Impact Ionization Induced by Terahertz Radiation in HgTe Quantum Wells of Critical Thickness

• Published in: Journal of infrared, millimeter and terahertz waves millimeter and terahertz waves, 2020-10, Vol.41 (10), p.1155-1169
• Main Authors: Hubmann, S., Budkin, G.V., Urban, M., Bel’kov, V.V., Dmitriev, A.P., Ziegler, J., Kozlov, D.A., Mikhailov, N.N., Dvoretsky, S.A., Kvon, Z.D., Weiss, D., Ganichev, S.D.
• Format: Article
• Language: English
• Subjects: Angular momentum; Classical Electrodynamics; Current carriers; Electric fields; Electrical Engineering; Electronics and Microelectronics; Energy gap; Engineering; Holes (electron deficiencies); Instrumentation; Ionization; Multiplication; Quantum wells; Radiation; Radiation effects; Relaxation time; Terahertz frequencies; Thickness
• ISSN: 1866-6892; 1866-6906
• DOI: 10.1007/s10762-020-00690-6

We report on the observation of terahertz (THz) radiation induced band-to-band impact ionization in HgTe quantum well (QW) structures of critical thickness, which are characterized by a nearly linear energy dispersion. The THz electric field drives the carriers initializing electron-hole pair generation. The carrier multiplication is observed for photon energies less than the energy gap under the condition that the product of the radiation angular frequency ω and momentum relaxation time τ l larger than unity. In this case, the charge carriers acquire high energies solely because of collisions in the presence of a high-frequency electric field. The developed microscopic theory shows that the probability of the light-induced impact ionization is proportional to exp ( − E 0 2 / E 2 ) , with the radiation electric field amplitude E and the characteristic field parameter E 0 . As observed in experiment, it exhibits a strong frequency dependence for ω τ ≫ 1 characterized by the characteristic field E 0 linearly increasing with the radiation frequency ω .