Terahertz Pulse Emission from Semiconductor Heterostructures Caused by Ballistic Photocurrents

Abstract

Terahertz radiation pulses emitted after exciting semiconductor heterostructures by femtosecond optical pulses were used to determine the electron energy band offsets between different constituent materials. It has been shown that when the photon energy is sufficient enough to excite electrons in the narrower bandgap layer with an energy greater than the conduction band offset, the terahertz pulse changes its polarity. Theoretical analysis performed both analytically and by numerical Monte Carlo simulation has shown that the polarity inversion is caused by the electrons that are excited in the narrow bandgap layer with energies sufficient to surmount the band offset with the wide bandgap substrate. This effect is used to evaluate the energy band offsets in GaInAs/InP and GaInAsBi/InP heterostructures.

Generation of Terahertz Radiation under the Femtosecond Laser Excitation of a Multilayer Structure Based on a-Si:H/a-SiC:H/c-Si

“…Experimental results confirming the possibility of converting the energy of laser pulses to THz radiation in nonlinear crystals appeared in the mid-1980s [3,4]. Few-cycle THz pulses have already been generated in semiconductors, metals, dielectric crystals, and even in gases and liquids (see, e.g., [5] and references therein). The nature of such a THz generation is generally due to the excitation of a fast dipole or a short photocurrent burst in a material or a structure [6,7].…”

Semiconductor Characterization by Terahertz Excitation Spectroscopy

“…Quite informative TES spectra are also obtained by exciting the semiconductor heterojunction from the wide bandgap layer side. Such measurements are performed on GaInAs and GaInAsBi layers grown on InP substrates [ 85 ]. The results obtained from the GaInAs-InP heterostructure are illustrated in Figure 24 .…”

“… THz electric field pulses measured at two different optical wavelength beams impinging on GaInAs-InP heterostructure from the InP substrate side ( a ), and corresponding THz excitation spectrum (full red circles). Blue crosses show the Monte Carlo simulation results ( b ) [ 85 ]. …”

Возбуждение терагерцевого излучения в p-n-гетероструктурах на основе a-Si:H/c-Si

“…Генерация импульсов ТГц-излучения, содержащих несколько циклов электромагнитных колебаний, наблюдалась при фемтосекундном лазерном возбуждении многих полупроводников и полупроводниковых структур. В самом общем случае механизм такой ТГц-генерации обусловлен возбуждением в материале или структуре быстрого диполя или короткого всплеска фототока [5,6]. В дальнем поле амплитуда генерируемой таким образом ТГц-электромагнитной волны, E THz , пропорциональна ∂ 2 P ∂t 2 или ∂J ∂t , где P(t) и J(t) есть, соответственно, меняю-щиеся во времени дипольный момент или фототок, индуцированные фемтосекундным лазерным излучением.…”