Exciton Contribution to the Photoinduced Giga- and Terahertz Permittivity of Semiconductors

• Published in: Journal of communications technology & electronics Vol. 67; no. 12; pp. 1436 - 1442
• Main Authors: Butylkin, V. S., Fisher, P. S., Kraftmakher, G. A., Kazantsev, Yu. N., Kalenov, D. S., Mal’tsev, V. P., Parkhomenko, M. P.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2022; Springer; Springer Nature B.V
• Subjects: Communications Engineering; Engineering; Excitons; Fiber optics; Frequency ranges; Irradiation; Networks; Permittivity; Radio Phenomena in Solids and Plasma; Semiconductors; Terahertz frequencies; Transmittance; Waveguides
• ISSN: 1064-2269; 1555-6557
• DOI: 10.1134/S1064226922120038

A unified approach based on the application of the exciton density matrix is used to study photoinduced permittivity ε of semiconductors in the spectral interval combining gigahertz (GHz) and terahertz (THz) frequency ranges. A significant difference in the behavior of ε in the GHz and THz ranges is revealed. It is shown that an increase in power P λ of optical irradiation leads to a decrease in Reε at frequencies ω > Δω ex (THz range, Drude-like behavior) and an increase at ω < Δω ex (GHz range, non-Drude-like behavior) (Δω ex is the frequency interval of transitions involving the most populated exciton levels). The growth of Imε with increasing P λ reaches maximum at the center of interval Δω ex and weakens as ω moves away from Δω ex . Specific features at ω < Δω ex are studied using measurements of Imε GHz ( P λ ) and Reε GHz (P λ ) under fiber-optic irradiation ( P λ = 0–370 mW and λ = 0.97 µm) of Si samples in a waveguide resonator ( f = ω/2π = 4.7 GHz) and measurements of the dynamics of transmittance T ( P λ ) in free space ( f = 8–36 GHz). It is shown that quantities Reε GHz and Imε GHz increase with increasing P λ while the transmittance decreases and approaches saturation at P λ > 200 mW. For the same power P λ , the transmittance increases with decreasing frequency.