Abstract
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.
Highlights
Terahertz (THz) time-domain spectroscopy has been used to investigate molecular motions in gaseous or liquid states and carrier dynamics in various materials, such as, semiconductors, dielectrics, etc.[1,2,3,4] THz radiation enables direct observation of low-energy modes of materials, such as, molecular rotations, phonons, polaritons, and charge and spin waves by resonance excitation.[5]
Of THz radiation generated from a transient current in an illuminated semiconductor is expressed as: ETHz (t )
The waveforms normalized to the peak amplitudes imply that the decay of N(t) in the sample is faster than that of N(t) in the semi insulating (SI)-GaAs wafer, while their increase characteristics of N(t) are approximately equal (Figure S1, supplementary material, SI)
Summary
Terahertz (THz) time-domain spectroscopy has been used to investigate molecular motions in gaseous or liquid states and carrier dynamics in various materials, such as, semiconductors, dielectrics, etc.[1,2,3,4] THz radiation enables direct observation of low-energy modes of materials, such as, molecular rotations, phonons, polaritons, and charge and spin waves by resonance excitation.[5]. Charged states at the surface of a semiconductor are directly related with the radiated THz waveform.[6,7,8,9]. Semiconductors illuminated by a femtosecond laser beam can emit THz radiation. Introduction of nanostructures on a Ge wafer can enhance the amplitude of THz radiation without changing the spectral bandwidth.[10] Disordered nanostructures on a GaAs wafer can broaden the spectral bandwidth.[11]. The properties of THz radiation emitted from GaAs microstructures with sizes of a few micrometers are worth studying as micrograins and rich defect states of the microstructures can increase the transient current and lead to a fast current decay. The properties of THz radiation from illuminated GaAs microstructures on a Si substrate are reported. GaAs microstructures on a Si substrate can be utilized as an efficient THz radiation source
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