We propose, fabricate, and evaluate strain-induced InGaAs/InAlAs superlattice (SL), which can efficiently radiate broadband terahertz (THz) waves. By means of optical pump-probe measurements, we demonstrate ultrashort photocarriers relaxation times of τ∼1.7ps without Be-doping of InGaAs photoconductive layers. We assume two dominant mechanisms to be responsible for a sharp reduction of τ in strained SL, which are photocarriers scattering at InGaAs/InAlAs heterointerface roughness and the decrease in the energy bandgap of InGaAs photoconductive layers due to the residual strain. The THz time-domain spectroscopic measurements reveal the rise in both emitted THz waveform and spectrum amplitudes with an increase of the residual strain in SL, in particular, at the low-frequency region. We refer this to the band structure engineering due to the residual strain in SL—since InGaAs photoconductive layers become compressively strained, this reduces the semiconductor’s energy bandgap, thus more photocarriers can contribute to the THz emission. The results might be of specific interest for the development of portable THz pulsed spectroscopic and imaging systems and other fundamental and applied aspects of the THz science and technology.
A detailed X-ray study of Zr rods, subjected to ECAP at 350oC by routes C and BC, was conducted by the new X-ray method of Generalized Pole Figures, combining texture measurement with registration of X-ray line profiles. The data analysis is based on conceptions of the texture formation theory, connecting features of grain reorientation with activated deformation mechanisms. A degree of reproduction of the same distinctive texture by successive ECAP passes with antecedent rotation of the rod reflects attendant structure changes in material.
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