Terahertz pulse generation from (111)-cut InSb and InAs crystals when illuminated by 155-μm femtosecond laser pulses

Abstract

Terahertz (THz) pulse generation from p-InAs, p-InSb, and n-InSb epitaxial layers are investigated using 1.55-μm wavelength femtosecond laser pulses for photoexcitation. The samples are of (111) crystallographic orientation resulting in anisotropic photoconductivity. Experiments have shown that THz generation in InAs is mainly due to anisotropic photocurrent in the surface electric field while a dominant mechanism in InSb is optical rectification. At high optical excitation fluencies, InSb is more efficient than p-InAs. In the presence of an external magnetic field, (111) InSb has exhibited promising viability as an alternative to the photoconductive antenna emitter in a THz time-domain-spectroscopy (THz-TDS) system.

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

“…Many cases are the fs laser illumination on the narrow bandgap semiconductors. 20,23,[25][26][27] The situation realizes the hot photocarrier injection with the energy far above the conduction bands. Thus the THz emission is explained by the quasi-ballistic high-energy-carrier transport.…”

“…Although, of course, the emission has the strong anisotropic properties depending on the effective mass, bandstructure, scattering time, etc. of the materials, 20 it is almost predictable that the THz emission due to the diffusion increases notably with increasing excess energy.…”

“…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.…”

Spatial chirping of a THz pulse during generation in InAs crystal

“…The generation of THz radiation using the Dember photoelectric effect leads to the generation of a one and a half cycle pulse [13]. In this work, we simulated the collimation of one and a half and multi-cycle pulses to observe the effects of spatial chirp and compare them.…”

Terahertz Pulse Emission from Semiconductor Heterostructures Caused by Ballistic Photocurrents

“…During the first few hundreds of femtoseconds, when the dipole is developing, the photoexcited electrons in narrow-gap A3B5 semiconductors are moving ballistically [9] over the distances reaching several hundred nanometers [10]. Due to the electrons not being scattered during this stage, the initial optical orientation of their momenta [11] is conserved and it is also reflected in the azimuthal angle dependences of THz emission for certain photoexcited crystal planes [12,13].…”