Terahertz emission from a bulk GaSe crystal excited by above bandgap photons

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

doi:10.1063/5.0027944

Cited by 7 publications

(7 citation statements)

References 36 publications

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“…THz pulses emitted from GaSe excited by laser pulses with photon energies higher than the energy bandgap were first measured in ref. [ 56 ]. A characteristic feature of this material with a trigonal crystal structure is the pronounced dependence of the signal on the azimuthal angle ( Figure 15 ) and different, mutually independent spectral dependencies of the THz signal components dependent and independent of this angle.…”

Section: Other Semiconductor Crystalsmentioning

confidence: 99%

“…All studies in the work of Norkus et al [ 56 ] were performed using 50

m thick GaSe samples, where the influence of the nonlinear optical response of bound electrons was minimal. As for the azimuthal angle

-independent component, it is logical to assume that it is due to the dynamic photocurrent flowing from the surface to the bulk.…”

Section: Other Semiconductor Crystalsmentioning

confidence: 99%

“…The GaSe sample is illuminated at a 30angle to surface normal. Reproduced from [ 56 ], with the permission of AIP Publishing.…”

Section: Figurementioning

confidence: 99%

“… TES spectrum of GaSe azimuthal angle dependent THz pulse part ( a ), and the azimuthal angle independent part when illuminated by S- (red squares) and P-polarized (blue triangles) optical beams ( b ). Reproduced from [ 56 ], with the permission of AIP Publishing. …”

Section: Figurementioning

confidence: 99%

“…The first peak dominated in thick GaSe layers comparable to the coherence length (~1 mm); in layers thinner than 0.1 mm, the second peak prevailed. Reproduced from [56], with the permission of AIP Publishing.…”

Section: Gallium Selenidementioning

confidence: 99%

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Semiconductor Characterization by Terahertz Excitation Spectroscopy

2023

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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.

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Section: Other Semiconductor Crystalsmentioning

confidence: 99%

“…All studies in the work of Norkus et al [ 56 ] were performed using 50

m thick GaSe samples, where the influence of the nonlinear optical response of bound electrons was minimal. As for the azimuthal angle

-independent component, it is logical to assume that it is due to the dynamic photocurrent flowing from the surface to the bulk.…”

Section: Other Semiconductor Crystalsmentioning

confidence: 99%

“…The GaSe sample is illuminated at a 30angle to surface normal. Reproduced from [ 56 ], with the permission of AIP Publishing.…”

Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Section: Gallium Selenidementioning

confidence: 99%

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Semiconductor Characterization by Terahertz Excitation Spectroscopy

2023

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Direct bandgap dependence of bismuth films on their thickness

Nevinskas

Stanionytė

Devenson

et al. 2022

Journal of Applied Physics

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Thin bismuth films of various thicknesses between 5 and 32 nm grown by molecular beam epitaxy on Si (111) substrates were investigated. The samples were characterized by the x-ray diffraction method, which allowed us to identify two types of Bi crystallographic structures—[Formula: see text] and [Formula: see text] bismuth. Terahertz radiation pulses emitted from the samples after their illumination by femtosecond optical pulses with different wavelengths were characterized. The main THz emission features were similar for both types of Bi layers. Due to 2D confinement, the electron energy band structure depends on the thickness. With the terahertz excitation spectroscopy method, direct bandgaps were determined to be in the range from 0.25 to 0.5 eV—much greater than the indirect bandgaps of the layers. A simple model was used to describe the nature of THz emission from these films, which is the cause of uncompensated lateral photocurrents occurring because of the diffusive electron scattering at the Bi/Si interface.

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THz generation in GaSe crystals pumped with laser photon energy below and around the bandgap

Zhai

Hérault

Garet

et al. 2023

Applied Physics Letters

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We study optical rectification in GaSe by performing THz generation with femtosecond laser pulses whose wavelength is tuned from below to above the GaSe bandgap. As expected from a theory, we observed a first THz emission peak at 1.77 eV, where phase matching is realized. A second THz emission peak was recorded, when the pump photon energy reaches the crystal bandgap (2.205 eV). This can be attributed to a resonance of the GaSe nonlinearity. In crystals thinner than the coherence length, the bandgap peak is stronger than the phase-matched one.

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Terahertz emission from a bulk GaSe crystal excited by above bandgap photons

Cited by 7 publications

References 36 publications

Semiconductor Characterization by Terahertz Excitation Spectroscopy

Semiconductor Characterization by Terahertz Excitation Spectroscopy

Direct bandgap dependence of bismuth films on their thickness

THz generation in GaSe crystals pumped with laser photon energy below and around the bandgap

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