Enhanced Optically–Excited THz Wave Emission by GaAs Coated with a Rough ITO Thin Film (original) (raw)
Related papers
Influence of Substrate Material on Radiation Characteristics of THz Photoconductive Emitters
International Journal of Antennas and Propagation, 2015
We present in this paper spectral and spatial characteristics of terahertz emission from standard dipole antenna structures used as emitters depending on the substrate material. All antenna structures were lithographically fabricated on low-temperature (LT) grown, few-micrometers-thick gallium arsenide (GaAs) layers. To investigate the effect of the substrate material on the radiation pattern of terahertz beams, either semi-insulating gallium arsenide or high-resistivity silicon substrate wafers have been used. As detector a standard 40 µm long dipole antenna on a semi-insulating GaAs substrate with a low-temperature grown gallium arsenide layer on it has been employed; this configuration allows for broadband detection and is still efficient enough for the characterization purpose. Strong dependence of the radiation pattern on the substrate used for the terahertz source is demonstrated. The measured patterns and differences between the two cases of substrates are well explained by m...
Excitation wavelength dependence of terahertz emission from semiconductor surface
Applied Physics Letters, 2006
The authors have measured terahertz radiation from InSb, InAs, and InGaAs excited by femtosecond optical pulses at wavelengths of 1560, 1050, and 780 nm. The amplitude of the terahertz field strongly depends on the pump wavelengths. Among the materials, the InSb emitter shows the largest terahertz emission amplitude at high power 1560 nm excitation, whereas 780 nm excitation provides the weakest. With increasing photon energy, the increase in emission amplitude from InAs is less as compared to that from InGaAs. The decrease from InSb and InAs originates in low mobilities of L or X valley carriers generated by intervalley scatterings.
Intense THz emission in high quality MBE-grown GaAs film with a thin n-doped buffer
Optical Materials Express, 2018
Intense terahertz (THz) emission in high quality GaAs film upon ultrafast excitation is demonstrated. Results showed that high quality GaAs grown by molecular beam epitaxy with a thin n-doped buffer can rival existing intense bare semiconductor THz surface emitters. The incorporation of a 0.2 µm n-GaAs buffer proved effective in enhancing the THz emission of GaAs by 281% and 295% in reflection and transmission THz time-domain excitation geometries, respectively. The GaAs film was of high crystallinity with or without the n-doped buffer layer as confirmed from X-ray diffraction and Raman scattering. The similar crystalline quality of the two samples was further exemplified by their comparable built-in field strength as measured by photoreflectance spectroscopy. The distinguishable difference in GaAs with and without the doped buffer was observed via low temperature photoluminescence (PL) spectroscopy. The GaAs film with the n-doped buffer exhibited intense GaAs PL while the GaAs film without the n-doped buffer exhibited prominent carbon impurity-related PL. THz enhancement was inferred to be due to the decrease in shallow defects in GaAs with n-doped buffer.
Strong emission of THz radiation from GaAs microstructures on Si
AIP Advances
Remarkably strong emission of terahertz radiation from illuminated GaAs microstructures on a Si substrate is reported. The peak-to-peak amplitude of terahertz radiation from the sample is 9 times larger than that of THz radiation from a semi-insulating GaAs wafer. The spectral width of the sample is larger than that of a semi-insulating GaAs wafer; in particular, the spectral amplitude increases at higher frequencies. The presented GaAs microstructures on a Si substrate can be suitable for practical and efficient THz sources required in various THz applications.
Thickness dependence of terahertz emission in InAs and its application to transmissive source
2011
In situ study of the growth properties of Ni-rare earth silicides for interlayer and alloy systems on Si(100) J. Appl. Phys. 111, 043511 (2012) Surface diffusion and layer morphology of ((112)) GaN grown by metal-organic vapor phase epitaxy J. Appl. Phys. 111, 033526 Search for a small hole in a cavity wall by intermittent bulk and surface diffusion J. Chem. Phys. 136, 054115 Simultaneous step meandering and bunching instabilities controlled by Ehrlich-Schwoebel barrier and elastic interaction Appl. Phys. Lett. 99, 263106 (2011) Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy Abstract. Terahertz(THz) radiation properties from InAs layers grown on GaAs has been studied as a function of thickness ranging from 0. ȝm to 1.74 ȝm. The amplitude showed a monotonic increment up to 0.9 ȝm, followed by a decrement at 1.74 ȝm. The phase-shift between 0.07 and 0.37 ȝm was also observed, which was possibly associated with the transition of the major generation mechanism from drift to diffusion with increasing thickness.
Optical Materials, 2019
Enhanced terahertz (THz) radiation was generated from a gallium arsenide thin film integrated on top of porous silicon distributed Bragg reflector (GaAs/PSi DBR). The film's thickness was designed to be less than the penetration depth of the 800 nm excitation source, while the PSi DBR was centered at the laser wavelength to reflect the transmitted photons at the film-substrate interface. Reflection-geometry THz time-domain spectroscopy measurement revealed enhancement in THz peak to peak amplitude by 1.67 and 5.7 times as compared to the same thickness of GaAs on silicon (GaAs/Si) and bulk semi-insulating (SI) GaAs, respectively. In comparison with the bulk SI-GaAs, both thin film samples showed an order of magnitude improvement in the THz output power. The excitation-wavelength study also revealed a maximum increase near the design wavelength. The enhancement was attributed to the high reflectivity at the film-substrate interface and optical cavity effect in GaAs. These factors contributed to an effective optical confinement within the film's THz generation region.
Diffusion and drift in terahertz emission at GaAs surfaces
We study terahertz ͑THz͒ emission from GaAs as a function of photon energy and electric field. THz radiation arises from transport of photogenerated charge in an electric field and by hot carrier diffusion ͑the photo-Dember effect͒. These mechanisms can be separated by experiments in which either the electric field or the kinetic energy of the carriers is varied. For electric fields E ϳ4 kV/cm, we find that the electric field controls THz emission for carrier temperatures k B T C р0.1 eV, while hot-carrier diffusion dominates for k B T C Ϸ1 eV. Both mechanisms contribute at intermediate fields and carrier temperatures. Our results are consistent with estimates of the relative magnitudes of these two effects.
Journal of Materials Science: Materials in Electronics, 2021
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 = 320 °C, 520 °C and 630 °C). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at Ts = 600 °C. 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 = 320 °C, 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...
Surface effect of n-GaAs cap on the THz emission in LT-GaAs
Journal of Materials Science: Materials in Electronics, 2018
The deposition of n-GaAs cap on low-temperature GaAs (LT-GaAs) improved the THz emission of LT-GaAs grown at a much lower temperature (< 300 • C), where the defect density is high, without compromising the spectral bandwidth and carrier lifetimes necessary for ultrafast THz detection. The LT-GaAs grown at 220 and 270 • C showed a 192 and 10% enhancement THz emission peak-to-peak intensity, respectively, while the sample grown at 310 • C showed a 49% reduction. The n-GaAs cap reduced the As-related defects density in the LT-GaAs resulting to improved THz emission. The THz emission from the sample grown at 310 • C with already low defect density suffered possibly due to the free carrier absorption by the n-GaAs cap. The results are relevant in future material design of LT-GaAs based photoconductive antenna.