Probing Metastable Space-Charge Potentials in a Wide Band Gap Semiconductor

Artur Lozovoi, Harishankar Jayakumar, Damon Daw, Ayesha Lakra, and Carlos A. Meriles

Phys. Rev. Lett. 125, 256602 – Published 18 December 2020

Abstract

While the study of space-charge potentials has a long history, present models are largely based on the notion of steady state equilibrium, ill-suited to describe wide band gap semiconductors with moderate to low concentrations of defects. Here we build on color centers in diamond both to locally inject carriers into the crystal and probe their evolution as they propagate in the presence of external and internal potentials. We witness the formation of metastable charge patterns whose shape—and concomitant field—can be engineered through the timing of carrier injection and applied voltages. With the help of previously crafted charge patterns, we unveil a rich interplay between local and extended sources of space-charge field, which we then exploit to show space-charge-induced carrier guiding.

Received 21 May 2020
Revised 18 September 2020
Accepted 3 November 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.256602

Physics Subject Headings (PhySH)

Carrier dynamics Carrier generation & recombination Charge Electrical conductivity Electrical properties

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Artur Lozovoi ^1,*, Harishankar Jayakumar^1,*, Damon Daw ^1,2, Ayesha Lakra ¹, and Carlos A. Meriles ^1,2,†

¹Department of Physics, CUNY-City College of New York, New York, New York 10031, USA
²CUNY-Graduate Center, New York, New York 10016, USA

^*These authors contributed equally to this work.
^†Corresponding author. cmeriles@ccny.cuny.edu

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Vol. 125, Iss. 25 — 18 December 2020

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Images

Figure 1
Visualizing charge dynamics under constant potentials. (a) Schematics of the experimental setup. We accelerate photogenerated carriers using a pair of planar electrodes patterned on the diamond surface. (b) Calculated electric field within diamond assuming $V = 560 V$ . (c) Experimental protocol; zigzags indicate laser scans and solid squares correspond to laser parks. (d) Differential ${N V}^{-}$ fluorescence $δ F$ as a function of position after a green laser park at the image midpoint for different applied voltages; the laser parking time is $t_{P} = 1 \min$ and the arrow denotes the direction of the externally applied electric field $E$ . The growing dark tail corresponds to the acceleration of holes toward the right, from high to low potentials.
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Figure 2
Modeling space-charge potentials. (a) Numerical simulation of NV charge patterns for variable field $E_{ext}$ assuming a diamond with NV (nitrogen) concentration of 2.5 ppb (0.25 ppm). In all calculations, the field is assumed constant throughout the sample. Arrows indicate the point of illumination assuming a beam diameter of $1 μ m$ ; the total green laser park time is 20 ms. Space-charge (SC) effects are included in the right lower plot, where the induced field is seen to reach $0.075 V / μ m$ . (b) The application of external bias leads to charge separation and thus space-charge formation (i), subsequently altering the path of incoming carriers (ii).
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Figure 3
${\tilde{t}}_{E} = n (t_{P 1} + t_{P 2})$ Charge dynamics in the presence of pulsed electric fields. (a) Experimental protocol (top left); the total parking time amounts to . [(i)–(v)] Differential ${N V}^{-}$ fluorescence maps for different applied voltages; in these experiments, $t_{P 1} = 1 ms$ , $t_{P 2} = 1 ms$ , ${\tilde{t}}_{P} = 1 \min$ , and the arrow denotes the direction of the externally applied electric field. (b) (Left) Same as above but for $t_{P 2} = 10 μ s$ (right) or $t_{P 2} = 0 μ s$ (left) at 420 V. The same color bar applies to both (a) and (b).
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Figure 4
${\tilde{t}}_{P} = 10 s$ Probing local and nonlocal space charge. (a) Experimental protocol. $F_{2}$ denotes the final fluorescence image and $F_{1}$ is the reference image after the first orange scan (optional, shown in a faint trace). (b) Fluorescence image $δ F^{'} = F_{2} - F_{1}$ upon use of the protocol in (a) for $t_{P 1} = t_{P 2} = 1 ms$ , $n = 5000$ , and . (c) Absolute ${N V}^{-}$ fluorescence image $F$ upon consecutive, uninterrupted green laser parks at positions (i) and (ii) (arrows). The voltage is $V = 420 V$ during park (i) and $V = 0 V$ during park (ii); all other conditions as in Fig. 1.
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