Strong emission of terahertz radiation from nanostructured Ge surfaces

Kang, Chul; Leem, Jung Woo; Maeng, Inhee; Kim, Tae Heon; Lee, Jong Seok; Yu, Jae Su; Kee, Chul‐Sik

doi:10.1063/1.4923372

Cited by 12 publications

(12 citation statements)

References 18 publications

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“…Nevertheless, high crystallinity is not an exclusive requisite for intense THz emission. Semiconductors with surface structures have been shown to emit enhanced THz radiation [13,14]. Recently, GaAs microstructures on Si has been shown to exhibit intense THz radiation in comparison with semi-insulating (SI)-GaAs [14].…”

Section: Introductionmentioning

confidence: 99%

Terahertz Emission Increase in GaAs Films Exhibiting Structural Defects Grown on Si (100) Substrates Using a Two-Layered LTG-GaAs Buffer System

Gonzales

Prieto

Catindig

et al. 2021

Preprint

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Terahertz (THz) emission increase is observed for GaAs thin films that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (Ts = 320ºC, 520ºC and 630ºC). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at Ts = 600ºC. Reflection high energy electron diffraction confirms the layer-by-layer growth mode of the GaAs on Si. X-ray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz time-domain spectroscopy is performed in reflection and transmission excitation geometries. At Ts = 320ºC, the low crystallinity of GaAs on Si makes it an inferior THz emitter in reflection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher Ts, the GaAs on Si thin films emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identified from scanning electron microscopy and Raman spectroscopy. An intense THz emission in reflection and transmission excitation geometries is observed for the GaAs on Si grown at Ts = 520ºC, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most efficient in both excitation geometries. The results are significant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices.

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Section: Introductionmentioning

confidence: 99%

Terahertz Emission Increase in GaAs Films Exhibiting Structural Defects Grown on Si (100) Substrates Using a Two-Layered LTG-GaAs Buffer System

Gonzales

Prieto

Catindig

et al. 2021

Preprint

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show abstract

Section: Introductionmentioning

confidence: 99%

Terahertz emission increase in GaAs films exhibiting structural defects grown on Si (100) substrates using a two-layered LTG-GaAs buffer system

Gonzales

Prieto

Catindig

et al. 2021

J Mater Sci: Mater Electron

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Terahertz (THz) emission increase is observed for GaAs thin lms that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (T s = 320ºC, 520ºC and 630ºC). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at T s = 600ºC.Re ection high energy electron diffraction con rms the layer-by-layer growth mode of the GaAs on Si. Xray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz timedomain spectroscopy is performed in re ection and transmission excitation geometries. At T s = 320ºC, the low crystallinity of GaAs on Si makes it an inferior THz emitter in re ection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher T s , the GaAs on Si thin lms emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identi ed from scanning electron microscopy and Raman spectroscopy. An intense THz emission in re ection and transmission excitation geometries is observed for the GaAs on Si grown at T s = 520ºC, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most e cient in both excitation geometries. The results are signi cant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices. Relevance SummaryDemonstration of GaAs integration on exact n-type undoped Si(100) by MBE using a two-layer LTG-GaAs buffer system. The buffer system allows for a controlled growth of relatively high-quality GaAs layers at different substrate temperatures as con rmed by in-situ RHEED, SEM, XRD diffraction and Raman spectroscopy. Utilization of Si substrates, which has a lower absorption in the THz region, to establish a GaAsbased THz emitter that is more effective in both re ection and transmission excitation geometries.The GaAs on Si material system will constitute a cost-effective THz photoconductive antenna device and likewise provide an improved refractive index matching with a Si lens mount.Con rmation of THz emission enhancement in GaAs on Si heterostructure, which is not solely dependent on high crystallinity but also on the presence of structural defects such as APBs.Validation of the reduced THz absorption losses in GaAs on Si structures advantageous for THz measurements in transmission excitation geometry.Establishment of GaAs on Si as a more effective material system even with the presence of structural defects over LTG-GaAs homostructure in the generation of THz radiation in both re ection and transmission excitation geometries.

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“…[ 12 ] These reports suggest that the periodic arrays of nanostructures play an essential role for improved light‐matter interactions such as enhanced surface plasmon based sensing and improved terahertz emission. [ 3,4,13 ]…”

Section: Introductionmentioning

confidence: 99%

“…Controlled and periodic germanium nanostructures exhibit significant applications in lasing, [ 1,2 ] infrared surface plasmon based molecular sensing, [ 3,4 ] surface‐enhanced infrared absorption spectroscopy, [ 5,6 ] photovoltaic, [ 7,8 ] as photodetectors in optoelectronics, [ 9,10 ] enhanced light trapping, [ 3,11 ] and terahertz radiation (THz radiation) emission. [ 12–14 ] Partially amorphized Ge quantum dots encapsulated in the silicon matrix are proven to show an improved lasing action making them potentially useful for application in silicon integrated technology. [ 1,2 ] Enhanced molecular sensing capabilities have been demonstrated by plasmon‐enhanced infrared absorption due to an array of germanium nanostructures.…”

Section: Introductionmentioning

confidence: 99%

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Tailoring Surface Self‐Organization for Nanoscale Polygonal Morphology on Germanium

et al. 2021

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radiation (THz radiation) emission. [12][13][14] Partially amorphized Ge quantum dots encapsulated in the silicon matrix are proven to show an improved lasing action making them potentially useful for application in silicon integrated technology. [1,2] Enhanced molecular sensing capabilities have been demonstrated by plasmonenhanced infrared absorption due to an array of germanium nanostructures. [3,4] Arrays of GeSi nanostructures on silicon substrate showed an enhancement in the photo-voltage, showing promise for solar cell applications. [10] Surprisingly, germanium being an indirect bandgap semiconductor, periodic arrays of germanium nanostructures gave rise to THz radiation emission with comparable amplitude to the direct bandgap semiconductor n-GaAs (n-type GaAs). [13] Germanium nanostructures show threefold to fivefold increased amplitude of THz radiation emission as compared to the baregermanium surface. Local surface charge collection due to the high surface area is attributed to the enhanced THz emission from the Ge nanostructures. [12] These reports suggest that the periodic arrays of nanostructures play an essential role for improved light-matter interactions such as enhanced surface plasmon based sensing and improved terahertz emission. [3,4,13] The evolution of polygonal-shaped nanoholes on the (100) surface of germanium, aided by focused ion beam induced self-organization, is presented. The energetic beam of ions creates a viscous phase which, at a thermodynamical minimum, leads to surface self-organization. A directed viscous-flow along the predefined nanoholes provides well-ordered polygonal nanostructures, ranging from triangles to hexagons and octagons, as desired. The amorphization exhibiting a confined viscous-flow at the walls of nanoholes is attributed to the localized melting zones induced by sitespecific thermal spikes during ion irradiation, as revealed by microscopy and molecular dynamics studies. This leads to a local self-organization in the vicinity of each circular nanohole via a viscous-fingering process at the nanoscale. Such controlled self-organization, with the help of a predefined scanning grid, transforms the circular holes into the desired polygonal shape. The present morphology manipulation promises to surmount the barriers concerning the size reduction efforts in the field of nanofabrication.

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Strong emission of terahertz radiation from nanostructured Ge surfaces

Cited by 12 publications

References 18 publications

Terahertz Emission Increase in GaAs Films Exhibiting Structural Defects Grown on Si (100) Substrates Using a Two-Layered LTG-GaAs Buffer System

Terahertz Emission Increase in GaAs Films Exhibiting Structural Defects Grown on Si (100) Substrates Using a Two-Layered LTG-GaAs Buffer System

Terahertz emission increase in GaAs films exhibiting structural defects grown on Si (100) substrates using a two-layered LTG-GaAs buffer system

Tailoring Surface Self‐Organization for Nanoscale Polygonal Morphology on Germanium

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