Spectral dependencies of terahertz emission from femtosecond laser excited surfaces of germanium crystals

Norkus, Ričardas; Nevinskas, Ignas; Krotkus, A.

doi:10.1063/1.5128186

Cited by 6 publications

(14 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…18 The ultrafast optical response in the wide bandgap semiconductors is still an unexplored area where it is worth applying TES. However, the emission mechanism includes complex carrier dynamics [19][20][21][22] , such as anisotropic optical responses, because of which we might have to evaluate them for each case by means of simulations such as Monte-Carlo method. For the semiconductor industrial applications, it is desirable to have a simplified modeling and capture instinct carrier dynamics.…”

Section: Introductionmentioning

confidence: 99%

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Tonouchi

2020

Journal of Applied Physics

View full text Add to dashboard Cite

We derive simple formulas to explain terahertz (THz) emission from semiconductor surfaces excited by a femtosecond (fs) laser. Femtosecond optical pulses with energies larger than the bandgap create photocarriers which travel and generate THz radiation, according to the time derivative of the photocurrent. By assuming that only electrons traveling in an ultrafast time scale, less than a few hundred fs, contribute to THz radiation, one can obtain simple expressions for the emission originating from the photocarrier drift accelerated with a built-in field or from the photocarrier diffusion. The emission amplitude of the former is in proportion with electron mobility, the Schottky-Barrier height, and the laser intensity and one of the latter with the laser intensity and diffusion coefficient squared. We also discuss the formula for emission from metal-insulator-semiconductor structures. The derived expressions are useful in understanding the THz emission properties observed by a laser THz emission microscope (LTEM), bringing LTEM into real applications in the field of semiconductor research and development.

show abstract

Section: Introductionmentioning

confidence: 99%

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Tonouchi

2020

Journal of Applied Physics

View full text Add to dashboard Cite

show abstract

“…The dependence of generated THz pulse amplitude from unintentionally doped n-Ge crystal with

cm resistivity and

electron density on the exciting photon energy is plotted in Figure 11 a. The dependencies on the azimuthal angle, measured by illuminating the (111) crystal plane with a femtosecond laser beam of different wavelengths, perpendicular to the surface, are shown in Figure 11 b [ 39 ]. As could be expected, a more pronounced THz emission is observed when the photon energy reaches the direct bandgap at

points.…”

Section: Other Semiconductor Crystalsmentioning

confidence: 99%

“…Microscopically, the presence of these effects in semiconductors is explained by the lateral surface photocurrents appearing due to an optical alignment and anisotropic electron energy dispersion law. It is suggested in [ 39 ] that the clear azimuthal angle dependencies are most probably caused by the warping of the heavy hole valence band [ 17 ] rather than the non-sphericity of the conduction band.…”

Section: Other Semiconductor Crystalsmentioning

confidence: 99%

See 1 more Smart Citation

Semiconductor Characterization by Terahertz Excitation Spectroscopy

2023

Self Cite

View full text Add to dashboard Cite

Surfaces of semiconducting materials excited by femtosecond laser pulses emit electromagnetic waves in the terahertz (THz) frequency range, which by definition is the 0.1–10 THz region. The nature of terahertz radiation pulses is, in the majority of cases, explained by the appearance of ultrafast photocurrents. THz pulse duration is comparable with the photocarrier momentum relaxation time, thus such hot-carrier effects as the velocity overshoot, ballistic carrier motion, and optical carrier alignment must be taken into consideration when explaining experimental observations of terahertz emission. Novel commercially available tools such as optical parametric amplifiers that are capable of generating femtosecond optical pulses within a wide spectral range allow performing new unique experiments. By exciting semiconductor surfaces with various photon energies, it is possible to look into the ultrafast processes taking place at different electron energy levels of the investigated materials. The experimental technique known as the THz excitation spectroscopy (TES) can be used as a contactless method to study the band structure and investigate the ultrafast processes of various technologically important materials. A recent decade of investigations with the THz excitation spectroscopy method is reviewed in this article. TES experiments performed on the common bulk A3B5 compounds such as the wide-gap GaAs, and narrow-gap InAs and InSb, as well as Ge, Te, GaSe and other bulk semiconductors are reviewed. Finally, the results obtained by this non-contact technique on low-dimensional materials such as ultrathin mono-elemental Bi films, InAs, InGaAs, and GaAs nanowires are also presented.

show abstract

“…Therefore, there is an increasing demand for high-efficiency THz emission sources and high-sensitivity THz wave detectors. Semiconductor materials, such as layered centrosymmetric 2H-MoS 2 (TMDs), InAs, graphene, and Ge crystals, feature high carrier mobility, wide band range, high current on/off and other photoelectric properties, and have been used as sources of electromagnetic radiation in the THz range [7][8][9][10][11]. Additionally, THz emission strength and efficiency can be further improved by constructing semiconductor/metal Schottky interfaces.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Terahertz Radiation by Surface Plasmons Based on CdTe Thin Films

Kong

Huang

et al. 2022

Nanomaterials

View full text Add to dashboard Cite

Terahertz (THz) time-domain spectroscopy (TDS) is a powerful tool used to characterize the surface/interface of materials, and semiconductor/metal interfaces can generate THz emission through ultrafast optical excitation, which can be further improved through the optical excitation of surface plasmons. Here, we assembled cadmium telluride (CdTe) on an AuAg alloy (Au25Ag75, wt.%) substrate and obtained five times stronger THz emission compared with silicon substrate, and found that the enhancement can be tuned by controlling the thickness of the semiconductor materials and plasmonic metal substrates. We believe that our results not only promote the development of THz emission enhancement, but also provide a straightforward way of producing small, thin, and more efficient terahertz photonic devices.

show abstract

Spectral dependencies of terahertz emission from femtosecond laser excited surfaces of germanium crystals

Cited by 6 publications

References 24 publications

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Semiconductor Characterization by Terahertz Excitation Spectroscopy

Enhancement of Terahertz Radiation by Surface Plasmons Based on CdTe Thin Films

Contact Info

Product

Resources

About