Intense THz emission in high quality MBE-grown GaAs film with a thin n-doped buffer (original) (raw)
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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.
Applied Physics Letters, 2008
We have investigated the emission of the terahertz electromagnetic wave from an undoped GaAs ͑200 nm͒ / n-type GaAs ͑3 m͒ epitaxial layer structure ͑i-GaAs/ n-GaAs structure͒, where the doping concentration of the n-GaAs layer is 3 ϫ 10 18 cm −3. It is found that the first-burst amplitude of terahertz wave of the i-GaAs/ n-GaAs sample is remarkably larger than that of a n-GaAs crystal, which means that the i-GaAs layer enhances the terahertz emission intensity. The first-burst amplitude of the i-GaAs/ n-GaAs sample, by tuning the pump-beam energy to the higher energy side, exceeds that of an i-InAs crystal that is known as one of the most intense terahertz emitters. We, therefore, conclude that the i-GaAs/ n-GaAs structure is useful to obtain intense terahertz emission.
Enhanced Optically–Excited THz Wave Emission by GaAs Coated with a Rough ITO Thin Film
Coatings
In this study, we report enhancement of terahertz (THz) radiation with indium-tin-oxide (ITO) thin-film deposited on semi-insulating gallium arsenide substrate (SI-GaAs). The amplitude of THz emission from both ITO/SI-GaAs and bare SI-GaAs substrate as a function of optical pump (i) incident angle, (ii) polarization angle, and (iii) power were investigated. The enhancement of peak amplitude of a THz pulse transmitted through the ITO/SI-GaAs sample in comparison to bare SI-GaAs substrate varied from 100% to 0% when the pump incidence angle changed from 0° to 50°. The maximum enhancement ratio of peak amplitude for a coated sample relative to the bare substrate is approximately up to 2.5 times at the minimum pump intensity of 3.6 TW/m2 and gradually decreased to one at the maximum pump intensity of 20 TW/m2. From outcomes of these studies, together with data on surface and material characterization of the samples, we show that THz emission originates from the ITO/GaAs interfaces. Furt...
Terahertz radiation from delta-doped GaAs
Applied Physics Letters, 1994
Terahertz pulse emission from four different delta-doped molecular beam epitaxially grown GaAs samples is studied. We observe a decrease of the emitted THz pulse amplitude as the distance of the delta-doped layer from the surface is increased, and a change in polarity of the THz pulses as compared to bulk n-type doped GaAs reference samples. The electric fields in the region of the doping layer are investigated by photoreflectance spectroscopy. A careful analysis of Franz–Keldysh oscillations observed in the photoreflectance spectra provides information about the built-in fields on both sides of the delta-doped layer.
Investigation of the terahertz emission characteristics of MBE-grown GaAs-based nanostructures
Optical Materials, 2010
We report experimental work on the terahertz emission characteristics of InAs/GaAs quantum dot (QD) structures and GaAs/AlGaAs modulation-doped heterojunctions (MDH's), excited by femtosecond laser. Results showed that the terahertz emission from MDH's can provide information on the GaAs/AlGaAs interface quality while the QD structures have the potential for being intense terahertz emitters; rivaling the emission intensity of p-type bulk InAs.
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.
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 Applied Physics, 2005
The optical properties of p-type Al x Ga 1−x As ͑x = 0, 0.01, and 0.16͒ epitaxial films with different beryllium and carbon doping concentrations ͑10 18-10 19 cm −3 ͒ were investigated by far-infrared reflectance spectroscopy in the 1.5-15-THz frequency range. The dielectric response functions of the film samples were expressed using the classical Lorentz-Drude model. Optical properties were obtained using a three-phase model ͑air/film/substrate͒ which agrees with the experimental reflectance spectral data. The effects of doping concentrations on the optical constants were studied in detail. The results indicate that the refractive index increases with the doping concentration in the low-frequency region ͑ഛ5 THz͒ where the free-carrier absorption plays an important role in the optical response. However, the extinction coefficient increases with the doping concentration in the entire frequency region. This indicates that the absorption coefficient increases with the doping concentration. The calculated plasma frequencies agree with the values obtained from the measured doping concentrations. The free-carrier scattering time is ϳ1.39ϫ 10 −14 s. The longitudinal-optical phonon plasmon coupled modes of the Al x Ga 1−x As films are presented. The upper coupled mode increases with the doping concentration and shows a transition from phononlike to plasmonlike behavior. A sublinear relationship between the absorption coefficient and the doping concentration for p-type Al x Ga 1−x As epitaxial films was obtained at a frequency of 3.75 THz ͑80 m͒. These results can be used to design and improve the performance of terahertz detectors.