. 15-02-08521a and 15-0209055a), the Ministry of Education and Science of Russia (State contract no. 14.427.11.0004), and the Basic Research Program of the Presidium of the Russian Academy of Sciences no. 1 "Nanostructures: Physics, Chemistry, Biology, Fundamentals of Technologies". References Auston, D.H., Cheung, K P., Smith, P.R., 1984. Picosecond photoconducting Hertzian dipoles. Appl. Phys. Lett. 45, 284. Burbaev, T. M., Gorbatsevich, A.A., Egorkin, V.I., et al., 2013. Comprehensive study of structural and optical properties of LT-GaAs epitaxial structures. Bull. of the Lebedev Physics Institute 40, 219. Cai, Y., Brener, I., Lopata, J., et al., 1998. Coherent terahertz radiation detection: Direct comparison between free-space electro-optic sampling and antenna detection. Appl. Phys. Lett. 73, 444. Dragoman, D., Dragoman, M., 2004. Terahertz fields and applications. Prog. Quantum Electron. 28, 1-66. Gorbatsevich, A.A., Egorkin, V.I., Kazakov, I.P., et. al., 2015. Dynamic characteristics of “low-temperature” gallium arsenide for terahertz-range generators and detectors. Bull. of the Lebedev Physics Institute. 42(5), 121-126. Gupta, S., Frankel, M.Y., Valdmanis, J.A., et al., 1991. A common method to reduce the minority carrier lifetime and radiation is low temperature growth of GaAs layers. Appl. Phys. Lett. 59, 3276. Hou, L., Shi, W., 2013. An LT-GaAs terahertz photoconductive antenna with high emission power, low noise, and good stability. IEEE Trans. Electron Devices. 60, 1619. Loukakos, P.A., Kalpouzos, C., Perakis, I.E., et al., 2002. The role of As precipitates on ultrafast electron trapping in low-temperature-grown GaAs and AlGaAs alloys. J. Appl. Phys. 91, 9863. Pastor, A.A., Serdobintsev, P.Yu., Chaldyshev, V.V., 2012. Experimental evaluation of the carrier lifetime in GaAs grown at low temperature. Semiconductors. 46, 619-621. Shen, Y.C., Upadhya, P.C., Beere, H.E., et al., 2004. Generation and detection of ultrabroadband terahertz radiation using photoconductive emitters and receivers. Appl. Phys. Lett. 85, 164. Wu, Q., Zhang, X.-C., 1996. Design and characterization of travelling-wave electroopticTHz sensors. IEEE J. Sel. Top. Quantum Electron. 3, 693.
ScienceDirect Physics Procedia 73 (2015) 54 – 58
4th h International Confereence Photon nics and Info formation Optics, O PhIO O 2015, 28-330 January 2015 2
A study oof emisssion pow wer and sspectrum m of LT-GaAs baased TH Hz photo oconducctive anteennas S.A A. Savinovb, Yu.A. Mityagina,b, A A.A .Chisttyakova, K..I .Kozlovsskya, a Yuu.A. Kuzishhchin *, V.A. Krivennkova, V.I .Egorkinc, I.P. I Kazako kovb a
National N Researcch Nuclear University MEPhI (Mo oscow Engineerinng Physics Institute), Kashirskoye shosse 31, Moscoow, 115409, Russsia b P.N.Lebedev Physiical Institute of Russian Academy oof Sciences, Leniinskii pr. 53, 1199 991, Moscow, Rus ussia c Nationaal Research Univversity of Electron nic Technology (M MIET),4806 proeezd 5, Zelenograd d, Moscow, 1244998 Russia
Absttract Emisssion spectra off LT-GaAs phootoconductive antennas a basedd on epitaxial films f of "low-temperature" gaallium arsenidee (LTGaAs) are measuredd in the teraherttz frequency reg gion by the Fouurier transform spectroscopy. © Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license 015The TheAuthors. Authorrs. Published y Elsevier © 2015 20 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer--review under rresponsibility of the National Research R Nucleear University MEPhI M (Moscow w Engineering PPhysics Institutte). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Keyw words: low-tempeerature gallium arsenide; photoexcited carriers; phootoconductive anttennas; terahertz radiation.
1. In ntroduction The T recent advvent of high-ppower pulsed lasers, in paarticular, thosee with femtossecond pulsess (1 fs = 10¡1 15 s), open ned the way too develop com mpact generattors and detecctors of broad dband teraherttz (THz) radiaation, based on o the interraction of laser radiation with w matter [D D. Dragomann et al. (2004 4)]. Photocond ductive antenn nnas (PCA) [D D. H. Austton et al. (1984)] or nonlinnear optical crystals c [Q.W Wu et al. (1996 6)] are comm monly used as active conveersion elem ments. From thhe viewpoint of the effcien ncy of the opptical_teraherttz conversion,, the former ccase appears more prefe ferable [Y. Caai et al.(1998)), Y. C. Shen n et al. (2004))]. Currently, gallium arsen nide grown bby molecular-b beam epitaaxy at lower ttemperatures T < 300 oC is the most acctively studied d material for photoconduct ctive antennas. The best structures bbased on "low w-temperature" gallium aarsenide (LT--GaAs) exhib bit subpicoseccond lifetimees of obilities (~1003 cm2/V·s), high h dark resistivities and breakdown fields f noneequilibrium carriers, relativvely good mo
* Corresponding C autthor. Tel.: +7-9166-00-84-38. E-mail E address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) doi:10.1016/j.phpro.2015.09.121
S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
(~105 V/cm) [S. Gupta et al. (1991), L. Hou u et al. (2013))]. It should be b noted that properties p of pparticular LT--GaAs uctures stronglly depend on growth g and su ubsequent annnealing conditiions. Thereforre, the overwhhelming majorrity of stru worrks on LT-GaaAs is devotedd to studies off the photoex cited carrier relaxation r dyn namics, perforrmed using vaarious "pu ump-probe" tecchniques [Y. Cai C et al. (199 98), Y. C. Sheen et al. (2004 4), S. Gupta et al. (1991), P.. A. Loukakoss et al. (200 02), A. A. Passtor et al. (2012)]. In I the previouus work [T. M. Burbaev et al. (2013))], we describ bed technolog gical operatioons of growth h and subsequent anneaaling of epitaxxial LT-GaAss films and prresented the results r of strucctural studies.. The results of the pho otoexcited carrrier dynamicss studies weree reported in [[A.A. Gorbatssevich et al. (2015)]. This ppaper is devo oted to the study of the L LT-GaAs-baseed PCA emisssion spectra bby Fourier tran nsform spectro oscopy in the tterahertz regio on. 2. Electric E and sspectral charaacteristics of photoconducctive antenna as The T electrical properties of LT-GaAs film ms and spectraal characteristtics of photoco onductive ante tennas (PCAs)) were stud died on samplles prepared by b photolithog graphy with pplanar (V-Au metallization 0.6 μm thickk) contact areaas and anteenna elementss of various shapes s (Fig. 1 (a)). The sam mples were placed p on speccial panels inn front of a th hrough holee~4mm in diiameter, whicch made it possible p to m measure teraheertz (THz) raadiation geneerated by PCA As in tran nsmission modde, i.e., from the crystallin ne GaAs subsstrate side. Du uring measureements, the paanel with fou ur pincon ntacts was inseerted into a coorresponding socket with a standard SM MA plug at the output. PCA contact areass were con nnected with conducting patths on the panel by thermouultrasonic microwelding. ɚ)
Fig. 1. (a) Microographs of the fabbricated photocon nductive stripline (SL) and bow-tiee (BT) antennas on o the LT-GaAs llayer. (b) Measurred dark I_V V characteristics oof photoconductiv ve antennas.
Preliminarily, P the current--voltage characteristics off fabricated LT-GaAs L sam mples were m measured at room tem mperature. Thee setup includded an adjustable stabilizeed voltage sou urce and a dcc voltage metter determinin ng the circcuit current ussing a resistorr (~15 kǷ) co onnected in seeries with thee sample undeer study. Figuure 1 (b) show ws the dark k currents of fabricated strripline and bo ow-tie (Fig. 1 (a)) PCAs, measured m as fu unctions of thhe bias voltag ge Vdc app plied to the strructure in the range of 0–50 0 V. The charracteristic dark k resistances of the samplees under study y were ~10 09 Ƿ, and estim mated resistiviity of the LT-G GaAs films w were about ȡdaark ~ 3·106 Ƿ ·ɫɫm.
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S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
ull squares) of stri ripline photocond ductive antennas based b on LT-GaA As as function of the t Fiig. 2. The emissioon power (squarees) and current (fu bias voltagge. The similar chharacteristics of PCA manufacturedd by Zomega com mpany (circles and full circles) aree also shown
The T total emiission power of THz rad diation was measured wiith a pyroeleectric detectoor and high-sspeed supeerconducting bbolometer witth a time resollution of ~ 5 nns. The measu ured THz pow wer of strip-linne photocondu uctive anten nnas and the current througgh the antennaa as a functionn of applied bias b voltage arre shown in FFig. 2. Similarr data obtaained for one of the best of o the PCAs manufactured m by Zomega company on semi-insulatiing GaAs aree also show wn in Fig. 2. Itt should be nnoted that the ratio (THz Power P / currennt) of investigated antennaas significantlly exceeds similar valu ues for Zomega antennas. Inn particular, fo or Udc = 30 V and femtoseccond excitation n power of 500 mW, this vallue is abou ut 60 mV / mA A, while for Zomega Z antenn na - only 5.2 m mV / mA. Of course, c there should s be takeen into accoun nt the diffeerence in anteenna geometrries, as well as a significantlly smaller illu uminated areaa of our stripp-line antenn nas as com mpared with thhat of Zomegaa ones, but, neevertheless, it is evident thaat the effectiv veness of the sstudied antenn nas is high h enough.
Fig.3. Schematic diagraam of the setup fo or measuring the emission spectraa of fabricated photoconductive anntennas.
S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
The T emission spectra of thhe PCAs undeer study weree measured in n air using a "Grubb-Parsoons MK-3" Fourier inteerferometer. T The complete schematic s diag gram of the seetup is shown n in Fig. 4. Op ptical radiationn of the Ti:Sa laser, focu used by a lenss on the LT-G GaAs layer reg gion between electrodes, ex xcited photocu urrent pulses (with an amp plitude prop portional to thhe applied vooltage Vdc) in the antenna, which, in turn n, caused gen neration of TH Hz radiation pulses. p This radiation em merged to freee space throug gh the substraate, passed through a filter cutting scatteered laser rad diation d, being colleccted by parabbolic mirror PM1 P into a coollimated beam m, was directed to the Fouurier interfero ometer and inpu ut.
Fig.4. (ɚ) Em mission spectrum m of photoconducttive antennas bas ed on LT-GaAs. The inset shows the tabulated norm rmal conditions transmission sspectrum of atmoosphere. (b) Emission spectrum off Zomega photoco onductive antenna a based on semi-iinsulating GaAs.
The T interferom meter operatedd in step-scan mode, implem mented by mo oving the mob bile interferom meter mirror using a miccrometer screw w rotated by the step mottor. As a beaam splitter, a Mylar film 12.5 1 μm thickk was used, which w prov vided a signal maximum at a a frequency y of 105 cm¡11 (3.3 THz). After A passing through interfferometer, thee THz radiiation was foccused by parabbolic mirror PM2 P on the enntrance window of a german nium bolometter cooled by liquid heliium. The signnal from the bolometer b preamplifier outpput was fed to an SR830 lock-in l ampliffier (laser rad diation wass modulated bby a mechaniccal chopper with w a frequenccy of 315 Hz)), then it was digitized by aan analog-to-d digital con nverter (ADC)) and arrived at the compu uter for proceessing interfeerogram and restoring r the emission speectrum usin ng the fast Fourier trannsform algoriithm. The F Fourier specttrometer was controlled by a stand--alone miccroprocessor uunit including an ADC, steep motor contrrol unit, and the t system off data exchangge with an ex xternal com mputer. Figure F 4a show ws the spectruum of THz raadiation generrated by fabriccated photoco onductive anteennas at an av verage optiical illuminatiion (800 nm) power of ~10 00 mW and ap applied direct voltage Vdc = 50 V. In thiis case, the av verage currrents in striplline and bow--tie antennas were 180 andd 30 μA, resp pectively. Thee spectra werre measured with w a reso olution of ~1 ccm-1. In Fig.44b the measureed emission sppectrum of Zo omega antennaa is also show wn We W can see that the meaasured spectra exhibit thee broad contiinuous band; the most paart of radiatiion is con ncentrated in thhe range of 5--60 cm-1 (0.15-1.8 THz). Thhe peaked stru ucture observeed in the specttra is mainly caused c by atmospheric a w water vapor abbsorption, whiich is confirm med by a comp parison of the measured m curvves with the ty ypical atm mospheric transsmission specctrum shown in n the inset. Thus, T the emisssion characteeristics of pho otoconductive antennas baseed on the epittaxial films off "low-temperature" galllium arsenide were studied.. The measureed emission sppectra exhibit pronounced maxima m in thee terahertz region. It wass shown that the antenna configuration n has a signifficant effect on o the radiation spectrum shape. For th he SL anteenna, the intennsity maximum m is higher an nd the frequenncy is lower th han those of th he BT antennaa operating at lower
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S.A. Savinov et al. / Physics Procedia 73 (2015) 54 – 58
currents. It is important that antenna emitters were fabricated using the standard planar microelectronic technology, which offers prospects for constructing integrated THz phased antenna arrays with controllable directional patterns. Acknowledgements This work was supported by the Russian Foundation for Basic Research (projects No. 15-02-08521a and 15-0209055a), the Ministry of Education and Science of Russia (State contract no. 14.427.11.0004), and the Basic Research Program of the Presidium of the Russian Academy of Sciences no. 1 "Nanostructures: Physics, Chemistry, Biology, Fundamentals of Technologies". References Auston, D.H., Cheung, K P., Smith, P.R., 1984. Picosecond photoconducting Hertzian dipoles. Appl. Phys. Lett. 45, 284. Burbaev, T. M., Gorbatsevich, A.A., Egorkin, V.I., et al., 2013. Comprehensive study of structural and optical properties of LT-GaAs epitaxial structures. Bull. of the Lebedev Physics Institute 40, 219. Cai, Y., Brener, I., Lopata, J., et al., 1998. Coherent terahertz radiation detection: Direct comparison between free-space electro-optic sampling and antenna detection. Appl. Phys. Lett. 73, 444. Dragoman, D., Dragoman, M., 2004. Terahertz fields and applications. Prog. Quantum Electron. 28, 1-66. Gorbatsevich, A.A., Egorkin, V.I., Kazakov, I.P., et. al., 2015. Dynamic characteristics of “low-temperature” gallium arsenide for terahertz-range generators and detectors. Bull. of the Lebedev Physics Institute. 42(5), 121-126. Gupta, S., Frankel, M.Y., Valdmanis, J.A., et al., 1991. A common method to reduce the minority carrier lifetime and radiation is low temperature growth of GaAs layers. Appl. Phys. Lett. 59, 3276. Hou, L., Shi, W., 2013. An LT-GaAs terahertz photoconductive antenna with high emission power, low noise, and good stability. IEEE Trans. Electron Devices. 60, 1619. Loukakos, P.A., Kalpouzos, C., Perakis, I.E., et al., 2002. The role of As precipitates on ultrafast electron trapping in low-temperature-grown GaAs and AlGaAs alloys. J. Appl. Phys. 91, 9863. Pastor, A.A., Serdobintsev, P.Yu., Chaldyshev, V.V., 2012. Experimental evaluation of the carrier lifetime in GaAs grown at low temperature. Semiconductors. 46, 619-621. Shen, Y.C., Upadhya, P.C., Beere, H.E., et al., 2004. Generation and detection of ultrabroadband terahertz radiation using photoconductive emitters and receivers. Appl. Phys. Lett. 85, 164. Wu, Q., Zhang, X.-C., 1996. Design and characterization of travelling-wave electroopticTHz sensors. IEEE J. Sel. Top. Quantum Electron. 3, 693.