Ultrafast Long-Distance Electron-Hole Plasma Expansion in GaAs Mediated by Stimulated Emission and Reabsorption of Photons

Tinkara Troha, Filip Klimovič, Tomáš Ostatnický, Filip Kadlec, Petr Kužel, and Hynek Němec

Phys. Rev. Lett. 130, 226301 – Published 31 May 2023

Abstract

Electron-hole plasma expansion with velocities exceeding $c / 50$ and lasting over 10 ps at 300 K was evidenced by time-resolved terahertz spectroscopy. This regime, in which the carriers are driven over $> 30 μ m$ is governed by stimulated emission due to low-energy electron-hole pair recombination and reabsorption of the emitted photons outside the plasma volume. At low temperatures a speed of $c / 10$ was observed in the regime where the excitation pulse spectrally overlaps with emitted photons, leading to strong coherent light-matter interaction and optical soliton propagation effects.

Received 23 June 2022
Revised 13 March 2023
Accepted 3 May 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.226301

Physics Subject Headings (PhySH)

Carrier dynamics

Semiconductors

Terahertz spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Tinkara Troha¹, Filip Klimovič ², Tomáš Ostatnický ², Filip Kadlec ¹, Petr Kužel¹, and Hynek Němec ^1,*

¹Institute of Physics ASCR, Na Slovance 2, 182 00 Prague 8, Czech Republic
²Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech Republic

^*Corresponding author. nemec@fzu.cz

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 130, Iss. 22 — 2 June 2023

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Increase in the plasma extent during the plasma expansion at room temperature. Symbols: measurements (using ODIN). Dashed lines: calculations (same parameters as in Fig. 3). Dotted line: slope corresponding to expansion velocity $c / 50$ . Zero time and plasma expansion distance are chosen such that the dynamics right after the full absorption of the excitation pulse is shown (see Secs. S1 and S2 of [13] for more details). (b) Comparison of the initial EHP extent $l_{0}$ and EHP expansion $Δ l (5 ps) = l (5 ps) - l_{0}$ , which can serve as a measure of the initial EHP expansion rate. (c) Optical spectrum (normalized by the excitation fluence) measured behind a $10 μ m$ thick GaAs (Spitfire ACE) and (d) corresponding integrated areas of the broad peak around 800 nm and of that close to 900 nm in (c).
Reuse & Permissions
Figure 2
(a) Illustration of processes occurring in the band structure of GaAs; see also Sec. S5 in [13]. (b)–(d) Schematics of the evolution of the carrier distribution in the real space: (b) immediately after photoexcitation, (c) after carrier cooling, and (d) during the plasma expansion regime.
Reuse & Permissions
Figure 3
Calculated dynamics of (a) the populations $n_{1}$ and (b) $n_{2}$ , and (c) of the optical power density $I_{2}$ . The magenta dash-dot line indicates the propagation of the peak of the excitation pulse $I_{1}$ (the deviations from the straight light line are caused by the pulse reshaping due to the nonlinear interaction with the reservoir). The dashed curve in (b) and (c) divides the region into areas below and above the population inversion threshold in the active level. The red solid curve shows the position where the terahertz pulse appears to be reflected (result of numerical calculations of terahertz beam propagation in the displayed gradient environment with carrier density $n_{1} + n_{2}$ ; see Sec. S3 in [13]). Parameters: incident excitation fluence $= 1.9 \times 10^{16} photons / {cm}^{2}$ , $N_{2} = 1.34 \times 10^{18} {cm}^{- 3}$ , $τ = 2 ps$ (estimate based on [34, 35, 36]), $N_{1} = 5 \times 10^{18} {cm}^{- 3}$ [10], $α = 1.3 {μ m}^{- 1}$ [37], $v = c / 4.2$ [37], $β = 220 cm / GW$ [10], $A = 1 {ns}^{- 1}$ [38], excitation pulse $length = 100 fs$ . The material parameters correspond to room temperature properties of GaAs. See Sec. S2 of [13] for the meaning of “time after excitation”.
Reuse & Permissions
Figure 4
Temperature dependence of (a) increase in plasma extent during its expansion and (b) velocity of plasma expansion at the excitation fluence $1.7 \times 10^{16} photons / {cm}^{2}$ . The lines in (b) are just smoothed data to guide the eye. Inset: amplitude of the spectrum of the detected THz pulse before and after photoexcitation of the front side, measured at $T = 20 K$ . The observed blue shift corresponds to the Doppler factor $\sqrt{(c / η_{THz} + u) / (c / η_{THz} - u)} \approx 1.46$ and it therefore independently confirms that the velocity of the plasma expansion $u$ is $\approx c / 10$ . Experiments with Spitfire ACE.
Reuse & Permissions

Physical Review Letters