[Show abstract][Hide abstract] ABSTRACT: The “optical pump-terahertz probe” technique is used to investigate the spectral dependence of the anisotropic picosecond photoconductivity in an InGaAs cubic semiconductor excited by femtosecond laser pulses. It is shown that the anisotropy of the photoconductivity, which is caused by the alignment of the momenta of photoexcited charge carriers and by the energy dependence of the carrier mobility, depends nonmonotonically on the photon energy of the optical pump radiation and attains a maximum when the energy of pump photons is in the vicinity of the threshold for the onset of electron transitions to the subsidiary valleys in the conduction band.
[Show abstract][Hide abstract] ABSTRACT: Transient photoconductivity in cubic semiconductors InGaAs and InAs excited by a femtosecond laser pulse in the presence of a uniform dc electric field has been studied with the use of the Monte Carlo simulation by taking into account optical alignment of photoexcited electrons over their momenta. Simulations show that due to the optical alignment effect and energy dependence of the electron mobility, the transient photoconductivity in cubic semiconductors becomes anisotropic during the first few picoseconds after optical excitation. The magnitude of this anisotropy reaches its peak when the excess energy of the optically excited electrons approaches the threshold for the intervalley transfer. It has also been found that when the electrons are excited near the threshold energy for the intervalley transfer, the component of the transient photocurrent directed along the dc field for a short time after the end of the femtosecond optical pulse can become negative. The anisotropy of the transient photoconductivity has been investigated experimentally on (001) InGaAs sample by the optical pump - terahertz-probe technique. Optically induced changes in terahertz pulse amplitude were found to be dependent on the direction of terahertz field relative to the polarization of the optical pump pulse and to the crystallographic axes of the semiconductor. Experimental data have been explained in terms of the transient anisotropic photoconductivity and correlate with the results of the Monte Carlo simulation.
Full-text · Article · Jan 2014 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Terahertz emission from the surfaces of narrow-gap semiconductors excited by femtosecond laser pulses was described in terms of a transient interband photoconductivity. It has been found that the nonparabolicity of the electron dispersion law as well as the optical alignment of the photoexcited carrier momenta result in anisotropic photocurrent with a component perpendicular to the surface dc electric field even in semiconductors with a cubic symmetry. This lateral transient photocurrent component is the strongest during the first few hundreds of femtoseconds after the photoexcitation and causes the emission of terahertz radiation pulses with an amplitude dependent on the angle between the optical field and the crystallographic axes. In the case of InAs the contribution of this component explains experimental results of both the azimuthal anisotropy of the emitted terahertz pulse amplitude and its dependence on the exciting photon energy.
Full-text · Article · Oct 2012 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: The terahertz (THz) power radiated by the femtosecond laser excited semiconductor surfaces was measured by the Golay cell. Intrinsic InSb crystals as well as n- and p-type InAs were investigated by using three different wavelength, 780, 1030, 1550 nm, femtosecond lasers. It has been shown that p-type InAs crystal is the most efficient THz emitter for all three laser wavelengths with a nearly constant optical-to-THz power conversion efficiency of approximately 10<sup>-6</sup>.
Full-text · Article · Nov 2011 · Electronics Letters