Influence of Substrate Material on Radiation Characteristics of THz Photoconductive Emitters

Abstract

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 means of classical diffraction.

Beam Profiling of a Commercial Lens-Assisted Terahertz Time Domain Spectrometer

“…2(b) and 4(c) (measured in the central plane and the plane 4 mm from the detector) exhibit interference fringes. Given the recorded temporal window of 52 ps, these fringes are attributed to the refractive index step between the silicon lens and InP substrate of the emitter [13], [18], [20], as confirmed by our CST Microwave Studio® full-wave simulations. It should be noted that these fringes do not appear in the pinholeonly scan images ( Fig.…”

Co2FeAl Full Heusler Compound Based Spintronic Terahertz Emitter

“…This effect of the ringing can be seen in several publications displaying the THz signal in the time and frequency domains. [25][26][27][28] The peak-to-peak amplitude of the THz signal (E THz ) in time-domain is measured for all CFA/Pt STEs and used as the dependent variable in Equation ( 3) with the CFA thickness as an independent variable. The explanation of Equation ( 3) is given in the following section.…”

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

“…Although previous works have shown that both the surface [14] and interface eld [1,2] play a signi cant role in the enhancement of THz radiation in GaAs on Si, their growth schematics are not intended for THz PCA device fabrication. The device fabrication of PCA involves the deposition of metal contacts on a relatively smooth (specular) and thick (~ 2 µm) semiconductor epilayer [3,15,16]. These particularities can be challenging with the deposition of GaAs on Si.…”

“…The method is a combination of the two-step growth and the concept of utilizing an intermediate layer that are conventional in GaAs on Si processes [5][6][7][9][10][11][12]. An LTG-GaAs (T s < 450ºC [21,22]) is a common material for the generation and detection of THz radiation by ultrafast switching of PCA [3,15,16]. The growth method is intended not to deviate far from the standard LTG-GaAs on SI-GaAs processes for direct comparison while establishing a ~ 2 µm-GaAs epilayer without surface cracks, pinholes and has minimized surface roughness.…”